Diode laser measurements of the band strengths of ν3 and ν6 in 12CH3D

A diode laser spectrometer has been used to measure line strengths for 143 transitions in the ν₆ fundamental band of ¹²CH₃D near 9 μm. These line-strength measurements have been used to derive a band strength for ν₆ and ν₃. The band strength derived for ν₆ is 61.7 ± 1.8 cm^?2 atm^?1, and that for ν₃ is 49.3 ± 1.4 cm^?2 atm^?1 at 395 K.     

The fundamental band ν2 of D2CO

The ν₂ band of D₂¹³CO in the region of 1570-1760 cm⁻¹ has been analyzed with high accuracy. The limits of the quantum numbers J and K_a are 50 and 16, respectively. The number of the assigned transitions is 3858. A local anharmonic resonance ν₂/2ν₄ at K_a =  8-12 was observed. The Watson’s A-reduced Hamiltonian and anharmonic resonance term were fitted to the observed transitions. The fit resulted in the band center and rotational parameters of the ν₂ band as well as the effective parameters for the 2ν₄ band and anharmonic resonance parameter. The rms deviation of the transitions in the ν₂ band was 0.000364 cm⁻¹.     

The region of the 3ν3 band of methane

The spectrum of methane near 9000 cm^?1, the region of the 3ν₃ band, has been recorded at Meudon Observatory with a Fourier transform spectrometer under high resolution. Intensity measurements at two different temperatures, 149 and 295 K, have allowed us to identify two new vibration bands by determining the lower-state quantum numbers J of the transitions. About 100 lines are now assigned in this range, including P and Q branches. Furthermore, the first detailed rotational analysis of the 3ν₃ band has been made; nine parameters of the band have been determined. The standard deviation of the differences between observed and computed wavenumbers for 45 lines of the 3ν₃ band is only 0.045 cm^?1. It is found that the observed 45 lines of the 3ν₃ band correspond to the sublevel l₃ = 3 and C_v = F₂.     

Analysis of the ν2 + ν3 band of 12CH4 and 13CH4

The ν₂ + ν₃ bands of ¹²CH₄ and ¹³CH₄ occurring in the region 4400–4650 cm^?1 have been studied from spectra recorded with a high-resolution Fourier transform spectrometer (resolution better than 0.01 cm^?1). Champion's Hamiltonian expansion, Canad. J. Phys.55, 1802 (1977), is applied to the problem of the two interacting F₁ and F₂ vibrational sublevels of this type of a band. As the P branch of ν₂ + ν₃ is strongly overlapped by neighboring bands, a combination-difference method, adapted to tetrahedral XY₄ molecules has been developed to help assignments of lines. A fit of 700 transitions has been performed using 13 new effective constants in the case of ¹²CH₄. In the case of ¹³CH₄, 532 transitions have been fit to 18 constants. The known parameters, relative to the vibrational ground state and the ν₃ state for both methanes, and the ν₂ state for ¹²CH₄ were fixed throughout. Most of the perturbed levels, up to J′ = 12, are well reproduced and the general agreement between experimental and calculated transitions is satisfactory with standard deviations of 0.047 cm^?1 (¹²CH₄) and 0.041 cm^?1 (¹³CH₄). The results (order of magnitude of obtained (ν₂ + ν₃) parameters and comparison of observed and computed intensities) indicate that the ν₂ + ν₃ band is perturbed by many other bands.     

Laser Stark spectroscopy of the ν4 band of CH3C15N: Fermi resonance with 3ν83

Laser Stark spectra for the ν₄ band of CH₃C¹⁵N have been measured by using CO₂ and N₂O lasers. Almost 650 resonances have been assigned to about 140 ro-vibrational transitions with J′ ≤ 34 and K ≤ 11. An anomaly of the rotational structure around K = 7 has been proved to be due to a Fermi interaction by analyzing each K subband separately. Observed data have been fitted to a model which includes ν₄-3ν₈³ Fermi coupling by the method of least squares. The standard deviation of observed from calculated frequencies is 4.6 MHz. Molecular constants derived are also listed.     

A simultaneous analysis of the microwave,submillimeterwave, and infrared transitions between the ground and ν2 inversion-rotation levels of 15NH3

The submillimeterwave spectra of the pure inversion and inversion-rotation transitions in the ν₂ excited state (79 transitons) and the diode laser spectra of the ν₂ band (83 transitions) of ¹⁵NH₃ have been measured. A simultaneous least squares analysis has been carried out of these data together with previously published wavenumbers of the pure inversion transitions and inversion-rotation transitions in the ground state measured by the microwave and Fourier spectroscopy, and the ν₂ band transition frequencies obtained by the infrared-microwave two-photon technique. A theory of the Δk = ±3n interactions in the ground and ν₂ excited states of ammonia (?. Urban, V. ?pirko, D. Papou?ek, J. Kauppinen, S. P. Belov, L. I. Gershtein, and A. F. Krupnov, J. Mol. Spectrosc.88, 274–282 (1981)) has been used in the analysis. The “smoothed” values of the ν₂ band wavenumbers can be used for calibration purposes with better than 1 × 10^?3 cm^?1 precision.     

Laser stark spectroscopy of the ν4 + ν8 − ν8 band of CH3C15N: Fermi resonances with 4ν84, 4ν82, and (ν7 + ν8)2

Laser Stark spectra for the ν₄ + ν₈ ? ν₈ parallel band of CH₃C¹⁵N were measured by using CO₂ and N₂O lasers in the 10-μm region. About 300 resonances have been assigned to 102 rovibrational transitions with J′ <- 16 and ?9 ≤ kl ≤ +9. Anomalies observed around kl = ?6 and +8 were proved to be due to the Fermi interactions with 4ν₈² and 4ν₈⁴, respectively. Another Fermi interaction with (ν₇ + ν₈)² was necessary to account for the anomaly around kl = ?6. Observed data were analyzed by the method of least squares, and precise molecular constants have been obtained.     

10-μm sub-doppler laser-Stark spectroscopy of methyl chloride: Analysis of the ν6 bands of the CH335Cl and CH337Cl

About 900 Stark transitions from 70 vibration-rotation transitions in CH₃³⁵Cl and about 400 transitions from 38 transitions in CH₃³⁵Cl in the ν₆ band have been assigned. These data were analyzed simultaneously with previously published microwave data on the ν₆ = 1 state. The fit has a standard deviation of about 2 MHz for the data for both isotopes. The isoptopic shift ν₆35 ? ν₆37 = 0.3766(6) cm^?1. Rotational dependence of the dipole moment was also just apparent at about μ_J = μ_K = 1 × 10^?5 D, and a complete set of molecular constants is given.     

Laser Stark spectroscopy of thioformaldehyde in the 10-μm region: The ν3, ν4, and the ν6 fundamentals

The ν₃, ν₄, and ν₆ bands of thioformaldehyde, H₂CS, have been studied using the technique of laser Stark spectroscopy. The H₂CS was produced by the pyrolysis of dimethyl disulfide, and the spectrum was observed using a multipass absorption cell. The band origins are ν₃, 1059.2037 cm^?1; ν₄, 990.1866 cm^?1; and ν₆, 991.0149 cm^?1. The band previously assigned as 2ν₆ has been reassigned as 2ν₂, leading to a value of the ν₂ band origin of ca. 1439 cm^?1. Rotational constants and dipole moments of the vibrational states have been determined.     

Simultaneous analysis of the microwave and infrared spectra of 14ND3 and 15ND3 for the ν2 excited state

The data on the inversion spectrum in the ν₂ state of ¹⁴ND₃ [F. Scappini, A. Guarnieri, and G. DiLonardo, J. Mol. Spectrosc.95, 20–29 (1982)] have been extended by measuring frequencies of 25 new transitions. A simultaneous least-squares analysis of these data with the ground state microwave transition frequencies and the diode laser measurements of the ν₂ band has been carried out. Improved sets of molecular parameters have been obtained for ¹⁴ND₃ and ¹⁵ND₃, including the ground and ν₂ state inversion splittings, ν₂ band origins, rotational and centrifugal distortion constants, and the parameters of the Δk = ±3n vibrational-rotational interactions.     

Study of the ν2 + ν3 and 2ν6 infrared bands of CH379Br and CH381Br

The rotational analysis of the ν₂ + ν₃ band, centered around 1912 cm^?1, and of both components 2ν₆^±2 and 2ν₆⁰, centered about 1912 and 1904 cm^?1, respectively, has been carried out from a Fourier transform spectrum having a resolution limit of 0.005 cm^?1. A standard deviation of about 0.001 cm^?1 was obtained for about 750 lines of the unperturbed 2ν₆^±2 component for both isotopic species. The ν₂ + ν₃ band, stronger than 2ν₆^±2, is perturbed by two resonances: a Coriolis resonance with the very weak ν₃ + ν₅ band, no line of which has been observed, and an anharmonic resonance with 2ν₆⁰, only four K subbands of which have been observed. For both isotopic species, a standard deviation of about 0.002 cm^?1 has been obtained for about 750 lines of ν₂ + ν₃ and 2ν₆⁰.     

Extended assignment and analysis of the ν2 and ν4 infrared bands of 12CH4

Infrared spectra of the ν₂ and ν₄ bands of ¹²CH₄ have been assigned up to J′ = 20 in the ν₄ band and J′ = 17 in the ν₂ band. Assignments are presented for over 1000 transitions ranging from 1123 to 1712 cm^?1, which involve 652 upper-state energy levels of the two bands. The 652 upper-state levels have been fitted with a weighted standard deviation of 0.0026 cm^?1, almost all levels being reproduced to within their experimental error, by a Hamiltonian for the coupled upper states containing 28 refining parameters and 4 fixed parameters. Calculated relative intensities are also tabulated and discussed in relation to recent experimental intensity measurements.     

The ν5 and ν3 Raman bands of CH2D2

The ν₅ and ν₃ Raman bands of CH₂D₂ have been recorded with a resolution of 0.35 cm^?1. The ν₃ state is well known from infrared studies. Three hundred twenty-nine transitions of the ν₅ band were analyzed, assuming an unperturbed upper state, giving a standard deviation on the fit of the upper-state energies of 0.037 cm^?1, The constants A, B, C, Δ_J, Δ_JK, and Δ_K differed significantly from the ground-state values, and ν₅ was determined as 1331.41 ± 0.05 cm^?1. This work represents the first complete analysis of the fine structure of a rotation-vibrational Raman band for an asymmetric rotor. The ν₅ state could not be analyzed in infrared so this investigation, once more, demonstrates the usefulness of the Raman method.     

High-resolution infrared spectrum and analysis of the ν1 band of CF337Cl

The rotational structure of CF₃³⁷Cl ν₁ band has been investigated using spectra of trifluorochloromethane in natural isotopic abundance, recorded with a tunable diode laser spectrometer. The spectra analyzed have been obtained by keeping the sample at low temperature (～200 K) to minimize the strong interference arising from “hot” band transitions. The K structure of many P(J) and R(J) multiplets has been resolved and positively identified: the maximum J value reached in the P and R branches was 38 and 40, respectively. About 650 unblended lines have been used for the least-squares fit to the energy expression including the quartic centrifugal distortion coefficients. Molecular constants for the ν₁ band of CF₃³⁷Cl have been derived. A weak perturbation affecting the rotational levels with K = 18 and J′ ≥ 36 has also been observed.     

High-resolution infrared atmospheric spectra of ozone in the 10-μm region: Analysis of ν1 and ν3 bands-assignment of the (ν1 + ν2) − ν2 band

1988 lines of ozone have been observed in the atmospheric spectrum in the region 1060 to 1220 cm^?1, 1394 of them have been assigned to the ν₁ band, and 480 to the ν₃, particularly corresponding to ΔK_?1 = 2. The analysis has been performed using the Watson Hamiltonian, taking account of the strong Coriolis coupling between the 001 and 100 levels. The constants for the latter two states, the spectra and a listing of the observed and calculated wave-numbers, with their assignment, are given. In addition, 114 lines of the “hot” band (ν₁ + ν₂) ? ν₂ have been observed and assigned and are reported.     

Complement to the analysis of the ν5 band of 12CD3H

A new analysis of the ν₅ band of ¹²CD₃H is presented using the ground state constants that were determined from the three fundamentals ν₃, ν₅, and ν₆. New lines are assigned and the fit based on 1169 observed transitions including J′ and K′ values up to 23 leads to a set of 16 spectroscopic constants for v₅ = 1, allowing the reproduction of experimental wavenumbers with a standard deviation of 0.0047 cm^?1.     

Analysis of the ν2 and ν4 infrared bands of CD4

The infrared spectrum of totally deuterated methane CD₄ has been recorded between 930 cm^?1 and 1180 cm^?1 under high resolution (0.003 cm^?1). The ν₂ and ν₄ bands of ¹²CD₄ have been reanalyzed on the basis of a complete third-order Hamiltonian including all the coupling terms linking the upper states of the two bands. A set of only 16 self-consistent parameters have been adjusted to fit more than 1650 assigned transitions reaching a maximum upper state J value of 20. The obtained standard deviation is 0.0041 cm^?1. In addition, 171 lines of the ν₄ band of ¹³CD₄ have been assigned. They have been analyzed, in the same dyad scheme, by adjusting 7 parameters of the ν₄ band together with the main ζ₂₄ Coriolis parameter. The obtained standard deviation is only 0.0012 cm^?1.     

Vibrational spectra and force constants of symmetric tops: ν1, ν5, and 2ν5 of CF335Cl and CF337Cl

The gas phase infrared spectra of CF₃³⁵Cl and CF₃³⁷Cl have been recorded in the ν₁ region and 2ν₅ regions with a resolution of 0.09 cm^?1. Additionally the ν₅ fundamental of CF₃Cl, with natural isotopic abundance, has been reinvestigated with a resolution of approximately 0.36 cm^?1. Molecular constants have been evaluated from the observed spectra by means of polynomials and band contour simulation. The possibility of a Fermi resonance between ν₁ and 2ν₅ is discussed.     

Extensive high-resolution study of the crowded rovibrational CH3F spectrum around 3000 cm−1

The infrared spectrum of CH₃F has been remeasured from 2800 to 3160 cm^?1 with a Fourier spectrometer at a resolution of 0.005 cm^?1. By a systematic use of ground-state combination differences, we have assigned 5200 transitions, including several hundred “forbidden” transitions. They can be distributed into seven vibrational bands, which are mixtures of ν₄, ν₁, 2ν₅², 2ν₅⁰, ν₂ + ν₅, 2ν₂, and 3ν₃. More than 20 local resonances have been detected as well as 11 subbands with A₁A₂ splittings. We have attempted to fit all these data in a global model of the “limited-matrix” type including the 6 × 6 resonance due to ζ₂₅^ν, two Fermitype resonances linking ν₁ with 2ν₅⁰ and 2ν₂, respectively, a Coriolis resonance between ν₄ and 2ν₅², and other minor interactions. We conclude that the use of an “infinite-chain” program is unavoidable. We have also identified 80 transitions as belonging to the ν₄ band of ¹³CH₃F occurring in natural abundance.     

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.