Spin-polarized photoelectrons produced by strong-field ionization of randomly aligned nitric oxide

Abstract

We investigate the effect of the molecular alignment of nitric oxide (NO) on nonadiabatic tunnel ionization of degenerate valence orbitals in strong circularly polarized laser fields and on spin polarization of photoelectrons. Our numerical study shows that not only for the alignment parallel to the laser propagation axis [Liu, K.; Barth, I. Phys. Rev. A 2016, 94, 043402] but also for arbitrary alignment angles except for perpendicular alignment, the counter-rotating molecular orbital with respect to the circular polarization of the laser field projected on the plane perpendicular to the molecular axis is ionized more easily. Due to the nonadiabatic effect and the nodal structure of the valence orbitals of NO, the ionization maxima for the and orbitals in right circularly polarized laser fields are obtained for the molecular orientations at the polar angles of around and , respectively. Considering the spin-orbital entanglement in the doubly degenerate electronic ground state of NO, the spin-polarization of photoelectrons is high for parallel alignment, decreases upon increasing the polar angle and vanishes for perpendicular alignment. Averaging over all alignment angles, non-zero spin-polarization of photoelectrons for randomly aligned NO is preserved.