The effects of nuclear motion in the photoelectron spectra of diatomic molecules

Different methods for the computation of rovibronic cross sections and angular distributions of photoelectrons have been evaluated for the photoionization of diatomic molecules.

The methods considered were: (i) the Franck-Condon approximation, (ii) the r-centroid approximation, and, (iii) explicit integration over the nuclear coordinates.

In each of the methods, the effect of the rotational motion on the vibrational wave functions could be taken into account. The effects of vibration-rotation interaction were noticeable for H₂, HD, and D₂, but negligible for N₂ and CO.

The rotational structures of the vibronic bands in a vibronic progression are similar, unless a shape resonance is present.

The r-centroid method represents an improvement over the Franck-Condon approximation, in the absence of shape resonances. If a shape resonance is present, the Franck-Condon and the r-centroid approximations break down; i.e., the r-centroid approximation will no longer represent an improvement over the Franck-Condon approximation.

The SW-Xα model has been used to represent the electronic wave functions involved in the photoionizations.