Speed dependence of collisional relaxation in ground vibrational state of OCS: rotational behaviour.

Accurate experimental data on pressure broadened profiles of (16)O(12)C(32)S pure rotational lines in a broad range of quantum number J have been analyzed taking into account the speed dependence of collisional relaxation. Refined values of collisional self-broadening coefficients are determined and compared to previously known data. New quantitative information on departures of observed line shapes from the traditional Voigt profile is obtained. It is shown that these departures result mainly from the speed dependence of collisional relaxation. Theoretical calculations of self-broadening parameters are performed in the framework of the semiclassical impact Robert-Bonamy formalism where the mean relative molecular speed as well as the Maxwell-Boltzmann distribution of relative speeds is considered. The necessity of allowance for the speed dependence in line shape models is confirmed and satisfactory results have been obtained by arbitrarily limiting the integration of the differential cross section to a finite value of the impact parameter. It is shown for the first time for the whole rotational spectrum that speed dependent models not only improve accuracy of modeling the observed line profiles but also give physically grounded values of collisional relaxation parameters.

Collision cross sections, pressure-broadening coefficients and second virial coefficients for the acetylene-argon complex: experiments and calculations on a new potential energy surface.

Integral cross sections and pressure-broadening coefficients have been measured by molecular beam scattering and by high-resolution infrared spectroscopy, respectively, for the acetylene-argon system. A new potential energy surface (PES) is proposed to describe structure and dynamical properties of this prototypical weakly bound complex. The PES has been parametrized exploiting a novel atom-bond pairwise additive scheme and has been fitted to the experimental data. Calculations of the scattering cross sections (both differential and integral), pressure-broadening, and second virial coefficients have been performed using both the present and also the most recent ab initio PES available in the literature. Analysis of the new experimental data indicates that the anisotropy of the interaction in the well region should be larger than that obtained in ab initio calculations. This is also in line with previous spectroscopic results.

Line frequency shift measurements by diode-laser spectroscopy for CH(3)D-Xe.

The pressure-induced Xe shifting and broadening coefficients for five lines of 12CH(3)D in the nu(3) band near 7.5 microm have been measured using a tunable diode-laser spectrometer. The frequency shift was determined from the simultaneous record of the Xe-broadened line and the same line of pure CH(3)D at low pressure. Comparisons are made with the results of theoretical calculations based on a semiclassical model involving the atom-atom Lennard-Jones (LJ) potential.

Pressure broadening study of carbon disulfide for atmospheric detection.

Preliminary results for collisional broadening are reported for two lines P(8) and R(32) of the nu3-nu1 band of CS2 in mixture with O2 and air. These values and previous results for CS2-N2 enable us to compare the broadening coefficients directly obtained for CS2-air with those derived from CS2-N2 and CS2-O2.

Cyanogen chloride: self-broadening and intensities in the region of 13 microm.

This work presents a synthesis of our results concerning line intensities and self-broadening coefficients for ClCN in the diad (nu1, 2nu 2 0). Absolute band strengths have been determined. The influence of the perturbation in these band strengths due to a Fermi resonance between the 10(0)0 and 02(0)0 levels has been analyzed.

N(2)-Broadening for Methyl Chloride at Low Temperature by Diode-Laser Spectroscopy.

Using a tunable diode-laser spectrometer, we have measured N(2)-broadening coefficients of 87 individual rovibrational lines in the P and R branches of the nu(3) band of methyl chloride (CH(3)(35)Cl) at 203.2 K. These lines with J values ranging from 2 to 22 and K from 0 to 6 are located in the range 711-751 cm(-1). Most of the collisional widths are obtained by modeling the spectral region from the superposition of overlapping Voigt or Rautian profiles. We have reviewed and completed previous measurements of N(2)-broadening coefficients at room temperature in the nu(3) band, in order to compare them to the low-temperature data. A semiclassical calculation, including electrostatic, induction, and dispersion energy contributions, has provided results that are in reasonable agreement with the experimental data at room temperature, but generally larger than the data at low temperature for small or medium J values. The temperature dependence of the collisional broadenings derived from a simple power law has been determined both experimentally and theoretically. Copyright 2001 Academic Press.

Absolute Line Intensities and Self-Broadening Coefficients in the nu(1) Band of (35)Cl(12)C(14)N.

The self-broadening coefficients and the intensities of 29 lines in the nu(1) band of cyanogen chloride ((35)Cl(12)C(14)N) have been measured at high resolution in the range 699-736 cm(-1), using a tunable diode-laser spectrometer. The collisional widths and most of the intensities are obtained by fitting Voigt and Rautian profiles to the measured shapes of the lines. From the analysis of the line intensities we determine the absolute strength as well as the Herman-Wallis factors for the nu(1) band. A semiclassical calculation of the self-broadening coefficients, performed by considering the main electrostatic interactions only, has provided larger results than the experimental data. Copyright 2001 Academic Press.