High-Resolution Infrared Spectra of the ν2, ν3, ν4, and 2ν3 Bands of SO3

New measurements are reported for the infrared spectrum of sulfur trioxide, ³²S¹⁶O₃, with resolutions ranging from 0.0015 cm⁻¹ to 0.0025 cm⁻¹. Rovibrational constants have been measured for the fundamentals ν₂, ν₃, and ν₄ and the overtone band 2ν₃. Comparisons are made with the earlier high-resolution measurements on SO₃, and the high correlation among some of the constants related to the Coriolis coupling of the ν₂ and ν₄ levels is discussed in order to understand the areas of disagreement with the earlier work. Splittings of some of the levels are observed and the splitting constant for K=3 of the ground state is determined for the first time. Other observed splittings include the K=1 levels of 2ν₃ (l=2), the K=2 levels of ν₃ and ν₄, and the K=3 levels of ν₂. The analysis shows that there are level crossings between the l=0 and l=2 states of 2ν₃ that allow one to determine the separation of the subband centers for these two states even though access to the l=0 state from the ground state is electric-dipole forbidden. This is a generalized phenomenon that should be found for many other molecules with the same symmetry. The l-type resonance constant, q₃, that causes the splitting of the l₃=±1, k=±1 levels of ν₃ also couples the l₃=0 and 2 states of 2ν₃.     

High-Resolution Infrared Spectroscopy of Methyl Isocyanide: The ν3, ν6, and ν7 + ν8 Bands

The vibration-rotation spectrum of methyl isocyanide (CH₃NC) has been recorded with the aid of a high-resolution Fourier transform spectrometer in the region 1370 to 1560 cm⁻¹ containing the perpendicular band of the fundamental vibration ν₆ (species E), the weaker parallel band of the ν₃ (A₁) fundamental, and the perpendicular combination band ν₇ + ν₈ (E) enhanced by Fermi resonance with ν₆. Sixteen hundred seventy well-resolved lines were assigned to 15 subbands of ν₆, 6 subbands of ν₃, and 3 subbands of ν⁻₇ + ν⁻₈. A strong x, y-Coriolis resonance between ν₃ and ν₆ and Fermi resonance between ν^±₆ and the E component ν₇ + ν₈, as well as between ν₃ and the A_1,2 components ν^±₇ + ν₈, greatly affects the spectrum. Additional weaker anharmonic interaction of ν₆ with the ν₄ + 2ν²₈ combination and higher-order rotational interactions connecting the various states were also detected in the spectrum. All of these interactions have been incorporated into a 9 × 9 Hamiltonian matrix used for modeling the upper states of the observed transitions. A set of spectroscopic constants is reported for the upper states of the bands ν₃, ν₆, and ν₇ + ν₈ and for ν₄ + 2ν²₈ which reproduces the observed lines with an overall standard deviation of 0.0012 cm⁻¹.     

Line Positions and Intensities of the ν1+ ν2+ 3ν3, ν2+ 4ν3, and 3ν1+ 2ν2Bands of Ozone

Using a Fourier transform spectrometer, we have recorded the spectra of ozone in the region of 4600 cm⁻¹, with a resolution of 0.008 cm⁻¹. The strongest absorption in this region is due to the ν₁+ ν₂+ 3ν₃band which is in Coriolis interaction with the ν₂+ 4ν₃band. We have been able to assign more than 1700 transitions for these two bands. To correctly reproduce the calculation of energy levels, it has been necessary to introduce the (320) state which strongly perturbs the (113) and (014) states through Coriolis- and Fermi-type resonances. Seventy transitions of the 3ν₁+ 2ν₂band have also been observed. The final fit on 926 energy levels withJ_max= 50 andK_max= 16 gives RMS = 3.1 × 10⁻³cm⁻¹and provides a satisfactory agreement of calculated and observed upper levels for most of the transitions. The following values for band centers are derived: ν₀(ν₁+ ν₂+ 3ν₃) = 4658.950 cm⁻¹, ν₀(3ν₁+ 2ν₂) = 4643.821 cm⁻¹, and ν₀(ν₂+ 4ν₃) = 4632.888 cm⁻¹. Line intensities have been measured and fitted, leading to the determination of transition moment parameters for the two bands ν₁+ ν₂+ 3ν₃and ν₂+ 4ν₃. Using these parameters we have obtained the following estimations for the integrated band intensities,S_V(ν₁+ ν₂+ 3ν₃) = 8.84 × 10⁻²²,S_V(ν₂+ 4ν₃) = 1.70 × 10⁻²², andS_V(3ν₁+ 2ν₂) = 0.49 × 10⁻²²cm⁻¹/molecule cm⁻²at 296 K, which correspond to a cutoff of 10⁻²⁶cm⁻¹/molecule cm⁻².     

The FT-IR Spectrum of HCNO: The ν1, ν2, 2ν3, and ν2 + ν3 Band Systems

The infrared spectrum of HC¹⁵NO an isotopically substituted species of fulminic acid, has been measured in the range 1900-3600 cm⁻¹ at a resolution of 0.003 cm⁻¹ with a Bruker IFS 120 HR interferometer. More than 100 subbands have been assigned. Power series coefficients for these transitions are given. A Coriolis resonance between the levels 01002 (l = 0e) and 01010 (l = 1e) allows normally "forbidden" transitions to occur, some of which were observed and assigned. We correlate transition intensities and energies of the resonance system. Variations in the manifold of nν₅ states with excitation of other modes are compared.     

A High-Resolution Fourier Transform Infrared Study of the ν3, ν4, and ν5 Bands of Deuterated Formyl Chloride (DCOCl)

High-resolution infrared spectra of the low-lying ν₃, ν₄, and ν₅ fundamentals of the transient molecule DCOCl are reported. These type-A/B hybrid bands have been analyzed in detail, providing extensive rotational assignments for the DCO³⁵Cl and DCO³⁷Cl isotopomers. The ground state constants have been refined by a simultaneous fit of the available microwave data and FTIR combination differences from the three bands. The excited state constants have been determined by fitting assignments over a wide range of J and K_a values. A small perturbation was found at high K_a values in the ν₄ band and determined to be due to a ΔK_a = −2 interaction with the rotational levels of the 6¹ vibrational state.     

CO2: Global Treatment of Vibrational–Rotational Spectra and First Observation of the 2ν1 + 5ν3 and ν1 + 2ν2 + 5ν3 Absorption Bands

The effective operator approach is applied to the calculation of both line positions and line intensities of the ¹³C¹⁶O₂ molecule. About 11 000 observed line positions of ¹³C¹⁶O₂ selected from the literature have been used to derive 84 parameters of a reduced effective Hamiltonian globally describing all known vibrational–rotational energy levels in the ground electronic state. The standard deviation of the fit is 0.0015 cm⁻¹. The eigenfunctions of this effective Hamiltonian have then been used in fittings of parameters of an effective dipole-moment operator to more than 600 observed line intensities of the cold and hot bands covering the ν₂ and 3ν₂ regions. The standard deviations of the fits are 3.2 and 12.0% for these regions, respectively. The quality of the fittings and the extrapolation properties of the fitted parameters are discussed. A comparison of calculated line parameters with those provided by the HITRAN database is given. Finally, the first observations of the 2ν₁ + 5ν₃ and ν₁ + 2ν₂ + 5ν₃ absorption bands by means of photoacoustic spectroscopy (PAS) is presented. The deviations of predicted line positions from observed ones is found to be less than 0.1 cm⁻¹, and most of them lie within the experimental accuracy (0.007 cm⁻¹) once the observed line positions are included in the global fit.     

Analysis of the ν1 + ν2 + ν3 band of O3

The high resolution spectrum of the ν₁ + ν₂ + ν₃ band of O₃ in the 2800-cm⁻¹ region has been analyzed using Watson's Hamiltonian. The resulting Hamiltonian constants and previously published line intensities have been used to generate a listing of line assignments, positions, absolute intensities, and ground state energies. These should be useful for atmospheric studies.     

The ν1 and 2ν1 bands of DNSO

The infrared spectrum of DNSO has been recorded in the region of the N-D stretching fundamental vibration and of the first overtone. The results of the analysis are the following (in cm⁻¹):

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Analysis of the Coriolis-coupled band system of ν5, ν2, and 2ν3 of methyl-d3 iodide

The Coriolis-coupled band system of ν₅, ν₂, and 2ν₃ of CD₃I was analyzed by making use of all of the experimental data now available. These data included the high-resolution infrared spectra, microwave spectra, and laser Stark spectra. The analysis gave values, more precise than before, of the spectroscopic constants for ν₅, ν₂, and 2ν₃ and the interaction constants. The determination of the rotational constant A for 2ν₃ gave a value for , with which all of the α^A constants for CD₃I have been completed. These α^A values were incorporated with the known value of A₆ to give a value for A₀.     

Line Intensities in the ν1, ν3, and 2ν2 Bands of H2Se

Using a high-resolution Fourier transform spectrum of hydrogen selenide in natural abundance, about 600 intensities of lines belonging to the ν₁, ν₃, and 2ν₂ bands of H₂⁸⁰Se were measured. A least-squares fit of these intensities was performed, allowing determination of the vibrational transition moments of these bands and their rotational corrections. Finally, the first derivatives of the dipole moment with respect to the normal coordinates q₁ and q₃ were found to be ∂μ_χ/∂q₁ = (−0.5938 ± 0.010) × 10⁻¹ and ∂μ_z/∂q₃ = (0.5683 ± 0.010) × 10⁻¹ Debye, respectively.     

Line positions and intensities for the ν1 + ν2 and ν2 + ν3 bands of H2O

The intensities of about 90 lines of the ν₁ + ν₂ and ν₂ + ν₃ bands of H₂¹⁸O have been measured using a Fourier transform spectrum of natural water vapor. The constants involved in the rotational expansion of the transformed transition moment operators corresponding to these bands have been determined through a fit of these line intensities. The constants obtained are used to compute the whole spectrum of the ν₁ + ν₂ and ν₂ + ν₃ bands of H₂¹⁸O providing reliable line positions and intensities. For lines involving perturbed levels a comparison is given with the results obtained for H₂¹⁶O and it is shown that the results for one isotopic species cannot be transferred directly to another one.     

The ν2, ν5 Raman band system of CH3F

The anisotropic and isotropic components of the ν₂, ν₅ rotation-vibrational Raman bands of ¹³CH₃F were obtained separately. The two upper states are coupled by a strong second-order Coriolis resonance. The anisotropic spectrum was analyzed by means of a program system due to R. Escribano. A contour simulation and a least-squares fit of 233 assigned transitions yielded values for ν₅, ΔA₅, ΔA₂, and Aζ_{5a, 5b^(z)}. The ¹³C shifts of ν₂ and ν₅ were obtained from the isotropic spectrum.     

The ν2 and 2ν2 - ν2 bands of N O2: Electron Spin-Rotation and Hyperfine Contact Resonances in the (010) Vibrational State

High-resolution Fourier transform spectra covering the 720-920 cm⁻¹ spectral region have been used to perform a reanalysis of the ν₂ band ((010)-(000) vibrational transition) together with the first analysis of the 2ν₂ - ν₂ hot band of nitrogen dioxide ((020)-(010) vibrational transition). The high-quality spectra show that, for numerous ν₂ lines, the hyperfine structure is easily observable in the case of resonances due to the hyperfine Fermi-type operator. By performing a full treatment of the spin-rotation and of the hyperfine operators, a new line list of the ν₂ band (positions and intensities) has been generated, and it is in excellent agreement with the experimental spectrum. Also, a thorough analysis of the 2ν₂ - ν₂ hot band has been performed leading to an extended set of new (020) spin-rotation levels. These levels, together with the {(100), (020), (001)} spin-rotation levels deduced previously from the analysis of the ν₁, 2ν₂, and ν₃ cold bands performed in the 6.3- to 7.5-μm spectral range [A. Perrin, J.-M. Flaud, C. Camy-Peyret. A.-M. Vasserot, G. Guelachvili, A. Goldman, F. J. Murcray, and R. D. Blatherwick, J. Mol. Spectrosc.154, 391-406 (1992)] were least-squares fitted, allowing one to derive a new set of vibrational band centers and rotational, spin-rotation, and interaction constants for the {(l00)(020)(001)} interacting states of ¹⁴N ¹⁶O₂.     

The ν1 and ν3 Bands of the OOO Isotopomer of Ozone

Using 0.002 cm⁻¹ resolution Fourier transform absorption spectra of an ¹⁷O-enriched ozone sample, an extensive analysis of the ν₃ band together with a partial identification of the ν₁ band of the ¹⁷O¹⁶O¹⁷O isotopomer of ozone has been performed for the first time. As for other C_2v-type ozone isotopomers [J.-M. Flaud and R. Bacis, Spectrochim. Acta, Part A 54, 3–16 (1998)], the (001) rotational levels are involved in a Coriolis-type resonance with the levels of the (100) vibrational state. The experimental rotational levels of the (001) and (100) vibrational states have been satisfactorily reproduced using a Hamiltonian matrix which takes into account the observed rovibrational resonances. In this way precise vibrational energies and rotational and coupling constants were deduced and the following band centers ν₀(ν₃) = 1030.0946 cm⁻¹ and ν₀(ν₁) = 1086.7490 cm⁻¹ were obtained for the ν₃ and ν₁ bands, respectively.     

The high-resolution infrared spectra of the ν2 and ν3 bands of HOCl

The infrared spectra of the a-type transitions of the ν₂ and ν₃ bands of HO³⁵Cl and HO³⁷Cl have been obtained under high resolution. Line assignments of both bands have been made, and the spectroscopic constants have been obtained for both bands using a Watson Hamiltonian. Lines of the K_a = 5 subband of the ν₂ band of the HO³⁵Cl molecule were found to be slightly shifted by an interaction with the K_a = 4 level of the 2ν₃ vibrational state. The b-type transitions permitted for both bands were too weak to observe. Relative intensities of selected lines of both bands have been measured, and empirical Herman-Wallis factors have been determined.     

High-Resolution Infrared Studies of ν1, 2ν1, and 2ν4 Bands of CHCl3

The C-H stretching fundamental band ν₁ (3033 cm⁻¹) of chloroform CH³⁵Cl₃ has been investigated together with the first overtone 2ν₁ (5941 cm⁻¹) in order to determine the rotation vibration parameters. From the ν₁ band α₁^C=−0.025 46(41)×10⁻³ cm⁻¹ and α₁^B=−0.010 688(44)×10⁻³ cm⁻¹ were obtained. The hot bands connected to the low lying fundamentals ν₃ and ν₆ have been analyzed and anharmonicity constants have been derived. Both the parallel and the perpendicular component band of the C-H bending overtone 2ν₄ have also been studied. In the parallel band (2410 cm⁻¹) more than 900 lines were included in the fit. In the perpendicular band (2443 cm⁻¹) 2615 lines were fitted using a model with one resonance. Among other things the results C₀−C_v=0.025 262 (20)×10⁻³ cm⁻¹, B₀−B_v=0.134 883 (25)×10⁻³ cm⁻¹, and (Cζ)_v=−0.111 867 56 (30) cm⁻¹ were obtained.     

Analysis of the ν9/ν10 band system of allene

The infrared spectrum of allene has been recorded with high resolution (0.002-0.004 cm⁻¹) on a Fourier transform instrument in the region 730 to 1170 cm⁻¹ containing the perpendicular bands, ν₉ and ν₁₀. A total of 21 subbands with KΔK ranging from −6 to +14 have been assigned in the ν₉ band, and 26 subbands with KΔK = −10 to +15 have been assigned in the ν₁₀ band. The bands are affected by a combination of a J_z-Coriolis and a quartic anharmonic interaction between their upper states ν₉ and ν₁₀. In addition, several other more localized perturbations are found in the spectrum. The nature of the interactions responsible for these perturbations is discussed, and five of the strongest perturbations are quantitatively accounted for by constructing a Hamiltonian matrix which includes five different perturbing states and their Coriolis and anharmonic resonances with the ν₉ and ν₁₀ upper states. A set of spectroscopic constants for the ν₉ and ν₁₀ states and for some of the perturbing states is reported.     

The High-Resolution ν5 Band of Jet-Cooled Si2F6

Vibration-rotation spectra of the parallel ν₅ band of hexafluorodisilane have been measured in a supersonic free jet with 0.001 cm⁻¹ resolution. Three isotopic species, ^28,28Si₂F₆, ^28,29Si₂F₆, and ^28,30Si₂F₆, have been studied. The effect of internal rotation is not observed, indicating that the splitting is smaller than our spectral resolution. A very weak parallel band observed with a slight red shift from the ν₅ fundamental band has been assigned tentatively to the (ν₄ + ν₅)-ν₄ hot band.     

IR-spectra of (CO2)2 dimers and collision-induced absorption of carbon dioxide in the region of the fermi doublet (ν1, 2ν2)

The positions and intensities of all vibrational transitions in the (ν₁, 2ν₂) Fermi doublet region of (CO₂)₂ dimers are obtained by means of variational method. The collision-induced absorption in compressed carbon dioxide is shown to be mainly due to dimeric absorption. Assignment of ν₁ and 2ν₂ vibrational bands in isolated CO₂ molecule is performed by consideration of the symmetries and intensities of dimeric vibrations.