A THEORETICAL-STUDY OF C-3 MOLECULE TRAPPED IN RARE-GAS MATRICES - INFLUENCE OF BENT OR LINEAR CONFIGURATION ON THE INFRARED-SPECTRA

In the infrared spectra of C-3 trapped in rare gas matrices at low tem peratures T similar or equal to 10 K, two bands in the nu(3) asymmetri c stretching region have been observed, one intense at higher frequenc y (HF) and the other, weaker at lower frequency (LF), These bands have been attributed to two different trapping sites in the matrix. In thi s paper semi-empirical atom-atom potential energy calculations, based on pairwise additive interactions, have been performed in order to und erstand the nature of these trapping sites and the influence of the ma trix on the C-3 molecular geometry. The vibrational frequency shifts d ue to the matrix surroundings are calculated for bent and linear molec ular configurations in several different trapping sites. In the calcul ated infrared spectra, no significant absorption occurs in the nu(1) s ymmetric stretching region, while the nu(2) bending and nu(3) asymmetr ic stretching modes exhibit weak and strong bands, respectively. Final ly, from a comparison of the calculated and experimental spectra in th e nu(3) region, it is predicted that C-3 should be in the bent configu ration when trapped in a matrix, as observed. (C) 1997 Elsevier Scienc e B.V.