Rotational Raman intensities and the measured change with internuclear distance of the polarizability anisotropy of H2, D2, N2, O2, and CO

Abstract

The relative intensities of O and S branch lines in the v=1←v=0 Stokes Raman spectrum of gaseous H2, D2, N2, O2, and CO have been measured in order to obtain a parameter χ= (α∥−α⊥)e/{re[∂ (α∥−α⊥)/∂r]e}. Values for χ reflect the detailed molecular electronic structure and are needed in various scattering theories and to correct rotational and vibrational–rotational Raman intensities for molecular nonrigidity and vibrational-rotational interaction. The values of χ obtained are +0.38±0.01 (H2), +0.38±0.01 (D2), +0.45±0.09 (N2), +0.23±0.07 (O2), and +0.27±0.13 (CO). By combining the measured values of χ with experimental values for 〈α∥−α⊥〉v=0 in the literature, the following values of the polarizability anisotropy and its first derivative at re are obtained: (α∥−α⊥)e=0.288 (H2), 0.282 (D2), 0.691 (N2), 1.080 (O2), and 0.525 (CO) Å3; [∂ (α∥−α⊥)/∂r]e=1.02 (H2), 1.00 (D2), 1.40 (N2) 3.89 (O2), and 1.72 (CO) Å2. These values are compared with literature theoretical values. Molecular polarizability is an experimentally accessible quantity which reflects in a rather direct way the electronic structure of simple molecules. For this reason the orientational anisotropy of molecular polarizability and its variation with internuclear distance are of fundamental interest in developing understanding of the detailed electronic structure of diatomic molecules. Polarizability anistropies and their derivatives are directly related to both absolute and relative intensities of vibrational and rotational Raman transitions.