On the method and results of calculation of vibrational tetrahedral sub-level energies and resonance interactions in vibrational spectra of high symmetry molecules: CH4 and GeH4 as an application of the XY4 (Td) molecule.

We report here the analytical description of one of the important problems in the study of XY4 (Td) molecules, namely, description of vibrational tetrahedral sub-level structures and resonance interactions caused by the high symmetry of a molecule. The results obtained are applied to description of the vibrational energy spectrum of the CH4 and GeH4 molecules.

High-resolution spectroscopy of C2H3D: Line positions and energy structure of the strongly interacting ν10,ν7,ν8,ν4 and ν6 bands.

High resolution infrared spectra of C2H3D were recorded in the region of 550-1950 cm-1 with a Bruker IFS125 HR Fourier transform infrared spectrometers and rotational structures of the five lowest strongly interacting ν10, ν7,ν8,ν4 and ν6 bands were analyzed. The number of about 28000 transitions (4200/6800/5600/5000/6400 for the bands ν10,ν7,ν8,ν4 and ν6) with Jmax = 40 and Kamax = 20 were assigned to these five bands. The weighted fit of 3990 upper energy values obtained from the experimentally recorded transitions was made with a Hamiltonian which takes into account resonance interactions between all studied bands as well as with the sixth ν3 band which was considered in this case as a "dark" one. As the result of analysis, a set of 279 fitted parameters was obtained which reproduces the initial 3990 upper "experimental" ro-vibrational energy values with the drms=1.7×10-4 cm-1; the initial nonsaturated, unblended and not very weak of 28000 assigned transitions are reproduced with the drms=2.2×10-4 cm-1. Ground state parameters of the C2H3D molecule were improved as well.

High resolution spectroscopy of the ν1+ν3 band of the 35ClO2 free radical: Spin-rotation-vibration interactions.

The high resolution spectrum of the ν1+ν3 band of the 35ClO2 free radical was recorded with a Bruker IFS 125HR Fourier transform infrared spectrometer and theoretically analysed with an improved theoretical basis including the reduced effective spin-rotation Hamiltonian (which takes into account sixth order operators describing spin-rotational interactions) and a newly created computer code ROVDES for the ro-vibrational spectra of open-shell free radicals. About 2600 spin-ro-vibrational transitions with the values Nmax=59 and Kamax=17 (being about 2.4 times higher in comparison with the number of assigned transitions known in the literature) were assigned to the ν1+ν3 band of 35ClO2 and 1049 spin-ro-vibrational energies (produced only from unblended non-saturated and not very weak experimental lines) of the (101) upper vibrational state were obtained. A set of 30 varied parameters of the effective spin-rotation-vibration Hamiltonian of the (101) vibrational state (vibrational energy, 17 rotational and centrifugal distortion parameters and 12 are spin-rotational ones) was determined from the weighted fit of parameters of the effective spin-rotational Hamiltonian in A-reduction and Ir-representation. The obtained set of parameters reproduces the initial 1049 "experimental" upper state energies with the drms=2.5×10-4 cm-1 which is close to the experimental uncertainty of the recorded spectra and is almost 70 times higher in comparison with the analogous reproduction of the same initial upper energies with the use of parameters from (J.Mol.Spectrosc.,158,347-356(1993)).

High resolution FTIR spectroscopy of germane: First study of 76GeH4 in the region of Tetrad of the strongly interacting ν1+ν2,ν1+ν4,ν2+ν3 and ν3+ν4 ro-vibrational bands.

The infrared spectra of germane, purified and enriched up to 88.1% of 76GeH4, was measured at the temperature of (22.6±0.1) °C and different pressures with a Bruker Fourier transform infrared spectrometer IFS125HR and analyzed for the first time in the region of 2700-3200 cm-1 where the stretching-bending Tetrad (ν1+ν2,ν1+ν4, ν2+ν3 and ν3+ν4 bands) of the ro-vibrational Octad of germane is located. The 3595 transitions belonging to the eight sub-bands of the Tetrad were assigned and theoretically analysed in the frame of the effective Hamiltonian model. The obtained set of 106 fitted parameters reproduces the initial 3595 experimental line positions with the drms=6.81×10-4 cm-1. The presence of numerous resonance interactions in the Tetrad is discussed.

Survey of the high resolution infrared spectrum of methane ((12)CH4 and (13)CH4): partial vibrational assignment extended towards 12,000 cm(-1.).

We have recorded the complete infrared spectrum of methane (12)CH4 and its second most abundant isotopomer (13)CH4 extending from the fundamental range starting at 1000 cm(-1) up to the overtone region near 12,000 cm(-1) in the near infrared at the limit towards the visible range, at temperatures of about 80 K and also at 298 K with Doppler limited resolution in the gas phase by means of interferometric Fourier transform spectroscopy using the Bruker IFS 125 HR prototype (ZP 2001) of the ETH Zürich laboratory. This provides the so far most complete data set on methane spectra in this range at high resolution. In the present work we report in particular those results, where the partial rovibrational analysis allows for the direct assignment of pure (J = 0) vibrational levels including high excitation. These results substantially extend the accurate knowledge of vibrational band centers to higher energies and provide a benchmark for both the comparison with theoretical results on the one hand and atmospheric spectroscopy on the other hand. We also present a simple effective Hamiltonian analysis, which is discussed in terms of vibrational level assignments and (13)C isotope effects.

High-resolution near infrared spectroscopy and vibrational dynamics of dideuteromethane (CH2D2).

We report the infrared spectrum of CH(2)D(2) measured in the range from 2800 to 6600 cm(-1) with the Zurich high-resolution Fourier transform interferometer Bruker IFS 125 prototype (ZP 2001, with instrumental bandwidth less than 10(-3) cm(-1)) at 78 K in a collisional enclosive flow cooling cell used in the static mode. Precise experimental values (with uncertainties between 0.0001 and 0.001 cm(-1)) were obtained for the band centers by specific assignment of transitions to the J = 0 level of 71 vibrational levels. In combination with 22 previously known band centers, these new results were used as the initial information for the determination of the harmonic frequencies, force constant parameters F(ij), anharmonic coefficients, and vibrational resonance interaction parameters. A set of 47 fitted parameters for an effective Hamiltonian reproduces the vibrational level structure of the CH(2)D(2) molecule up to 6600 cm(-1) with a root-mean-square deviation d(rms) = 0.67 cm(-1). The results are discussed in relation to the multidimensional potential hypersurface of methane and its vibrational dynamics.

High resolution Fourier transform spectroscopy of CH2D2 in the region 2350-2650 cm(-1): the bands nu5 + nu7, 2nu9, nu3 + nu4, nu3 + nu7 and nu5 + nu9.

The IR spectrum of the CH2D2 molecule has been measured in the region of 2350-2650 cm(-1) on a Bomem DA002 Fourier transform spectrometer with a resolution of 0.004 cm(-1) (FWHM, apodized) and analyzed with a Hamiltonian model which takes into account resonance interactions between all vibrational states in that region. More than 3000 transitions have been assigned to the bands 2nu9, nu3 + nu4, nu5 + nu9, nu5 + nu7 and nu3 + nu7 using ground state combination differences from the known ground state parameters. A set of 115 spectroscopic parameters for the excited vibrational states is obtained from a least squares adjustment. This reproduces the 646 initial upper ro-vibrational energies used in the fit with a d(rms) = 0.0036 cm(-1).