CCSD study of anharmonic Raman cross sections of fundamental, overtone, and combination transitions

Abstract

AbstractA methodology is presented for the study of fundamental, combination, and overtone Raman transitions, including a treatment based on the contact transformation theory for the mechanical anharmonicity from the cubic potential energy terms. The results obtained for acetylene and its deutered isotopologues show that anharmonicity effects on the Raman intensities can be very strong, particularly in the second‐order transitions. On average, these effects vary from 6.4 to 11.6% for fundamental transitions, from 26.8 to 36.0% for combinations, and from 56.3 to 86.6% for the overtones. Quantitative agreement of the calculated fundamental Raman cross sections with experiment was achieved. For combinations, it was determined that only semiquantitative agreement was achieved, while the computed overtone cross sections overestimated the experimental values. © 2012 Wiley Periodicals, Inc.