Near-threshold β-parameter measurements of state-selected rotational transitions to the v+ = 0 level of normal and ortho-D2

Abstract

Photoelectron angular distributions in D2 have been measured for the first time with rotational selectivity. The study focuses on the R(2) 5pπ and R(0) 5pπ Rydberg states, converging on the v+ = 4 vibrational level of the D2+ ion. These Rydberg states autoionize to populate the X2Σg+ (v+ = 0) state of the ion. The angular asymmetry parameter (β) has been determined, across the photon energy region 15.671–15.684 eV, for transitions involving changes in rotational quantum number, between the initial neutral and final ion state, ΔN, of +2 and +4. The β-parameter values obtained for the ΔN = +2 transition indicate that the channel is populated via both p- and f-wave photoemission. The β-parameter value for the R(2) n = 5pπ Rydberg state was found to be closer to zero, particularly for the ΔN = +4 transition. It is suggested that this near-isotropic emission is associated with the photo-excited D2 molecule rotating before the autoionizing decay has had a chance to occur. Measurements have been made in both normal and ortho-D2, confirming the results and verifying that the resonant features originate in even rotational levels of the D2 molecule.