The CI calculation of the frequency-dependent polarizability and some optical properties for N₂ and O₂

Abstract

The frequency-dependent polarizability tensor of N₂ and O₂ was calculated as a function of internuclear distance using the recently-developed frequency-dependent moment method. The method enables us to calculate the polarizability tensor directly from the large CI hamiltonian matrix, without the explicit knowledge of the eigenvectors of the matrix. The frequency-dependent moment was divided into the ‘discrete’ and ‘continuum’ part. The ‘discrete’ part of the frequency-dependent polarizability was evaluated from the eigenvalues and eigenvectors of the low-lying excited states, while the ‘continuum’ part was calculated by solving a simultaneous linear equation. In this way, the frequency-dependent polarizability tensor could be evaluated even near the resonances. The optical properties such as the refractive index, Raman and Rayleigh scattering cross sections were calculated from the obtained polarizability and its derivative with respect to the bond length, and the results were compared with the experimental data. The potential energy curves for the optically-allowed 1 and 2 ¹Σ⁺ _u and 1 and 2 ¹п _u states of N₂ were also studied.