Third-order theory of the line intensities in the allowed and forbidden vibrational-rotational bands of C 3 v molecules

• Published in: Journal of molecular spectroscopy Vol. 124; no. 2; pp. 285 - 305
• Main Authors: Aliev, M.R., Papoušek, D., Urban, Š.
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 1987
• ISSN: 0022-2852; 1096-083X
• DOI: 10.1016/0022-2852(87)90142-1

A third-order theory of the intensities of the allowed and “forbidden” (perturbation-allowed) transitions to the fundamental vibrational levels of C 3 v semirigid molecules has been worked out by using the method of contact transformations applied to the electric dipole moment operator. Explicit expressions have been obtained for the linestrengths of the allowed (Δ k = 0, ±1) as well as forbidden (Δ k = ±2, ±3, ±4) transitions from the ground vibronic state to the fundamental vibrational levels of C 3 v molecules. The treatment takes into account all the important Coriolis and anharmonic interactions in a C 3 v molecule, including the effect of the “2, 2” and “2, −1” l-type interactions and the Δ k = ±3 interactions on the intensities of the allowed and forbidden vibrational-rotational transitions. The expressions for the linestrengths of the allowed and forbidden transitions are given here in a form suitable to fit the experimental data on the intensities in the vibrational-rotational spectra of C 3 v molecules.