R-matrix calculations of vibrationally resolved electron collisions with molecular hydrogen.

摘要

Electron-H2 is the most basic, fundamental system for the study of electron collisions with molecules and has many interesting features. In particular, at low energy there is a shape resonance associated with the ground state and at higher energy a resonance associated with a dissociative target state. In the region of 10-15 eV there is an enormously complicated resonance structure due to the forest of electronically excited target states present, many of which have associated resonances. Despite a large number of experimental and theoretical studies, many ambiguities remain over the designation, symmetry assignment, parentage and behaviour of different isotopes of these '10 eV' resonances. The purpose of this work is to develop a full description of electron hydrogen molecule collisions at energies up to 14 eV with particular emphasis placed on the troublesome '10 eV' resonances. Ah initio fixed-nuclei scattering calculations have been performed for electron-H2 collisions as a function of H2 bond length using the R-matrix method, up to 2phig total symmetry. The calculations include the seven lowest target states of H2 which are represented by full CI wavefunctions. The time-delay method of fitting has been developed during the course of this work. The use of this method has allowed the tracking of resonance positions and widths, and hence the production of resonance potential curves, where previous methods (most notably the fitting of the eigenphase sum) have failed due to problematic background variation. Several resonances in the 10-14 eV region have been found to be associated with multiple 'parent' target states and in some cases can swap parents as a function of bond length. These phenomena provide an explanation for the inconsistencies in previous assignments of resonances in this region and other anomalies. Vibrational energy levels have been found from the resonance potential curves and compared with experimental studies for H2, D2 and HD. The excellent agreement has allowed the production of a complete theoretical description of all the low-lying resonances. The agreement also provides corroboration of the multiple parent state/parent state swapping phenomena.