Vibrational intensities. III. Carbon dioxide and nitrous oxide

Abstract

Experimental intensity measurements can be combined with known harmonic and anharmonic potential constants of molecules to determine the variation of dipole moment with displacement. We have used a finite Taylor's series for both potential energy and dipole moment. The effect on intensity of frequency variation over the band is included explicitly for both parallel and perpendicular bands as is Fermi resonance between several bands. Intensities of two fundamental and four combination bands in carbon dioxide were measured. A complete second-order perturbation treatment of intensities was carried out for several bands, and the possible relation of the results to resonance structures is mentioned. The relative importance of electrical and mechanical anharmonicity is indicated. Two cubic potential constants were determined for nitrous oxide from measured intensities, known rotational convergence, normal coordinates, and bond distances. Using these constants a first-order intensity treatment was carried out for several combination bands. The intensities of three fundamental and three combination bands were measured. Discrepancies in measured rotational convergences are mentioned, and possible lines are suggested for further work on nitrous oxide.