On the vibrational state dependence of the asymmetry parameter of angular distribution in the photoelectron spectra

A discussion is given on the changes obtainable in the asymmetry parameter β with vibrational state of the ion in the approximation involving fixed direction of body-frame orientation during the electron ejection. The R dependence of the electronic matrix elements is taken into account by calculation of appropriate displaced oscillator integrals. Inclusion of a nuclear matrix element gives in most cases negligible effect for the direct ionization. β_ν′ are calculated for H₂ and N₂. Expected variations in β_ν′ are compared with recent experimental data on N₂ and CO. Higher partial waves and their effect on β_ν′ are discussed.