S. Klee

Simultaneous Rovibrational Analysis of the ν2, ν3, ν5, and ν6 Bands of H312CF

Abstract A total of 4892 transition wavenumbers of the ν 2 , ν 3 , ν 5 , and ν 6 fundamental bands of H 3 12 CF and 1469 frequencies of the rotational transitions in the v 2 = 1, v 3 = 1, v 5 = 1, and v 6 = 1 vibrational states have been fitted simultaneously by taking explicitly into account various Coriolis interactions, l -type interactions, and α-resonance terms between and within the vibrational states. The standard deviation of the fit using 71 parameters was 8.10 × 10 −5 cm −1 for the infrared data and 0.198 MHz for the rotational data. This study clearly shows that in order to obtain a really quantitative fit of the highly precise data of vibration–rotational and rotational spectroscopy, it is necessary to fit all the data simultaneously using a variational approach. The deperturbed values of the upper state rotational constants differ significantly from those obtained previously in fitting the ν 3 and ν 6 bands as isolated bands and the ν 2 /ν 5 bands by a variational approach. This is important for the precise determination of the equilibrium structure of methyl fluoride (J. Demaison, J. Breidung, W. Thiel, and D. Papousek, Struct. Chem., in press). Besides this, the results can be used in further studies of the reduced Hamiltonians for more complicated systems of interacting vibrational levels.

The fundamental vibration—rotational band of gaseous DCl in absorption at 297 K and at 12 K

Abstract Infrared spectra of gaseous deuterium chloride have been measured with an interferometric spectrometer in the region of the fundamental vibration—rotational band with resolution 0.23 m−1. For these measurements the conditions were either a static sample of DCl in a conventional cell of length 0.27 m at 297 K or DCl in admixture with CO and argon flowing through a slit nozzle into an evacuated chamber. By means of adiabatic expansion the latter conditions produced a supersonic jet, in which the effective rotational temperature of both DCl and CO at the region of the measurements was (12 ± 1.5) K. The relative precision 0.004 m−1 and absolute accuracy 0.04 m−1 of the measurements of the bands of 2H35Cl and 2H37Cl of the static gas make the lines suitable as secondary standards for calibration of the scale of spectrometers in the range of wavenumber 189,000 ν m−1

Assignment of coherent anti-stokes Raman spectra of the ν1 bands of ammonia: 14ND3 and 15ND3

Abstract High-resolution FTIR spectra of the ν 1 bands of both 14 ND 3 and 15 ND 3 species were recorded with the Bruker spectrometer in Giessen. The spectra were assigned using the interactive program combining the Loomis-Wood technique with ground state combination difference checks. New sets of molecular constants of the ν 1 vibrational levels of both isotopomers are presented. The ν 1 rovibrational energies derived from the frequencies of the assigned transitions have made possible calculations of the Raman transition frequencies required for a simulation of the Coherent Anti-Stokes Raman Scattering (CARS) spectra. A satisfactory agreement of the simulated CARS spectra with the experimental ones was achieved.

Far-infrared spectrum of 13CH3F between 23 and 84 cm−1

Abstract The Fourier transform spectrum of the pure rotational transitions in the ground vibrational state of 13CH3F was measured at an unapodized resolution 0.0019 cm−1 in the 23–84 cm−1 spectrum region at elevated temperature 360 K. 527 lines with J ≤ 50 have been assigned and fitted simultaneously with the previously measured microwave and submillimeter-wave rotational transitions, and combination differences generated from the ν3 band [Papousek, Tesař, Pracna, Kauppinen, Belov, and Tretyakov, J. Mol. Spectrosc., 146, 127–134 (1991)]. Improved set of spectroscopic parameters was obtained for the ground state of 13CH3F except for the sextic coefficient HJ0, which is not determinable even from data with J ≤ 50.

Far-infrared spectroscopy of CH3OD in highly excited torsional states and the atlas of the Fourier transform spectra in the range 200-350 cm(-1).

The high resolution Fourier transform far-infrared (FIR) spectrum of the torsion rotation band of CH3OD has been analyzed for the highly excited torsion states (n > or = 2) in the vibrational ground state. The spectrum shows splitting of the lines due to strong torsional-rotational-vibrational interactions in the molecule. Assignments were possible for rotational sub-bands in the torsional state as high as n = 4 and for K values up to 8 and J values of up to approximately 30 in most cases, for all the symmetry species. For the third excited torsional state n = 3 assignments were possible to K = 10. The data were analyzed with the help of the energy expansion model, which has been proven very successful in methanol. The state dependent expansion parameters are presented. These molecular parameters were able to reproduce the observed wavenumbers almost to within experimental accuracy of 0.0002 cm(-1) for clean unblended lines. These expansion coefficients should prove valuable in the calculation of precise energy values for excited torsional states up to n = 4, which is way above the torsional barrier. The detailed high-resolution spectral atlas of CH3OD has been presented in the range 200-350 cm(-1). This atlas is an extension of our earlier atlas in the range 20-205 cm(-1). The availability of this atlas in the journal will be very valuable for spectroscopists and astrophysicists seeking information in the infrared (IR) region in the laboratory and in outer space.

A Partial Structure of the Anti Rotamer of 1,2-Difluoroethane from the Analysis of a Band in the High-Resolution Infrared Spectrum

Two regions in the infrared spectrum of gaseous 1,2-difluoroethane at room temperature have been investigated at high resolution. Although bands due to the abundant gauche rotamer dominate the spectrum, a C-type band centered at 3001.89 cm-1 and a largely B-type band centered at 284.260 cm-1 have been shown to be due to the anti rotamer. From its rotational structure the C-type band is confirmed as being due to ν7, the antisymmetric CH2 stretching mode of au symmetry. The B-type band is due to ν18, which is largely the antisymmetric CF bending mode of bu symmetry. The rotational structure of the B-type band, recorded with exceptional resolution in a difficult spectral region, has been analyzed in detail. From the assignment of over 2000 lines, rotational constants have been fitted to the ground state and the upper state. The ground state constants are 1.057 385 7 (11), 0.129 390 34 (26), and 0.120 654 86 (19) cm-1 for this near-prolate symmetric top (κ = −0.9813). These rotational constants imply an incre...

High-resolution Fourier-transform infrared spectrum of the13CH3F fundamental band of13CH3F

Thev6 vibration-rotational band of13CH3F has been measured in the range 1070–1260 cm−1 using a Fourier-transform spectrometer with unapodized resolution 0.0027 cm−1. The wavenumbers of 1262 vibration-rotational transitions to thev6=1 (E) vibrational state have been assigned and fitted by least squares with the standard deviation of the fit 1.31×10−4 cm−1. This made it possible to determine 19 spectroscopical parameters of thev6=1 state including parameters of the Δk=±2, Δl=∓2 and Δk=±4, Δl=∓2 interactions leading to theA1−A2 splittings of many rotational levels withkl=+1 andkl=−2.