Interpretation of Raman spectra of van der Waals dimers in argon

摘要

The rotational and vibrational eigenenergies of all bound and predissociating states of theSgr;gplus;Ar2dimer are computed, together with certain averages of the nuclear wavefunctions needed for the computation of the Raman intensities for each transition. The MSV III potential of Parson, Siska, and Lee is used. With this information the complete rotational and vibrationhyphen;rotation Raman spectra of the argon vanhyphen;derhyphen;Waals molecule is obtained and found to consist of truncated and superimposed line sequences. They are thus characteristically different from such spectra of ordinary molecules. A theoretical ``lowhyphen;resolution'' spectrum is obtained by superposition of approximated instrumental profiles for each line in the spectrum. At the lowest temperature (103deg;K) of the experiment nearly all of the observed intensity distribution is due to the dimer Ar2. At high temperatures (300deg;K) the experimental spectrum is due largely to the scattering of light by pairs of atoms in flyhyphen;by collisions, not to molecules. The Raman intensity maxima at plusmn;8.3 cmminus;1shift, therefore, must be explained in terms of the former. The apparent insignificance of the rotationhyphen;vibration Raman bands in comparison to the pure rotational bands can be explained by adoption of a simple model for the anisotropy of the polarizability tensor.