Vibration-Torsion-Rotation Study of the ν5 State of CH3CF3

An investigation of the torsion-rotation-vibration energies in the ν₅ vibrational state in CH₃CF₃ has been carried out using infrared and mm-wave spectroscopy. The lowest frequency parallel fundamental band ν₅ near 600 cm⁻¹ has been measured at a resolution of 0.00125 cm⁻¹ with Fourier transform spectroscopy for the two lowest torsional states v₆=0 and 1. The cold band (v₅=1, v₆=0)←(v₅=0, v₆=0) showed no torsional splittings and looked much like a parallel band in a C_3v molecule. The hot band (v₅=1, v₆=1)←(v₅=0, v₆=1) consisted of three distinct subbands, one for each torsional sublevel σ=0, +1, and −1. For the state (v₅=1, v₆=1), the torsional splitting was increased from ∼0.001 cm⁻¹ to ∼0.022 cm⁻¹ by torsion-mediated Fermi-type interaction primarily with the dark state (v₅=0, v₆=5). The effects of this coupling on the spectrum are striking in spite of the fact that the two interacting states are ∼100 cm⁻¹ apart and differ by four units in v₆. The large amplitude character of the state (v₅=0, v₆=5) is seen to be largely responsible for the unusual (k, σ) dependence of the energies in the state (v₅=1, v₆=1). The pure rotational spectrum in the state (v₅=1, v₆=0) has been measured between ∼50 and 370 GHz with Doppler-limited resolution; no σ-splitting was detected. The 3590 infrared and mm-wave frequencies measured here have been analyzed together with the 1494 measurements reported earlier by Wang et al. in an analysis of the vibrational ground state (2001, J. Mol. Spectrosc.205, 146-163). A good fit was obtained here by varying 36 parameters in a Hamiltonian which takes into account the interaction between the torsional stacks of levels for v₅=0 and 1, as well as the (A₁−A₂) splittings measured earlier for v₅=0. The explicit treatment of the interstack interactions is shown to lead to significant changes in the parameters (V_0,3, V_0,6) that characterize the torsional potential for v₅=0. These changes have been explained quantitatively by examining the contact transformation that is implicitly applied when the interstack coupling is neglected.     

CO2 and N2O laser Stark spectroscopy of the ν1 band of the ClO2 radical

The ν₁ fundamental band of the ClO₂ radical has been studied by means of the 10.6-μm CO₂ and N₂O laser Stark spectroscopy. More than 250 and 150 Stark resonances were assigned for the ³⁵ClO₂ and ³⁷ClO₂ species, respectively, and were analyzed together with the recent microwave and laser-microwave double resonance results to give molecular constants including spin-rotation interaction constants. The ν₁ band origins and electric dipole moments both in the ground and ν₁ states were determined accurately

     

3.

Analysis of ν₂, ν₄ Infrared Hot Bands of SO₃: Resolution of the Puzzle of the ν₁ CARS Spectrum     

Jeffrey BarberEngelene t.H. Chrysostom  Tony MasielloJoseph W. Nibler  Arthur MakiAlfons Weber  Thomas A. BlakeRobert L. Sams 《Journal of Molecular Spectroscopy》2002,216(1):105-112

Further analysis of the high-resolution (0.0015 cm⁻¹) infrared spectrum of ³²S¹⁶O₃ has led to the assignment of more than 3100 hot band transitions from the ν₂ and ν₄ levels to the states 2ν₂ (l=0), ν₂+ν₄ (l=±1), and 2ν₄ (l=0,±2). These levels are strongly coupled via Fermi resonance and indirect Coriolis interactions to the ν₁ levels, which are IR-inaccessible from the ground state. The unraveling of these interactions has allowed the solution of the unusual and complicated structure of the ν₁ CARS spectrum. This has been accomplished by locating over 400 hot-band transitions to levels that contain at least 10% ν₁ character. The complex CARS spectrum results from a large number of avoided energy-level crossings between these states. Accurate rovibrational constants are deduced for all the mixed states for the first time, leading to deperturbed values of 1064.924(11), 0.000 840 93(64), and 0.000 418 19(58) cm⁻¹ for ν₁, α₁^B, and α₁^C, respectively. The uncertainties in the last digits are shown in parentheses and represent two standard deviations. In addition, new values for some of the anharmonicity constants have been obtained. Highly accurate values for the equilibrium rotational constants B_e and C_e are deduced, yielding independent, nearly identical values for the SO r_e bond length of 141.734 03(13) and 141.732 54(18) pm, respectively.     

4.

Analysis of the hot bands in the 2ν₉ band region of propyne-d₃     

Geetha Rajappan 《Journal of Molecular Spectroscopy》2004,224(2):107-113

The rovibrational spectrum of 2ν₉ band of CD₃CCH is overlapped by two prominent hot bands identified as (2ν₉⁰+ν₁₀^±1)(E)←ν₁₀^±1(E) and 3ν₉^±1(E)←ν₉^±1(E), where ν₁₀ and ν₉ are the degenerate CCC and CCH bending fundamental vibrations, respectively. Assignment of lines to the transitions of these hot bands were carried out with the help of the high-resolution spectra recorded at ∼195 K and at room temperature. Molecular parameters for these hot bands have been obtained from the rotational analysis of the partially resolved K-structure lines. Only Q-head of the third hot band , originating from the lower 2ν₁₀ state could be identified.     

5.

High resolution study of the 3ν₁ band of SO₂     

O.N. Ulenikov  E.S. Bekhtereva  S. Alanko 《Journal of Molecular Spectroscopy》2009,255(2):111-121

The second overtone band 3ν₁ of sulfur dioxide has been studied for the first time with high resolution rotation-vibration spectroscopy. About 3000 transitions involving about 900 upper state energy levels with have been assigned to the 3ν₁ band. In the analysis, an effective Hamiltonian taking into account accidental interactions between the vibrational states (3 0 0), (2 2 0), and (0 4 1) was used. The Watson operator in A-reduction and I^r representation was used in the diagonal blocks of the Hamiltonian. As the result of analysis a set of parameters reproducing the initial experimental data with the rms = 0.00028 cm⁻¹ was obtained.     

6.

Stretch-Bender Calculations of the Rovibronic Energies in the Excited, ÃA₁, Electronic State of NH₂ and of the Near-Resonant High-Lying Levels of the X?B₁ State     

Geoffrey DuxburyAlexander Alijah 《Journal of Molecular Spectroscopy》2002,211(1):31-57

The extended stretch-bender Hamiltonian, incorporating spin-orbit coupling and overall rotation, has been used to calculate the spin-vibronic structure of the rovibronic energies in the region where the vibronic states of the excited òA₁ electronic state of NH₂ interact with near-resonant high-lying levels of the X?²B₁ state of NH₂. A detailed comparison has been made with the experimental measurements which were made of these rovibronic states, the majority of which are due to Ramsay, Vervloet, and their collaborators. We have shown that, as in our study of the vibronic levels of the X?²B₁ state below the barrier to linearity, in order to fit the variation of the effective vibronic spin-orbit coupling constant over the whole of this energy regime, the effective linear molecule spin-orbit coupling constant, A_SO must be increased from the earlier value of 50 cm⁻¹ of Ch. Jungen, K.-E. J. Hallin, and A. Merer (Mol. Phys.40, 65-94 (1980)) to 61.6 cm⁻¹. The impact of Fermi resonance, in both the òA₁ and X?²B₁ states, on the observed rovibronic structure has been assessed. The pattern of calculated spin-rovibronic levels, including the effects of spin uncoupling, is in good agreement with that measured experimentally.     

7.

Infrared diode laser spectroscopy of the ν₃ fundamental band of the PO₂ free radical     

Michael A. Lawson  Kristian J. Hoffman  Paul B. Davies 《Journal of Molecular Spectroscopy》2011,269(1):61-76

The asymmetric stretching fundamental of the PO₂ free radical in its ground electronic state has been measured between 1280 and 1360 cm⁻¹ using diode laser absorption spectroscopy. This new data set has been combined in a fit with an earlier, smaller infrared data set and with pure rotational transitions measured by microwave and laser magnetic resonance spectroscopies to provide a new set of parameters for the ground and ν₃ = 1 states of A₁ PO₂. These parameters can be used to calculate line positions in this band for transitions up to N = 50.     

8.

High-Resolution FTIR Spectra of CD₂Cl₂: Analysis of the ν₃/ν₇/ν₉ Triad     

Marcel Snels  Giuseppe D'AmicoEl Bachir Mkadmi 《Journal of Molecular Spectroscopy》2002,216(2):191-196

The infrared spectra of isotopically pure CD₂³⁵Cl₂ have been recorded at a resolution of 0.0026 cm⁻¹ (FWHM) in the range 600-1160 cm⁻¹ with a Bruker IFS 120 HR Fourier transform interferometer. The absorption between 670 and 750 cm⁻¹ is due to three fundamentals, ν₃ (weak), ν₇ (very weak), and ν₉ (strong). A satisfactory analysis of the observed spectra has been obtained by including a c-Coriolis coupling between ν₃ and ν₉ and a b-Coriolis term between ν₇ and ν₉. Although no transitions could be observed for the very weak ν₇ band, its band origin could be estimated from the Coriolis interaction with ν₉. From the analysis of about 4200 assigned transitions of the ν₃ and ν₉ bands, excited state constants have been determined up to sextic terms. The Coriolis parameters obtained are compared to those calculated from a harmonic force field.     

9.

CO₂ laser-microwave double resonance and stark lamb-dip spectroscopy of the ν₅ band of CDF₃     

Kensuke Harada  Makoto Hatanaka  Akira Inayoshi  Keiichi Tanaka  Takehiko Tanaka 《Journal of Molecular Spectroscopy》1984,108(2):249-263

The LMDR (laser-microwave double resonance) spectroscopy with an intense electric field was applied to the ν₅ (CF₃ degenerate stretch) fundamental band of CDF₃. The dipole moments and polarizability anisotropies in the ground and ν₅ vibrational states were determined as follows.

		35ClO2		37ClO2
$\text{ν}{}_0$		945.592 357(60)		939.602 909(66)		cm?1
μ′		1.788 39(13)		1.788 46(15)		D
μ″		1.791 95(10)		1.792 10(13)		D
δμ		?0.003 56(18)		?0.003 64(26)		D

     

10.

The 10.4 μm CO₂ laser Stark spectra of the ν₄ and the ν₉ bands of 1,1 difluoroethylene     

G Duxbury  H Herman 《Journal of Molecular Spectroscopy》1978,73(3):444-461

The ν₄ and the ν₉ bands of CF₂CH₂ have been studied using coincidences with the 10.4 μm band of the CO₂ laser and the 10.9 μm band of the N₂O laser. These resonances have been analyzed, together with recent microwave results, to give the following vibration-rotation parameters and dipole moments in the ν₄ and ν₉ states

	Ground	$\text{ν}{}_5$
μ (D)	1.653 511 (29)	1.658 514 (23)
α (Å3)	?0.77 (32)	?0.58 (48)

     

11.

Stimulated Emission Pumping Spectroscopy of SiH₂: First Observation of the Spin-Orbit Interaction between the X?A₁ and the ãB₁ States     

Haruki IshikawaYasuhiko Muramoto  Naohiko Mikami 《Journal of Molecular Spectroscopy》2002,216(1):90-97

Stimulated emission pumping spectra of the ùB₁-X?¹A₁ transition of the SiH₂ radical were observed in order to obtain information about the ã³B₁ state through the spin-orbit interaction. The vibrational level structure of the X? state, which is the basis for the present observation of the triplet state, was well described with a polyad structure, in which both the 1ν₁ : 2ν₂ Fermi and the 2ν₁ : 2ν₃ Darling-Dennison anharmonic resonances were considered. In the P=10 polyad, four sets of spin-orbit perturbations were observed for the first time. The triplet state observed at about 9640 cm⁻¹ from the (000) level of the X? state was tentatively assigned as the ã³B₁ (030) level. An analysis of the spin-orbit interaction showed that the interaction energies of the spin-orbit coupling are 0.73-3.13 cm⁻¹. This value is rather smaller than that expected based on the comparison with CH₂. This is considered to be due to poor overlap between the vibrational wave functions in the ã and the X? state.     

12.

Forbidden lines of the ν₃ band of ¹³CH₄: Ground-state constants     

Lary W. Pinkley  K. Narahari Rao  M. Dang-Nhu  G. Tarrago  G. Poussigue 《Journal of Molecular Spectroscopy》1976,63(3):402-444

The ν₃ fundamental vibration-rotation band of carbon-13 enriched methane (¹³CH₄) was recorded using a high-resolution vacuum infrared grating spectrograph. Forbidden transitions of this band are reported for the first time. Of the nearly 900 transitions identified, 560 are forbidden transitions and 347 of the forbidden transitions have 11 ≤ J ≤ 18. Pairs of forbidden and allowed transitions having the same upper-state energy levels were used to calculate 550 independent differences between ground-state term values. From these data, a least-squares analysis was used to calculate the following values for ground-state structure constants and their standard deviations (in cm^?1):

$\text{β}{}^{\mathrm{O}}\text{hc}\text{= 5.240820 ± 0.000056}$

,

$\text{λ}{}^{\mathrm{O}}\text{hc}\text{=?(1.0856 ± 0.0015) × 10}{}^{\mathrm{?4}}$

,

$\text{?}{}^{\mathrm{O}}\text{hc}\text{= ?(1.4174 ± 0.0034) × 10}{}^{\mathrm{?4}}$

,

$\text{η}\text{hc}\text{= ?(1.73 ± 0.37) × 10}{}^{\mathrm{?11}}$

. The 550 values for the ground-state combination differences retained for analysis can be reproduced with an overall standard deviation of 0.0155 using the stated values for the structure constants. The note added in proof refines the above constants by including the newly observed microwave data.     

13.

High resolution analysis of the ν₇ and ν₉ bands of DCOOH     

O.I. Baskakov  V.-M. Horneman 《Journal of Molecular Spectroscopy》2003,219(2):191-199

The 7¹ and 9¹ vibrational states of deuterated species of formic acid molecule DCOOH have been recorded by a FTIR spectrometer in the region 450- at a resolution of and a millimeter wave spectrometer. In the analysis microwave transitions from literature were used in addition to 14 835 assigned IR and 114 millimeter wave lines in the 7¹ and 9¹ vibrational states. The analysis resulted in band origins, rotational, centrifugal distortion, and eight interaction parameters of the Coriolis coupled 7¹ and 9¹ vibrational states. RMS deviation of the fit was for the IR data and the maximum values of J and K_a quantum numbers in the fit were 64, 28 and 64, 30 for 7¹ and 9¹ states, respectively.     

14.

Observation of simultaneous ν₁(SF₆) + ν₃(NF₃) and ν₂(SF₆) + ν₃(NF₃) transitions enhanced by the resonance dipole-dipole interaction with the ν₁ + ν₃ and ν₂ + ν₃ states of the SF₆ molecule     

V. N. Bocharov  A. P. Burtsev  E. V. Dubrovskaya  T. D. Kolomiitsova  D. N. Shchepkin 《Optics and Spectroscopy》2010,108(4):533-543

IR spectra of the solution of SF₆ molecules in liquid NF₃ at 84 K have been recorded. In a solvent transmission window of 1500–1750 cm⁻¹, two wide absorption bands with pronounced peaks in the high-frequency part are observed. The profile of these bands is explained by the influence of the resonance dipole-dipole (RDD) interaction of the states of the simultaneous transition ν₁(SF₆) + ν₃(NF₃) and ν₂(SF₆) + ν₃(NF₃) with the states (ν₁ + ν₃) and (ν₂ + ν₃) of the SF₆ molecules, respectively. The use of three isotopic modifications ³²SF₆, ³³SF₆, and ³⁴SF₆ has allowed us to vary the resonance detuning and thus to change the strength of the RDD interaction. With the liquid near the melting point being represented as a close-packed cubic crystal, the profile was calculated and its spectral characteristics were determined. The frequencies of the main peaks coincide with the experimental values accurate to the error.     

15.

Infrared spectra of two isomers of OCS-C₂H₂ and OCS-C₂D₂ in the region of OCS ν₁ fundamental     

J. Norooz Oliaee  M. Dehghany  A.R.W. McKellar 《Journal of Molecular Spectroscopy》2009,257(2):133-10422

Infrared spectra of OCS-C₂H₂ and OCS-C₂D₂ complexes in the region of the C-O stretching fundamental of OCS (∼2060 cm⁻¹) are studied in a pulsed supersonic slit-jet expansion using a tunable diode laser. For each complex, two bands are observed and assigned to distinct near-parallel and the T-shaped isomers. Ground state parameters were previously determined from microwave studies, so analysis of the infrared spectra gives information on the vibrational shifts upon complex formation as well as rotational and centrifugal distortion parameters for the excited states. All four bands show a red shift with respect to the monomer band origin, with the T-shaped isomer having a much larger shift than the near-parallel isomer. Disappearance of the T-shaped isomer when argon is used as a carrier gas supports the notion that the near-parallel isomer is the lowest energy form of the complex.     

16.

CO₂ laser Stark spectroscopy of the Coriolis-coupled ν₂ and ν₅ bands of CD₃Br     

Kensuke Harada  Keiichi Tanaka  Takehiko Tanaka 《Journal of Molecular Spectroscopy》1983,98(2):349-374

The ν₂ (CD₃ symmetrical deformation) and ν₅ (CD₃ degenerate deformation) fundamental bands of CD₃Br were studied by 9.4- and 10.4-μm CO₂ laser Stark spectroscopy. Stark resonances originating from 28 and 53 rovibrational transitions of the ν₂ and ν₅ bands, respectively, were assigned for each of the isotopic species, CD₃⁷⁹Br and CD₃⁸¹Br. These two bands were simultaneously analyzed with explicit inclusion of the ν₂-ν₅ Coriolis interaction, yielding precise molecular constants in the ν₂ and ν₅ excited states as well as the Coriolis coupling constant. The molecular constants obtained are consistent between the two isotopic species and are in good agreement with the results of high-resolution infrared studies. The band origins and dipole moments are

	$\text{ν}{}_4$ CF2CH2	$\text{ν}{}_9$ CF2CH2
$\text{ν}{}_0$	925.7692 (2)	953.8057 (2)	cm?1
$\text{A}$	10 971.99 (2)	11 026.918 (6)	MHz
$\text{B}$	10 414.98 (2)	10 436.381 (6)	MHz
$\text{C}$	5328.48 (2)	5346.100 (6)	MHz
μ	1.382 (1)	1.382 (1)	D
$\text{μ - μ}{}_0$	0.014 (2)	0.004 (1)	D

     

17.

New analysis of the ν₅+ν₉−ν₉ hot band of HNO₃     

J.-M Flaud  J Orphal  P.-M Flaud  C Piccolo 《Journal of Quantitative Spectroscopy & Radiative Transfer》2003,77(4):355-364

Nitric acid which is an important NO_x atmospheric reservoir molecule exhibits a strong absorption in the spectral region. Since this region, which corresponds to an atmospheric window, is one of the most commonly used for the retrieval of HNO₃ in the atmosphere it is essential to have the best possible corresponding spectral parameters. Updates of these spectral line parameters were recently performed in the last versions of the atmospheric databases. They concern the line positions and intensities not only of the two interfering cold bands ν₅ and 2ν₉ but also of the ν₅+ν₉−ν₉ hot band. This hot band exhibits indeed a sharp and strong Q branch at which is clearly observable in atmospheric spectra and is used for the retrievals. However, in spite of these recent updates, it proved that the spectral parameters of the hot band are not accurate enough to reproduce accurately the observed atmospheric HNO₃ absorption in ATMOS spectra. The present paper is dedicated to a more accurate analysis of this hot band using new laboratory high-resolution (0.002-) Fourier transform spectra. As a consequence, new and more precise line positions and line intensities (about 35% weaker than in HITRAN2K) were derived leading to a significant improvement in the simulation of atmospheric spectra.     

18.

High-resolution study of the ν₁/ν₅ and 2ν₁/ν₁+ν₅ P-H stretching bands of PH₂D     

O.N. Ulenikov  E.S. Bekhtereva  O.L. Petrunina  H. Bürger 《Journal of Molecular Spectroscopy》2003,219(1):13-29

The P-H stretching bands ν₁/ν₅ and 2ν₁/ν₁+ν₅ were recorded using a Bruker 120 HR interferometer with a resolution of 0.0042 and 0.0088 cm⁻¹, respectively, and analyzed. From the fits 33 and 50, respectively, vibrational, rotational, centrifugal distortion, and resonance interaction parameters were obtained. These reproduce 668 and 497 rovibrational energies of the pairs of states ν₁/ν₅ and 2ν₁/ν₁+ν₅ with experimental accuracies, rms=0.00016 and , respectively. “Local mode” behavior of the PH₂ fragment is established and discussed in detail.     

19.

H₂-broadening coefficients in the ν₂ and ν₄ bands of PH₃     

Jean-Pierre Bouanich  Jamel Salem  Jacques Walrand 《Journal of Quantitative Spectroscopy & Radiative Transfer》2004,84(2):195-205

H₂-broadening coefficients are measured for 41 transitions of PH₃ in the QR branch of the ν₂ band and the PP, RP, and PQ branches of the ν₄ band, using a tunable diode-laser spectrometer. The recorded lines with J values ranging from 2 to 16 and K from 0 to 11 are located between 995 and . The collisional widths are determined by fitting each spectral line with a Voigt profile, a Rautian profile, and a speed-dependent Rautian profile. The latter model provides larger broadening coefficients than the Voigt model. These coefficients γ₀(J,K) are found to decrease slightly on the whole as J increases and they decrease significantly for K values approaching or equal to J(J?4). The H₂-broadenings are also calculated on the basis of a semiclassical model of interacting linear molecules, using an atom-atom Lennard-Jones potential in addition to the weak electrostatic contributions. The theoretical results are in satisfactory agreement with the experimental data and reproduce the J and K dependencies of the broadenings, but the decrease observed for the QR(J,K) transitions with K=J is notably overestimated.     

20.

Bifurcations of the normal modes of the Ne?Br₂ complex     

Fernando Blesa  J. Pablo Salas 《Physics letters. A》2009,374(2):191-201

We study the classical dynamics of the rare gas-dihalogen Ne?Br₂ complex in its ground electronic state. By considering the dihalogen bond frozen at its equilibrium distance, the system has two degrees of freedom and its potential energy surface presents linear and T-shape isomers. We find the nonlinear normal modes of both isomers that determine the phase space structure of the system. By means of surfaces of section and applying the numerical continuation of families of periodic orbits, we detect and identify the different bifurcations suffered by the normal modes as a function of the system energy. Finally, using the Orthogonal Fast Lyapunov Indicator (OFLI), we study the evolution of the fraction of the phase space volume occupied by regular motions.     

		CD379Br		CD381Br
$\text{ν}{}_2$		991.396 82 (18)		991.388 46 (17)		cm?1
$\text{ν}{}_5$		1055.469 00 (12)		1055.466 32 (12)		cm?1
$\text{μ}{}_0$		1.830 42 (52)		1.829 84 (47)		D
$\text{μ}{}_2$		1.829 93 (48)		1.829 57 (46)		D
$\text{μ}{}_5$		1.832 23 (60)		1.831 19 (56)		D

Analysis of ν2, ν4 Infrared Hot Bands of SO3: Resolution of the Puzzle of the ν1 CARS Spectrum

Further analysis of the high-resolution (0.0015 cm⁻¹) infrared spectrum of ³²S¹⁶O₃ has led to the assignment of more than 3100 hot band transitions from the ν₂ and ν₄ levels to the states 2ν₂ (l=0), ν₂+ν₄ (l=±1), and 2ν₄ (l=0,±2). These levels are strongly coupled via Fermi resonance and indirect Coriolis interactions to the ν₁ levels, which are IR-inaccessible from the ground state. The unraveling of these interactions has allowed the solution of the unusual and complicated structure of the ν₁ CARS spectrum. This has been accomplished by locating over 400 hot-band transitions to levels that contain at least 10% ν₁ character. The complex CARS spectrum results from a large number of avoided energy-level crossings between these states. Accurate rovibrational constants are deduced for all the mixed states for the first time, leading to deperturbed values of 1064.924(11), 0.000 840 93(64), and 0.000 418 19(58) cm⁻¹ for ν₁, α₁^B, and α₁^C, respectively. The uncertainties in the last digits are shown in parentheses and represent two standard deviations. In addition, new values for some of the anharmonicity constants have been obtained. Highly accurate values for the equilibrium rotational constants B_e and C_e are deduced, yielding independent, nearly identical values for the SO r_e bond length of 141.734 03(13) and 141.732 54(18) pm, respectively.     

Analysis of the hot bands in the 2ν9 band region of propyne-d3

The rovibrational spectrum of 2ν₉ band of CD₃CCH is overlapped by two prominent hot bands identified as (2ν₉⁰+ν₁₀^±1)(E)←ν₁₀^±1(E) and 3ν₉^±1(E)←ν₉^±1(E), where ν₁₀ and ν₉ are the degenerate CCC and CCH bending fundamental vibrations, respectively. Assignment of lines to the transitions of these hot bands were carried out with the help of the high-resolution spectra recorded at ∼195 K and at room temperature. Molecular parameters for these hot bands have been obtained from the rotational analysis of the partially resolved K-structure lines. Only Q-head of the third hot band , originating from the lower 2ν₁₀ state could be identified.     

High resolution study of the 3ν1 band of SO2

The second overtone band 3ν₁ of sulfur dioxide has been studied for the first time with high resolution rotation-vibration spectroscopy. About 3000 transitions involving about 900 upper state energy levels with have been assigned to the 3ν₁ band. In the analysis, an effective Hamiltonian taking into account accidental interactions between the vibrational states (3 0 0), (2 2 0), and (0 4 1) was used. The Watson operator in A-reduction and I^r representation was used in the diagonal blocks of the Hamiltonian. As the result of analysis a set of parameters reproducing the initial experimental data with the rms = 0.00028 cm⁻¹ was obtained.     

Stretch-Bender Calculations of the Rovibronic Energies in the Excited, ÃA1, Electronic State of NH2 and of the Near-Resonant High-Lying Levels of the X?B1 State

The extended stretch-bender Hamiltonian, incorporating spin-orbit coupling and overall rotation, has been used to calculate the spin-vibronic structure of the rovibronic energies in the region where the vibronic states of the excited òA₁ electronic state of NH₂ interact with near-resonant high-lying levels of the X?²B₁ state of NH₂. A detailed comparison has been made with the experimental measurements which were made of these rovibronic states, the majority of which are due to Ramsay, Vervloet, and their collaborators. We have shown that, as in our study of the vibronic levels of the X?²B₁ state below the barrier to linearity, in order to fit the variation of the effective vibronic spin-orbit coupling constant over the whole of this energy regime, the effective linear molecule spin-orbit coupling constant, A_SO must be increased from the earlier value of 50 cm⁻¹ of Ch. Jungen, K.-E. J. Hallin, and A. Merer (Mol. Phys.40, 65-94 (1980)) to 61.6 cm⁻¹. The impact of Fermi resonance, in both the òA₁ and X?²B₁ states, on the observed rovibronic structure has been assessed. The pattern of calculated spin-rovibronic levels, including the effects of spin uncoupling, is in good agreement with that measured experimentally.     

Infrared diode laser spectroscopy of the ν3 fundamental band of the PO2 free radical

The asymmetric stretching fundamental of the PO₂ free radical in its ground electronic state has been measured between 1280 and 1360 cm⁻¹ using diode laser absorption spectroscopy. This new data set has been combined in a fit with an earlier, smaller infrared data set and with pure rotational transitions measured by microwave and laser magnetic resonance spectroscopies to provide a new set of parameters for the ground and ν₃ = 1 states of A₁ PO₂. These parameters can be used to calculate line positions in this band for transitions up to N = 50.     

High-Resolution FTIR Spectra of CD2Cl2: Analysis of the ν3/ν7/ν9 Triad

The infrared spectra of isotopically pure CD₂³⁵Cl₂ have been recorded at a resolution of 0.0026 cm⁻¹ (FWHM) in the range 600-1160 cm⁻¹ with a Bruker IFS 120 HR Fourier transform interferometer. The absorption between 670 and 750 cm⁻¹ is due to three fundamentals, ν₃ (weak), ν₇ (very weak), and ν₉ (strong). A satisfactory analysis of the observed spectra has been obtained by including a c-Coriolis coupling between ν₃ and ν₉ and a b-Coriolis term between ν₇ and ν₉. Although no transitions could be observed for the very weak ν₇ band, its band origin could be estimated from the Coriolis interaction with ν₉. From the analysis of about 4200 assigned transitions of the ν₃ and ν₉ bands, excited state constants have been determined up to sextic terms. The Coriolis parameters obtained are compared to those calculated from a harmonic force field.     

CO2 laser-microwave double resonance and stark lamb-dip spectroscopy of the ν5 band of CDF3

The LMDR (laser-microwave double resonance) spectroscopy with an intense electric field was applied to the ν₅ (CF₃ degenerate stretch) fundamental band of CDF₃. The dipole moments and polarizability anisotropies in the ground and ν₅ vibrational states were determined as follows.

The 10.4 μm CO2 laser Stark spectra of the ν4 and the ν9 bands of 1,1 difluoroethylene

The ν₄ and the ν₉ bands of CF₂CH₂ have been studied using coincidences with the 10.4 μm band of the CO₂ laser and the 10.9 μm band of the N₂O laser. These resonances have been analyzed, together with recent microwave results, to give the following vibration-rotation parameters and dipole moments in the ν₄ and ν₉ states

Stimulated Emission Pumping Spectroscopy of SiH2: First Observation of the Spin-Orbit Interaction between the X?A1 and the ãB1 States

Stimulated emission pumping spectra of the ùB₁-X?¹A₁ transition of the SiH₂ radical were observed in order to obtain information about the ã³B₁ state through the spin-orbit interaction. The vibrational level structure of the X? state, which is the basis for the present observation of the triplet state, was well described with a polyad structure, in which both the 1ν₁ : 2ν₂ Fermi and the 2ν₁ : 2ν₃ Darling-Dennison anharmonic resonances were considered. In the P=10 polyad, four sets of spin-orbit perturbations were observed for the first time. The triplet state observed at about 9640 cm⁻¹ from the (000) level of the X? state was tentatively assigned as the ã³B₁ (030) level. An analysis of the spin-orbit interaction showed that the interaction energies of the spin-orbit coupling are 0.73-3.13 cm⁻¹. This value is rather smaller than that expected based on the comparison with CH₂. This is considered to be due to poor overlap between the vibrational wave functions in the ã and the X? state.     

Forbidden lines of the ν3 band of 13CH4: Ground-state constants

The ν₃ fundamental vibration-rotation band of carbon-13 enriched methane (¹³CH₄) was recorded using a high-resolution vacuum infrared grating spectrograph. Forbidden transitions of this band are reported for the first time. Of the nearly 900 transitions identified, 560 are forbidden transitions and 347 of the forbidden transitions have 11 ≤ J ≤ 18. Pairs of forbidden and allowed transitions having the same upper-state energy levels were used to calculate 550 independent differences between ground-state term values. From these data, a least-squares analysis was used to calculate the following values for ground-state structure constants and their standard deviations (in cm^?1):

$\text{β}{}^{\mathrm{O}}\text{hc}\text{= 5.240820 ± 0.000056}$

,

$\text{λ}{}^{\mathrm{O}}\text{hc}\text{=?(1.0856 ± 0.0015) × 10}{}^{\mathrm{?4}}$

,

$\text{?}{}^{\mathrm{O}}\text{hc}\text{= ?(1.4174 ± 0.0034) × 10}{}^{\mathrm{?4}}$

,

$\text{η}\text{hc}\text{= ?(1.73 ± 0.37) × 10}{}^{\mathrm{?11}}$

. The 550 values for the ground-state combination differences retained for analysis can be reproduced with an overall standard deviation of 0.0155 using the stated values for the structure constants. The note added in proof refines the above constants by including the newly observed microwave data.     

High resolution analysis of the ν7 and ν9 bands of DCOOH

The 7¹ and 9¹ vibrational states of deuterated species of formic acid molecule DCOOH have been recorded by a FTIR spectrometer in the region 450- at a resolution of and a millimeter wave spectrometer. In the analysis microwave transitions from literature were used in addition to 14 835 assigned IR and 114 millimeter wave lines in the 7¹ and 9¹ vibrational states. The analysis resulted in band origins, rotational, centrifugal distortion, and eight interaction parameters of the Coriolis coupled 7¹ and 9¹ vibrational states. RMS deviation of the fit was for the IR data and the maximum values of J and K_a quantum numbers in the fit were 64, 28 and 64, 30 for 7¹ and 9¹ states, respectively.     

Observation of simultaneous ν1(SF6) + ν3(NF3) and ν2(SF6) + ν3(NF3) transitions enhanced by the resonance dipole-dipole interaction with the ν1 + ν3 and ν2 + ν3 states of the SF6 molecule

IR spectra of the solution of SF₆ molecules in liquid NF₃ at 84 K have been recorded. In a solvent transmission window of 1500–1750 cm⁻¹, two wide absorption bands with pronounced peaks in the high-frequency part are observed. The profile of these bands is explained by the influence of the resonance dipole-dipole (RDD) interaction of the states of the simultaneous transition ν₁(SF₆) + ν₃(NF₃) and ν₂(SF₆) + ν₃(NF₃) with the states (ν₁ + ν₃) and (ν₂ + ν₃) of the SF₆ molecules, respectively. The use of three isotopic modifications ³²SF₆, ³³SF₆, and ³⁴SF₆ has allowed us to vary the resonance detuning and thus to change the strength of the RDD interaction. With the liquid near the melting point being represented as a close-packed cubic crystal, the profile was calculated and its spectral characteristics were determined. The frequencies of the main peaks coincide with the experimental values accurate to the error.     

Infrared spectra of two isomers of OCS-C2H2 and OCS-C2D2 in the region of OCS ν1 fundamental

Infrared spectra of OCS-C₂H₂ and OCS-C₂D₂ complexes in the region of the C-O stretching fundamental of OCS (∼2060 cm⁻¹) are studied in a pulsed supersonic slit-jet expansion using a tunable diode laser. For each complex, two bands are observed and assigned to distinct near-parallel and the T-shaped isomers. Ground state parameters were previously determined from microwave studies, so analysis of the infrared spectra gives information on the vibrational shifts upon complex formation as well as rotational and centrifugal distortion parameters for the excited states. All four bands show a red shift with respect to the monomer band origin, with the T-shaped isomer having a much larger shift than the near-parallel isomer. Disappearance of the T-shaped isomer when argon is used as a carrier gas supports the notion that the near-parallel isomer is the lowest energy form of the complex.     

CO2 laser Stark spectroscopy of the Coriolis-coupled ν2 and ν5 bands of CD3Br

The ν₂ (CD₃ symmetrical deformation) and ν₅ (CD₃ degenerate deformation) fundamental bands of CD₃Br were studied by 9.4- and 10.4-μm CO₂ laser Stark spectroscopy. Stark resonances originating from 28 and 53 rovibrational transitions of the ν₂ and ν₅ bands, respectively, were assigned for each of the isotopic species, CD₃⁷⁹Br and CD₃⁸¹Br. These two bands were simultaneously analyzed with explicit inclusion of the ν₂-ν₅ Coriolis interaction, yielding precise molecular constants in the ν₂ and ν₅ excited states as well as the Coriolis coupling constant. The molecular constants obtained are consistent between the two isotopic species and are in good agreement with the results of high-resolution infrared studies. The band origins and dipole moments are

New analysis of the ν5+ν9−ν9 hot band of HNO3

Nitric acid which is an important NO_x atmospheric reservoir molecule exhibits a strong absorption in the spectral region. Since this region, which corresponds to an atmospheric window, is one of the most commonly used for the retrieval of HNO₃ in the atmosphere it is essential to have the best possible corresponding spectral parameters. Updates of these spectral line parameters were recently performed in the last versions of the atmospheric databases. They concern the line positions and intensities not only of the two interfering cold bands ν₅ and 2ν₉ but also of the ν₅+ν₉−ν₉ hot band. This hot band exhibits indeed a sharp and strong Q branch at which is clearly observable in atmospheric spectra and is used for the retrievals. However, in spite of these recent updates, it proved that the spectral parameters of the hot band are not accurate enough to reproduce accurately the observed atmospheric HNO₃ absorption in ATMOS spectra. The present paper is dedicated to a more accurate analysis of this hot band using new laboratory high-resolution (0.002-) Fourier transform spectra. As a consequence, new and more precise line positions and line intensities (about 35% weaker than in HITRAN2K) were derived leading to a significant improvement in the simulation of atmospheric spectra.     

High-resolution study of the ν1/ν5 and 2ν1/ν1+ν5 P-H stretching bands of PH2D

The P-H stretching bands ν₁/ν₅ and 2ν₁/ν₁+ν₅ were recorded using a Bruker 120 HR interferometer with a resolution of 0.0042 and 0.0088 cm⁻¹, respectively, and analyzed. From the fits 33 and 50, respectively, vibrational, rotational, centrifugal distortion, and resonance interaction parameters were obtained. These reproduce 668 and 497 rovibrational energies of the pairs of states ν₁/ν₅ and 2ν₁/ν₁+ν₅ with experimental accuracies, rms=0.00016 and , respectively. “Local mode” behavior of the PH₂ fragment is established and discussed in detail.     

H2-broadening coefficients in the ν2 and ν4 bands of PH3

H₂-broadening coefficients are measured for 41 transitions of PH₃ in the QR branch of the ν₂ band and the PP, RP, and PQ branches of the ν₄ band, using a tunable diode-laser spectrometer. The recorded lines with J values ranging from 2 to 16 and K from 0 to 11 are located between 995 and . The collisional widths are determined by fitting each spectral line with a Voigt profile, a Rautian profile, and a speed-dependent Rautian profile. The latter model provides larger broadening coefficients than the Voigt model. These coefficients γ₀(J,K) are found to decrease slightly on the whole as J increases and they decrease significantly for K values approaching or equal to J(J?4). The H₂-broadenings are also calculated on the basis of a semiclassical model of interacting linear molecules, using an atom-atom Lennard-Jones potential in addition to the weak electrostatic contributions. The theoretical results are in satisfactory agreement with the experimental data and reproduce the J and K dependencies of the broadenings, but the decrease observed for the QR(J,K) transitions with K=J is notably overestimated.     

Bifurcations of the normal modes of the Ne?Br2 complex

We study the classical dynamics of the rare gas-dihalogen Ne?Br₂ complex in its ground electronic state. By considering the dihalogen bond frozen at its equilibrium distance, the system has two degrees of freedom and its potential energy surface presents linear and T-shape isomers. We find the nonlinear normal modes of both isomers that determine the phase space structure of the system. By means of surfaces of section and applying the numerical continuation of families of periodic orbits, we detect and identify the different bifurcations suffered by the normal modes as a function of the system energy. Finally, using the Orthogonal Fast Lyapunov Indicator (OFLI), we study the evolution of the fraction of the phase space volume occupied by regular motions.