Angular Distributions of Photoelectrons fromH2: Effects of Rotational Autoionization

Fano's theory of photoabsorption by ${\mathrm{H}}_2$ near the ionization threshold is extended to yield photoelectron angular distributions above as well as between the ionization thresholds for alternative rotational states of the ${\mathrm{H}}_2^{+}$ ion. In accordance with recent measurements, the angular distribution of direct photoionization is quite different depending on whether or not the ionization is accompanied by a rotational transition. In the autoionization range between rotational thresholds the angular distribution oscillates along each Rydberg line of the rotational autoionization spectrum, resulting in Beutler-Fano resonance profiles which depend strongly on angle of observation. The results are compared with available experimental data. Angular distributions provide very sensitive tests of the theory. The calculation may serve as a basis for extensions to electronic and vibrational autoionization processes.