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.     

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.     

New High-Resolution Analysis of the ν7 and ν9 Fundamental Bands of trans-Formic Acid by Fourier Transform Infrared and Millimeter-Wave Spectroscopy

The high-resolution (0.002 cm⁻¹) spectrum of the ν₇ (OCO scissor mode) and ν₉ (COH torsion mode) fundamental bands of trans-formic acid (HCOOH) at 15.8 μm was recorded by Fourier transform infrared spectroscopy. In addition, millimeter-wave transitions within the 7¹ and 9¹ vibrational states were measured in the spectral range 340-600 GHz. Using these new experimental data, an extensive analysis of the ν₇ and ν₉ bands was performed. The model we have used accounts for the strong A- and B-type Coriolis interactions which couple the 7¹ and 9¹ vibrational states and which were already pointed out in the literature [J. C. Deroche, J. Kauppinen and E. Kyrö, J. Mol. Spectrosc.78, 379-394 (1979); E. Willemot, J. Mol. Spectrosc.120, 246-275 (1986)]. The observed levels are fit to within the experimental accuracy leading to the determination of a precise set of band centers of ν₇ and ν₉ at 686.1656 cm⁻¹ and 640.7251 cm⁻¹, respectively, and rotational and Coriolis constants.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

High-Resolution Infrared Study of PHD2: The P-H Stretching Bands ν1 and 2ν1

For the first time the infrared spectrum of PHD₂ was recorded in the region of the PH stretching fundamental ν₁ at 2324.005 cm⁻¹ and the overtone 2ν₁ at 4563.634 cm⁻¹ with a resolution of 4.2×10⁻³ cm⁻¹ and 8.8×10⁻³ cm⁻¹, respectively. In the analyses about 1340 and 1020 transitions were assigned to the corresponding ν₁ and 2ν₁ bands, which provided 316 and 248 upper energies, respectively. Since both the bands are sufficiently isolated, a standard Watson-type Hamiltonian (A-reduction, I^r-representation) was employed. The obtained sets of spectroscopic parameters correlate very well both with each other, and with the corresponding parameters of the ground vibrational state.     

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.     

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.     

A Combined Frequency Analysis of the ν3, ν9, 3ν4 and the Far-Infrared Bands of Ethane: A Reassessment of the Torsional Parameters for the Ground Vibrational State

The lowest frequency parallel fundamental band ν₃ of ethane is Raman active. A stimulated Raman spectrum of the Q branch for this band at a resolution of 0.0055 cm⁻¹ has been measured by D. Bermejo et al. (1992, J. Chem. Phys.97, 7055). The torsion-rotation series in this band with σ=3, where σ=0, 1, 2, and 3 labels the torsional sublevels, is perturbed by over 1 cm⁻¹. The lowest frequency-degenerate fundamental ν₉ is infrared active. A high-resolution (0.0014 cm⁻¹) Fourier transform spectrum of this band has been measured by N. Moazzen-Ahmadi et al. (1999, J. Chem. Phys.111, 9609). The observed torsional splittings for this band are substantially larger than expected from the observed barrier height. Because of a near-degeneracy of the upper level in the ν₉ band with its interacting partner (v₉=0, v₄=3) a perturbation allowed band 3ν₄ has also been observed. We have carried out a combined analysis of ν₃, ν_9, and 3ν₄ together with the far-infrared torsional spectra in the ground vibrational state (gs). A fit to within the experimental error was achieved using 37 parameters. The large torsional splittings in the ν₉ band are attributed to Coriolis-type interactions between the torsional stacks of gs and v₉=1 whereas the large shift for the torsion-rotation series with σ=3 in the ν₃ band is attributed to Fermi-type interactions between the torsional stacks of the gs and v₃=1. The introduction of the Fermi-type interactions causes a considerable change in the leading terms in the torsional Hamiltonian for the gs. These changes are quantitatively explained.     

Analysis of the High-Resolution Infrared Spectrum of the PHD2 Molecule: ν1 and 2ν1 Bands

The results of investigation into the infrared spectra of the PHD₂ molecule including the ₁ fundamental band centered at 2324.005 cm^–1 (with a resolution of 4.2·10^–3 cm^–1) and the first 2₁ valence overtone centered at 4563.634 cm^–1 (with a resolution of 8.8·10^–3 cm^–1) are given in the present paper. Based on an analysis of the results obtained, 1340 and 1020 lines are referred to the ₁ and 2₁ bands, respectively. This data are used to calculate 316 and 248 vibrational-rotational energies of the (100000) and (200000) excited vibrational states, respectively. Since both bands can be considered as isolated, we take advantage of the Watson Hamiltonian (the reduction A in the I ^r representation) to describe their rotational structure. The calculated spectroscopic parameters of the examined states of the PHD₂ molecule correlate well with each other and with the corresponding parameters of the ground vibrational state.     

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):

     

20.

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

F. WintherM. Schönhoff  A. Huckauf  E.B. Mkadmi 《Journal of Molecular Spectroscopy》2002,216(2):374-378

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.     

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

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.