Low-energy nondipole effects in molecular nitrogen valence-shell photoionization

Observations are reported for the first time of significant nondipole effects in the photoionization of the outer-valence orbitals of diatomic molecules. Measured nondipole angular-distribution parameters for the 3 sigma(g), 1 pi(u), and 2 sigma(u) shells of N-2 exhibit spectral variations with incident photon energies from thresholds to similar to 200 eV which are attributed via concomitant calculations to particular final-state symmetry waves arising from (E1)circle times(M1,E2) radiation-matter interactions first-order in photon momentum. Comparisons with previously reported K-edge studies in N-2 verify linear scaling with photon momentum, accounting in part for the significantly enhanced nondipole behavior observed in inner-shell ionization at correspondingly higher momentum values in this molecule.