Theory of Collision-Induced Line Shapes-Absorption and Light Scattering at Low Density. In: Prigogine I, Rice SA, editors. Advances in Chemical Physics. Hoboken: John Wiley & Sons, Inc.; 1982. pp. 49-112. [DOI: 10.1002/9780470142752.ch2]

Anisotropic and Isotropic Light Scattering Data of Neon Gas Simultaneously Fitted by an Isotropic Ground State Interatomic Potential

The binary anisotropic and isotropic collision-induced light scattering spectra by gaseous room temperature neon, over an extended frequency domain have been used for deriving the empirical multi-parameter Morse–Morse–Morse–Spline van der Waals interatomic potential. These new data of scattering are accurate enough to permit for the first time a reliable determination of the isotropic potential as a function of the interatomic separation. The potential parameters describing the location and depth of the attractive well are given by ε = 41.07 K and r m = 3.087 Å. Comparison with other potentials based on bulk properties and ab initio calculations are presented; the temperature dependence of pressure second virial coefficient, self diffusion, thermal conductivity and viscosity are also discussed for the proposed potentials. In addition, our empirical potential was used to solve the nuclear Schrödinger equation for comparison with and predication of spectroscopic properties of the dimer. The results show that it is the most accurate potential reported to date for this system.

Lineshape and Moment Analysis in Isotropic and Anisotropic Interaction-Induced Light Scattering Spectra of Gaseous Helium

Calibrated Raman spectra of the helium gas diatom at room temperature (294.5 K) have recently been measured over a wide range of intensities, with polarizations of the incident beam parallel and perpendicular to the direction of observation. From the resulting spectra, the isotropic and anisotropic components are separated for the helium diatom. For direct comparison with the measurements, quantum mechanical lineshapes are computed using recent model of the interatomic potential and models of the diatom polarizability tensor invariants as input. New empirical trace and anisotropy parameters, consistent with the spectroscopic measurements, are thus obtained for the helium gas. We compare these where possible with the existing computations based on classical physics, utilizing the first few even moments of the isotropic and anisotropic spectra. Good agreement with ab initio results in the literature is obtained and profiles calculated with these models are in excellent agreement with experiments.

Empirical Models of the Pair-Polarizability Trace and Anisotropy from Polarized and Depolarized Interaction-Induced Light Scattering Spectra for Gaseous Krypton

A method based on classical physics, utilizing the first few even moments of the polarized and depolarized interaction-induced light scattering spectra at room temperature to derive an empirical model for the pair-polarizability trace and anisotropy of interacting atoms, with adjustable free parameters, is described and applied to the spectra of krypton. Good agreement with ab initio and analytical results in the literature is obtained and profiles calculated with our empirical models are in excellent agreement with experiments. Theoretical calculations using these models are compared with the experimental values of the second dielectric constant and second virial Kerr coefficient for this gas. The results show excellent agreement with the experiments.

Classical line shapes based on analytical solutions of bimolecular trajectories in collision induced emission

The classical theory of collision induced emission (CIE) from pairs of dissimilar atoms is studied. This radiation emitted by accelerating dipoles is produced essentially by their overlap and exchange interaction at short range. This classical calculation is based on exact collinear solutions of the trajectories of two spherical particles in a head-on collision under the influence of a Morse potential with a well of arbitrary depth. Without too restrictive conditions a variety of simple solutions in closed form is obtained that illustrates the connection between collision dynamics and CIE. Depending on the well depth and energy of the particles, they may radiate in the far infrared to infrared or visible and shorter wavelength regions. The results are characterized by a fixed total energy. Nevertheless, a connection is demonstrated between the line shape in CIE computed through the trajectory and that based on the emission of a thermally equilibrated system.

Correlation functions in classical gases at high frequency

A general procedure is outlined to determine the exact asymptotic form of spectra in classical gases at high frequency. Examples are the force-force correlation or the velocity autocorrelation function of a tagged particle. For purely repulsive potentials of the form Ar(-n), the asymptotic spectra are proportional to omega(sigma)exp[-(omegatau)(nu)]. Exponent nu and time constant tau depend only on the interparticle potential, while exponent sigma depends in addition on the correlation studied. The analysis makes use of the fact that the high-frequency spectra are dominated by high-energy binary collisions. It is argued that for arbitrary potentials the spectra decay slower than exp(-constxomega(2/3)) and that the results are also relevant for dense fluids. The frequency range is estimated where quantum effects become important.