A High-Resolution FT-IR Study of the Fundamental Bands ν6, ν10, and ν11 of trans-Glyoxal

The high-resolution Fourier transform infrared spectrum of trans-glyoxal in the gas phase has been recorded in the spectral regions 700-900 cm⁻¹, 1200-1400 cm⁻¹, and 1600-1800 cm⁻¹ with a resolution ranging from 0.0020 to 0.0025 cm⁻¹. The spectrum displays extensive rotational structures which are assigned to the three fundamental bands ν₆ (A_u, 801.5 cm⁻¹), ν₁₀ (B_u, 1732.1 cm⁻¹), and ν₁₁ (B_u, 1312.5 cm⁻¹). A total of ca. 5000 absorption lines have been assigned to these three bands. A simultaneous ground state combination difference analysis of all three bands yields improved ground state spectroscopic constants for trans-glyoxal. Furthermore, a number of spectroscopic constants for the ν₆ and ν₁₁ levels have been determined for the first time.     

High-Resolution Analysis of the ν6, ν17, and ν21 Bands of Dimethyl Ether

The ν₆, ν₁₇, and ν₂₁ fundamental bands of dimethyl ether have been assigned and rotationally analyzed. The spectra used were recorded at 0.005 cm⁻¹ spectral resolution with a Fourier-transform spectrometer coupled to a supersonic molecular beam leading to a rotational temperature of about 70 K. The ν₆ and ν₂₁ bands do not seem to be perturbed and the analysis of the rotational structure leads to band centers located at 933.906 6(9) and 1 103.951(1) cm⁻¹, respectively, and to accurate rotational and centrifugal distortion constants. For the ν₁₇ band at 2817.385(2) cm⁻¹, only the P and R branches could be assigned.     

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.     

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.     

On the Study of Resonance Interactions and Splittings in the PH3 Molecule: ν1, ν3, ν2+ν4, and 2ν4 Bands

The high-resolution (0.005 cm⁻¹) Fourier transform infrared spectrum of PH₃ is recorded and analyzed in the region of the fundamental stretching bands, ν₁ and ν₃. The ν₂+ν₄ and 2ν₄ bands are taken into account also. Experimental transitions are assigned to the ν₁, ν₃, ν₂+ν₄, and 2ν₄ bands with the maximum value of quantum number J equal to 15, 15, 13, and 15, respectively. a₁-a₂ splittings are observed and described up to the value of quantum number K equal to 10. The analysis of a₁/a₂ splittings is fulfilled with a Hamiltonian model which takes into account numerous resonance interactions among all the upper vibrational states.     

A High-Resolution Analysis of the ν3 Absorption Band of Trifluoromethane

A high-resolution (up to 0.0018 cm⁻¹ unapodized) room temperature mid-infrared (650 to 750 cm⁻¹, 13.3 to 15.4 μm) absorption measurement of the ν₃ vibrational band of trifluoromethane (fluoroform, CHF₃, HFC-23) vapor was made with a Fourier transform spectrometer. A rovibrational analysis of over 1400 infrared transitions of the ν₃ band has yielded rotational constants, including sextic centrifugal distortion constants. The results are compared with two previous analyses of microwave and infrared spectra. The line positions of the lower J parts of the ν₃+ν₆−ν₆ and 2ν₃−ν₃ hot bands have been identified and constants obtained for the 2ν₃ state. The central Q branch and a few unblended transitions of the ν₃ band of ¹³CF₃H have been identified and the band origin has been determined. The relative intensities of the ν₃ band together with the 2ν₃−ν₃ hot band and ν₃ band of ¹³CF₃H have been calculated using the constants derived from this work.     

The ν1, ν2, and ν3 Band Systems of 3-Isocyano-2-propynenitrile (NCCCNC): Comparison with the ν4 System of Dicyanoacetylene

The hot bands in the ν₁, ν₂, and ν₃ band systems of NC-CC-NC (3-isocyano-2-propynenitrile) have been investigated and transitions from nv₉-levels with n up to 4 have been identified. Two weak bands have also been observed in the gas phase infrared spectrum at 2157 and 2410 cm⁻¹, of which the latter is probably 2v₄. A preliminary investigation of some analogous hot bands in the v₄ band system of the related molecule NC-CC-CN (dicyanoacetylene) is also reported.     

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.     

The (ν1, ν4, ν2+ν3, ν3+ν5) Polyad of D3SiF around 1600 cm, Studied by High-Resolution FTIR Spectroscopy

The ν₁ (A₁, 1578.31 cm⁻¹)/ν₄(E, 1615.17 cm⁻¹) Si-D stretching dyad of D₃SiF has been studied by FTIR spectroscopy with a resolution of 2.4×10⁻³ cm⁻¹. Only weak interactions of Coriolis (ΔK=±1, Δ?=±1) and α resonance (ΔK=±2, Δ?=?1) type between ν₁ and ν₄, and of ? (2,−4) type within ν₄, were revealed. However, the v₁=1 and v₄=1 levels were found to be severely perturbed by the v₃=v₅=1 (E, 1590.37 cm⁻¹) and v₂=v₃=1 (A₁, 1604.25 cm⁻¹) states. These perturbations are observable only near level crossings involving strong Coriolis and α interactions. The energy structure within these perturbers is severely complicated by strong Coriolis and α resonances and by ? (2, 2), ? (2,−1), and ? (2,−4) interactions as already revealed by the ν₂(A₁, 710.16 cm⁻¹) and ν₅ (E, 701.72 cm⁻¹) fundamentals. Interactions of the perturbing states with the ν₁/ν₄ dyad are particularly evident in local crossings. In total, 12 transitions belonging to the dark states and 68 perturbation-allowed transitions within the ν₁/ν₄ dyad have been detected among the more than 5000 transitions that have been assigned for the ν₁/ν₄ dyad, with J_max and K_max of 50 and 30, respectively. Altogether about 85% of the assigned transitions were fitted with a standard deviation of 0.221×10⁻³ cm⁻¹, leading to 61 parameters of the interacting polyad.     

The ν1 and 3ν1 bands of HNCO

The infrared absorption of HNCO has been measured in the region of the NH stretching fundamental and in that of the second overtone. The results for the excited states are (in cm^?1):

     

11.

FTIR Study of the ν₁/ν₄ Bands of D₃SiCl near 1600 cm     

K. AkkadN.Ben Sari-Zizi  H. BürgerE.B. MKadmi 《Journal of Molecular Spectroscopy》2002,213(1):35-45

The ν₁ (A₁, 1583.22 cm⁻¹) and ν₄ (E, 1615.33 cm⁻¹) Si-D stretching bands of monoisotopic D₃Si³⁵Cl have been studied by FTIR spectroscopy with a resolution of 3.3×10⁻³ cm⁻¹. We have assigned 2341 rovibrational lines for ν₁ (J_max=70, K_max=19) and 6207 for ν₄ (J_max=75, K_max=27). Both (ΔK=±1, Δ?=±1) and (ΔK=±2, Δ?=?1) interactions connect the v₁=1 and v₄=1 levels, the latter exerting moreover a weak ?(2, 2) interaction. These interactions were taken into account in a nonlinear least-squares fit, refining 29 free parameters with a standard deviation of 0.257×10⁻³ cm⁻¹ over 6722 nonzero-weighted data. Blended lines and about 250 of the 330 lines belonging to the K=11 subband of ν₁ and the KΔK=−6 subband of ν₄ were zero-weighted because they are locally perturbed respectively by the neighboring upper states of the 2ν₃+ν₆ (E, 1561.95 cm⁻¹) and 3ν₃ (A₁, 1604.81 cm⁻¹) bands. Equivalent fits were obtained for altogether three different models obeying constraints according to the theory of unitary equivalent reductions of the rovibrational Hamiltonian. By means of a band contour simulation both the transition moment ratio |M₁:M₄|=0.67 and a positive sign of the Coriolis intensity perturbation were determined.     

12.

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.     

13.

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.     

14.

Microwave and Submillimeter-Wave Measurements of HDCO in the ν₄, ν₅, and ν₆ Bands: Evidence of Vibrational Induced Rotational Axis Switching (“VIRAS”)     

A PerrinJ.-M Flaud  L MargulèsJ Demaison  H MäderS Wörmke 《Journal of Molecular Spectroscopy》2002,216(2):214-224

The rotational spectrum of HDCO in the 4¹, 5¹, and 6¹ excited vibrational states has been investigated in Lille and Kiel using a sample enriched in deuterium. In Lille, the measurements were performed in the millimeter region (160-600 GHz). The spectra in Kiel were recorded using Fourier transform microwave spectrometers in the regions around 8-18 and 18-26 GHz, employing a rectangular waveguide of length 12 m and a circular waveguide of length 36 m, respectively. These results were combined with the 4¹, 5¹, and 6¹ infrared energy levels which were obtained from a previous analysis of FTS spectra of the ν₄ (CHD bend), ν₅ (CHD rocking), and ν₆ bands (out of plane bend) recorded in the 10-μm region at Giessen (A. Perrin, J.-M. Flaud, M. Smirnov, and M. Lock, J. Mol. Spectrosc.203, 175-187 (2000)). The energy level calculation of the 4¹, 5¹, and 6¹ interacting states accounts for the usual A- and B-type Coriolis resonances in the 5¹⇔6¹ and 4¹⇔6¹ off diagonals blocks. In addition, since the energy levels of the 5¹ and 6¹ states are very strongly resonating, it proved necessary, as in our previous study, to use a {J_x, J_z} nonorthorhombic term in the 5¹ and 6¹v-diagonal blocks of the Hamiltonian matrix in order to reproduce properly the observed microwave transitions and infrared energy levels. Therefore, this work confirms that HDCO is a good example of the vibrational induced rotational axis switching (“VIRAS”) effect.     

15.

High-Resolution Infrared Study of the ν₁₁ Band of Allene     

S NissenF Hegelund  M.S JohnsonB Nelander 《Journal of Molecular Spectroscopy》2002,216(2):197-202

The high-resolution infrared spectrum of allene has been observed in the 280-380 cm⁻¹ region at a nominal resolution of 0.00125 cm⁻¹ using the IR beamline at the MAX-I electron storage ring in Lund. The spectrum shows the bending fundamental of the ν₁₁ band from which spectroscopic constants for the ν₁₁ level have been obtained. The accompanying hot band component 2ν₁₁²-ν₁₁¹ has also been assigned and analyzed.     

16.

First Gas Phase Infrared Spectroscopy of F₂BOH: High-Resolution Study of the ν₈ and ν₉ Bands     

D. ColletA. Perrin  H. BürgerJ.-M. Flaud 《Journal of Molecular Spectroscopy》2002,212(1):118-124

For the first time the infrared spectrum of F₂BOH in the gas phase has been observed. After optimizing the conditions for the synthesis we have been able to obtain high-resolution (2.4-3.3×10⁻³ cm⁻¹) infrared spectra in the ν₈, ν₉, and ν₄ regions with both natural and ¹¹B monoisotopic material. Analyses of the ν₈ (BF₂ out-of-plane bending) and ν₉ (OH torsion) fundamental bands located at 684.160 and 522.870 cm⁻¹, respectively, for F₂¹¹BOH are presented here. Existing J≤10 microwave transitions were combined with novel ground state combination differences with J≤55 formed from A-type (ν₄) and C-type (ν₈, ν₉) bands to yield substantially improved and extended ground state parameters. Using a standard Watson-type Hamiltonian, 8¹ and 9¹ upper state parameters were obtained by fitting about 2000 lines each with σ(fit) ca. 3.5×10⁻⁴ cm⁻¹. The 8¹ and 9¹ states both appear to be unperturbed, as indicated by the agreement of the ground and excited state centrifugal distortion constants.     

17.

A multispectrum analysis of the ν₄ band of CH₄: Widths, shifts, and line mixing coefficients     

M.A.H. Smith  D. Chris Benner  V. Malathy Devi 《Journal of Quantitative Spectroscopy & Radiative Transfer》2011,112(6):952-968

Line positions, Lorentz air-broadened half width and air pressure-induced shift coefficients have been measured for nearly 200 transitions in the ν₄ band of ¹³CH₄ from high-resolution spectra recorded with the McMath-Pierce Fourier transform spectrometer. Three room temperature spectra of ¹³CH₄ used in the previous study of Malathy Devi et al. (Air-broadened Lorentz halfwidths and pressure-induced line shifts in the ν₄ band of ¹³CH₄. Appl. Opt. 1988; 27: 2296-2308) were analyzed together with a large number of additional spectra of self- and air-broadened CH₄ recorded at 210-314 K and one room-temperature spectrum of self-broadened ¹³CH₄. Analyses applying the multispectrum nonlinear least squares fitting technique were performed to retrieve the spectral line parameters. In addition to air-broadened half width and shift coefficients, self-broadened half width and shift coefficients were determined for at least 56 ¹³CH₄ ν₄ transitions. Off-diagonal relaxation matrix element coefficients for air-broadened line mixing were also determined for 28 pairs of P and R transitions in a number of J manifolds, and mixing parameters for self-broadening were also determined for some of these pairs. Temperature-dependences of the pressure-induced shift and mixing parameters for the ¹³CH₄ lines could not be determined from the spectra used in the present analysis, but temperature dependences of the half width coefficients were determined for the strongest transitions. The results of this study are compared with other studies of air- and self-broadened ¹³CH₄ and ¹²CH₄.     

18.

Water Spectra in the Region 4200-6250 cm, Extended Analysis of ν₁+ν₂, ν₂+ν₃, and 3ν₂ Bands and Confirmation of Highly Excited States from Flame Spectra and from Atmospheric Long-Path Observations     

S.N. Mikhailenko  VL.G. TyuterevV.I. Starikov  K.K. AlbertB.P. Winnewisser  M. Winnewisser  G. MellauC. Camy-Peyret  R. LanquetinJ.-M. Flaud  J.W. Brault 《Journal of Molecular Spectroscopy》2002,213(2):91-121

Water vapor infrared spectra have been recorded at room temperature in the range 4200-6250 cm⁻¹ at resolutions (FWHM) between 0.0053 and 0.0080 cm⁻¹. The use of a White-type multireflection cell made large pressure × pathlength products possible up to 31.27 mbar×288.5 m. The high signal-to-noise ratio allowed us to observe lines with intensities as small as 10⁻²⁶ cm⁻¹/molecule cm⁻² at T=296 K. Among about 5100 recorded water lines, about half of which are reported for the first time, 2351 lines have been assigned to the second triad of H₂¹⁶O (bands ν₁+ν₂, ν₂+ν₃, and 3ν₂). This has allowed the determination of line positions and corresponding upper rovibrational states with considerably improved accuracy. The assignments of certain highly excited states have been confirmed by the analysis of flame spectra and hot emission spectra. New values of effective Hamiltonian parameters for the upper states {(110), (030), (011)} have been determined. The generating function model was used in the data reduction to account for the anomalously strong centrifugal distortion of the rovibrational levels and resonance interactions. The RMS standard deviation of the least-squares fit of the assigned H₂O data was 5×10⁻³ cm⁻¹ for line positions and 7×10⁻³ cm⁻¹ for energy levels up to J_max=20 and K_a(max)=13. Particular attention was paid to water lines in the transparency window 4200-5000 cm⁻¹, in which existing databases are not sufficient. In this region, 1395 lines of four isotopic species of water have been recorded and over 900 accurate line positions of nine bands of H₂¹⁶O (ν₁, ν₃, 2ν₂, ν₁+ν₂, ν₂+ν₃, 3ν₂, 4ν₂−ν₂, 2ν₂+ν₃−ν₂, ν₁+2ν₂−ν₂) are reported in this range. A comparison of laboratory spectra with long path atmospheric spectra (20 km slant path in the mountains) in this region shows that many lines missing from available spectroscopic compilations (or considerably shifted compared to observations) are important for a proper interpretation of atmospheric observations. A comparison of the observed data with the best available predictions from the molecular electronic potential energy surface is discussed.     

19.

Diode Laser Spectrum of the ν₁ Fundamental Band of PNO     

Yuyan LiuP.A. Hamilton  P.B. Davies 《Journal of Molecular Spectroscopy》2002,211(1):107-109

The diode laser spectrum of the ν₁ fundamental band of the short-lived molecule PNO has been detected with 59 R- and P-branch lines accurately measured. The lines were unambiguously assigned using the rotational and distortion constants for the ground and (100) vibrational levels found previously by microwave spectroscopy. The band origin was determined to be 860.301 228(31) cm⁻¹ from a one parameter fit. The gas phase band origin is red-shifted by approximately 4 cm⁻¹ from the matrix value.     

20.

DFT molecular structure and initial assignment for the FTIR spectrum of ν₇ band of nitromethane-D₃     

Chandramadhab Pal  R. J. Kshirsagar 《Indian Journal of Physics》2010,84(8):929-937

The preliminary analysis of the DFT calculations and the high-resolution Fourier transform spectrum of the ν₇ band of CD₃NO₂ have been carried out for the first time. The rotational structure up to J = 10 have been fitted using Watson’s A-reduction in I ^r representation with a standard deviation of 0.0048cm⁻¹. The rotational constants A, B, C have been obtained for the ν₇ state of CD₃NO₂ with good statistical significance.     

Band	$\text{ν}{}_0$	$\text{A-}\text{B}$	B	C
$\text{ν}{}_1$	3533.1	27.0	—	—
$\text{3ν}{}_1$	10145.79	22.6713	0.368426	0.361722

FTIR Study of the ν1/ν4 Bands of D3SiCl near 1600 cm

The ν₁ (A₁, 1583.22 cm⁻¹) and ν₄ (E, 1615.33 cm⁻¹) Si-D stretching bands of monoisotopic D₃Si³⁵Cl have been studied by FTIR spectroscopy with a resolution of 3.3×10⁻³ cm⁻¹. We have assigned 2341 rovibrational lines for ν₁ (J_max=70, K_max=19) and 6207 for ν₄ (J_max=75, K_max=27). Both (ΔK=±1, Δ?=±1) and (ΔK=±2, Δ?=?1) interactions connect the v₁=1 and v₄=1 levels, the latter exerting moreover a weak ?(2, 2) interaction. These interactions were taken into account in a nonlinear least-squares fit, refining 29 free parameters with a standard deviation of 0.257×10⁻³ cm⁻¹ over 6722 nonzero-weighted data. Blended lines and about 250 of the 330 lines belonging to the K=11 subband of ν₁ and the KΔK=−6 subband of ν₄ were zero-weighted because they are locally perturbed respectively by the neighboring upper states of the 2ν₃+ν₆ (E, 1561.95 cm⁻¹) and 3ν₃ (A₁, 1604.81 cm⁻¹) bands. Equivalent fits were obtained for altogether three different models obeying constraints according to the theory of unitary equivalent reductions of the rovibrational Hamiltonian. By means of a band contour simulation both the transition moment ratio |M₁:M₄|=0.67 and a positive sign of the Coriolis intensity perturbation were determined.     

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.     

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.     

Microwave and Submillimeter-Wave Measurements of HDCO in the ν4, ν5, and ν6 Bands: Evidence of Vibrational Induced Rotational Axis Switching (“VIRAS”)

The rotational spectrum of HDCO in the 4¹, 5¹, and 6¹ excited vibrational states has been investigated in Lille and Kiel using a sample enriched in deuterium. In Lille, the measurements were performed in the millimeter region (160-600 GHz). The spectra in Kiel were recorded using Fourier transform microwave spectrometers in the regions around 8-18 and 18-26 GHz, employing a rectangular waveguide of length 12 m and a circular waveguide of length 36 m, respectively. These results were combined with the 4¹, 5¹, and 6¹ infrared energy levels which were obtained from a previous analysis of FTS spectra of the ν₄ (CHD bend), ν₅ (CHD rocking), and ν₆ bands (out of plane bend) recorded in the 10-μm region at Giessen (A. Perrin, J.-M. Flaud, M. Smirnov, and M. Lock, J. Mol. Spectrosc.203, 175-187 (2000)). The energy level calculation of the 4¹, 5¹, and 6¹ interacting states accounts for the usual A- and B-type Coriolis resonances in the 5¹⇔6¹ and 4¹⇔6¹ off diagonals blocks. In addition, since the energy levels of the 5¹ and 6¹ states are very strongly resonating, it proved necessary, as in our previous study, to use a {J_x, J_z} nonorthorhombic term in the 5¹ and 6¹v-diagonal blocks of the Hamiltonian matrix in order to reproduce properly the observed microwave transitions and infrared energy levels. Therefore, this work confirms that HDCO is a good example of the vibrational induced rotational axis switching (“VIRAS”) effect.     

High-Resolution Infrared Study of the ν11 Band of Allene

The high-resolution infrared spectrum of allene has been observed in the 280-380 cm⁻¹ region at a nominal resolution of 0.00125 cm⁻¹ using the IR beamline at the MAX-I electron storage ring in Lund. The spectrum shows the bending fundamental of the ν₁₁ band from which spectroscopic constants for the ν₁₁ level have been obtained. The accompanying hot band component 2ν₁₁²-ν₁₁¹ has also been assigned and analyzed.     

First Gas Phase Infrared Spectroscopy of F2BOH: High-Resolution Study of the ν8 and ν9 Bands

For the first time the infrared spectrum of F₂BOH in the gas phase has been observed. After optimizing the conditions for the synthesis we have been able to obtain high-resolution (2.4-3.3×10⁻³ cm⁻¹) infrared spectra in the ν₈, ν₉, and ν₄ regions with both natural and ¹¹B monoisotopic material. Analyses of the ν₈ (BF₂ out-of-plane bending) and ν₉ (OH torsion) fundamental bands located at 684.160 and 522.870 cm⁻¹, respectively, for F₂¹¹BOH are presented here. Existing J≤10 microwave transitions were combined with novel ground state combination differences with J≤55 formed from A-type (ν₄) and C-type (ν₈, ν₉) bands to yield substantially improved and extended ground state parameters. Using a standard Watson-type Hamiltonian, 8¹ and 9¹ upper state parameters were obtained by fitting about 2000 lines each with σ(fit) ca. 3.5×10⁻⁴ cm⁻¹. The 8¹ and 9¹ states both appear to be unperturbed, as indicated by the agreement of the ground and excited state centrifugal distortion constants.     

A multispectrum analysis of the ν4 band of CH4: Widths, shifts, and line mixing coefficients

Line positions, Lorentz air-broadened half width and air pressure-induced shift coefficients have been measured for nearly 200 transitions in the ν₄ band of ¹³CH₄ from high-resolution spectra recorded with the McMath-Pierce Fourier transform spectrometer. Three room temperature spectra of ¹³CH₄ used in the previous study of Malathy Devi et al. (Air-broadened Lorentz halfwidths and pressure-induced line shifts in the ν₄ band of ¹³CH₄. Appl. Opt. 1988; 27: 2296-2308) were analyzed together with a large number of additional spectra of self- and air-broadened CH₄ recorded at 210-314 K and one room-temperature spectrum of self-broadened ¹³CH₄. Analyses applying the multispectrum nonlinear least squares fitting technique were performed to retrieve the spectral line parameters. In addition to air-broadened half width and shift coefficients, self-broadened half width and shift coefficients were determined for at least 56 ¹³CH₄ ν₄ transitions. Off-diagonal relaxation matrix element coefficients for air-broadened line mixing were also determined for 28 pairs of P and R transitions in a number of J manifolds, and mixing parameters for self-broadening were also determined for some of these pairs. Temperature-dependences of the pressure-induced shift and mixing parameters for the ¹³CH₄ lines could not be determined from the spectra used in the present analysis, but temperature dependences of the half width coefficients were determined for the strongest transitions. The results of this study are compared with other studies of air- and self-broadened ¹³CH₄ and ¹²CH₄.     

Water Spectra in the Region 4200-6250 cm, Extended Analysis of ν1+ν2, ν2+ν3, and 3ν2 Bands and Confirmation of Highly Excited States from Flame Spectra and from Atmospheric Long-Path Observations

Water vapor infrared spectra have been recorded at room temperature in the range 4200-6250 cm⁻¹ at resolutions (FWHM) between 0.0053 and 0.0080 cm⁻¹. The use of a White-type multireflection cell made large pressure × pathlength products possible up to 31.27 mbar×288.5 m. The high signal-to-noise ratio allowed us to observe lines with intensities as small as 10⁻²⁶ cm⁻¹/molecule cm⁻² at T=296 K. Among about 5100 recorded water lines, about half of which are reported for the first time, 2351 lines have been assigned to the second triad of H₂¹⁶O (bands ν₁+ν₂, ν₂+ν₃, and 3ν₂). This has allowed the determination of line positions and corresponding upper rovibrational states with considerably improved accuracy. The assignments of certain highly excited states have been confirmed by the analysis of flame spectra and hot emission spectra. New values of effective Hamiltonian parameters for the upper states {(110), (030), (011)} have been determined. The generating function model was used in the data reduction to account for the anomalously strong centrifugal distortion of the rovibrational levels and resonance interactions. The RMS standard deviation of the least-squares fit of the assigned H₂O data was 5×10⁻³ cm⁻¹ for line positions and 7×10⁻³ cm⁻¹ for energy levels up to J_max=20 and K_a(max)=13. Particular attention was paid to water lines in the transparency window 4200-5000 cm⁻¹, in which existing databases are not sufficient. In this region, 1395 lines of four isotopic species of water have been recorded and over 900 accurate line positions of nine bands of H₂¹⁶O (ν₁, ν₃, 2ν₂, ν₁+ν₂, ν₂+ν₃, 3ν₂, 4ν₂−ν₂, 2ν₂+ν₃−ν₂, ν₁+2ν₂−ν₂) are reported in this range. A comparison of laboratory spectra with long path atmospheric spectra (20 km slant path in the mountains) in this region shows that many lines missing from available spectroscopic compilations (or considerably shifted compared to observations) are important for a proper interpretation of atmospheric observations. A comparison of the observed data with the best available predictions from the molecular electronic potential energy surface is discussed.     

Diode Laser Spectrum of the ν1 Fundamental Band of PNO

The diode laser spectrum of the ν₁ fundamental band of the short-lived molecule PNO has been detected with 59 R- and P-branch lines accurately measured. The lines were unambiguously assigned using the rotational and distortion constants for the ground and (100) vibrational levels found previously by microwave spectroscopy. The band origin was determined to be 860.301 228(31) cm⁻¹ from a one parameter fit. The gas phase band origin is red-shifted by approximately 4 cm⁻¹ from the matrix value.     

DFT molecular structure and initial assignment for the FTIR spectrum of ν7 band of nitromethane-D3

The preliminary analysis of the DFT calculations and the high-resolution Fourier transform spectrum of the ν₇ band of CD₃NO₂ have been carried out for the first time. The rotational structure up to J = 10 have been fitted using Watson’s A-reduction in I ^r representation with a standard deviation of 0.0048cm⁻¹. The rotational constants A, B, C have been obtained for the ν₇ state of CD₃NO₂ with good statistical significance.