Photoelectron Angular Distributions of Rotationally Resolved Autoionizing States of Molecular Nitrogen

Rotationally resolved excitation of N$_2$ just above the ionization threshold allowed the recording of photoelectron angular distributions (PADs) for selected autoionizing levels of the ($X^+\,^2\Sigma^+_g$) $6p\sigma$, $v=2$ and ($X^+\,^2\Sigma^+_g$) $9f$, $v=1$ Rydberg states. Because the direct ionization continuum is weak compared to the autoionizing resonances, the PADs can be predicted using simplified formulae based on the work of Raoult \emph{et al.} [\emph{J. Chim. Phys.} {\bf 77}, 599 (1980)]. The observed PADs are generally in good agreement with these predictions. Photoelectron angular distributions were also recorded for individual rotational levels of the $b' {\,}^1\Sigma_u^+$, $v = 42$ and 43 states, and for two complex resonances arising from the interactions between the $b'$ state and Rydberg states converging to the $X^+$, $A^+$, and $B^+$ states of the ion. The analysis of these PADs is more complex and is still underway.