Absolute cross sections for collision-induced scattering of light by binary pairs of argon atoms

Abstract

Absolute intensities of the collision-induced Raman spectrum of argon are measured relative to certain rotational Raman lines of known intensity in hydrogen and nitrogen. Using the 4880 Å laser line for excitation and a detector sensitive to both polarizations, at a frequency shift of -12 wavenumbers, the cross section times unit volume and per unit wavenumber band, for scattering of light at right angles by binary pairs of argon atoms, is found to be 2·89 × 10^-53 cm⁶±7 per cent. Rigorous wave-mechanical computations on the basis of Placzek's polarizability theory predict a value of 2·83 × 10^-53 cm⁶±2 per cent and reproduce the experimental spectrum from about 6 to 60 wavenumbers, if the empirical MSV III potential is used together with the point-dipole model of the anisotropy of the polarizability tensor of two interacting atoms. For comparison, computations based on the rigorous classical trajectories of the collisions are presented. If the same potential function and model of the anisotropy are employed for frequency shifts larger than 10 wavenumbers, the classical treatment agrees with both experiment and wave-mechanical theory.