Molecular dynamics simulations for CO2 spectra. IV. Collisional line-mixing in infrared and Raman bands.

Ab initio calculations of the shapes of pure CO2 infrared and Raman bands under (pressure) conditions for which line-mixing effects are important have been performed using requantized classical molecular dynamics simulations. This approach provides the autocorrelation functions of the dipole vector and isotropic polarizability whose Fourier-Laplace transforms yield the corresponding spectra. For that, the classical equations of dynamics are solved for each molecule among several millions treated as linear rigid rotors and interacting through an anisotropic intermolecular potential. Two of the approximations used in the previous studies have been corrected, allowing the consideration of line-mixing effects without use of any adjusted parameters. The comparisons between calculated and experimental spectra under various conditions of pressure and temperature demonstrate the quality of the theoretical model. This opens promising perspectives for first principle ab initio predictions of line-mixing effects in absorption and scattering spectra of various systems involving linear molecules.

Fermi interaction between the nu1 and the nu2+4 nu(s) bands of Ar...DN2(+).

Two rotationally fully resolved vibrational bands have been assigned unambiguously to the linear deuteron bound Ar...DN(2) (+) complex by using ground state combination differences. The ionic complex is formed in a supersonic planar plasma expansion optimized and controlled by a mass spectrometer and is detected in direct absorption using tunable diode lasers and applying production modulation spectroscopy. The band origins are located at 2436.272 cm(-1) and at 2435.932 cm(-1) and correspond to the nu(1) band (NN stretch) and to the nu(2)+4 nu(s) combination band (DN and intermolecular stretch), respectively. The two bands overlap strongly and the large intensity of the combination band is explained in terms of a Fermi interaction. This interaction perturbs the observed transitions, particularly for low J values. Least-squares fitting yields values for the Fermi interaction parameters of F(0)=0.332 cm(-1) and F(J)=-0.001 46 cm(-1) and results in accurate rotational constants. These are discussed both from an experimental and a theoretical point of view.

Diode-Laser Jet Spectra and Analysis of the nu(1) and nu(4) Fundamentals of CCl(3)F.

High-resolution infrared spectra have been measured for mixtures of CCl(3)F in Ne, expanded in a supersonic planar jet. We present the first analysis for the nu(4) fundamental and a complete analysis for the nu(1) band. Accurate spectroscopic constants have been obtained for both the nu(1) fundamental of the most abundant isotopic species, C(35)Cl(3)F, C(35)Cl(2)(37)ClF, and C(35)Cl(37)Cl(2)F. With respect to an earlier work [M. Snels, A. Beil, H. Hollenstein, M. Quack, U. Schmidt, and F. D'Amato, J. Chem. Phys. 103, 8846-8853 (1995)], the observation of Q branches of the three most abundant isotopomers allowed for an unambiguous determination of the nu(1) band origins. The nu(4) fundamental has not been the subject of a high-resolution analysis up to now. The observation of high-resolution spectra of the central part of the band permitted the determination of band origin, rotational constants, and Coriolis constant for the symmetric-top species, C(35)Cl(3)F. Copyright 2001 Academic Press.

High Resolution IR Study of the Coriolis Coupling between nu3 and nu9 in CH2 35 Cl37 Cl

The infrared spectra of the nu3 and nu9 bands of methylene chloride have been recorded both for isotopically pure CH2 35 Cl2 and for a natural mixture with a resolution of 0.0025-0.004 cm-1 (FWHM) in the range 600-800 cm-1 using a Bruker IFS 120 HR Fourier Transform interferometer. The Coriolis coupling between the two CCl2 stretching fundamentals nu3 and nu9 has been investigated for the CH2 35 Cl37 Cl isotopic species. An effective coupling constant xi39 c = 0.1975(2) cm-1 results from a full rotational analysis of a difference spectrum, obtained by subtracting the CH2 35 Cl2 room temperature spectrum from that of the natural mixture. A least-mean-squares fit of the data to Watson's A-reduction Hamiltonian in the Ir representation yields a set of accurate effective rotational and distortion constants up to quartic terms for the excited states of both fundamental bands. The standard deviation of the fit was 0.893 x 10(-3) cm-1 .