Two-site double-core-hole states formed when fast protons capture electrons from aligned N₂

We report on an experimental investigation of 1.04 MeV H + +N 2 electron transfer collisions. The fast protons were stored in the electron-cooler ion-storage ring, CRYRING, and the molecular nitrogen target was provided with a supersonic gas jet. We report momentum distributions of atomic nitrogen dissociation products N q + with charge states q + ( q = 1, 2, 3) which are detected in coincidence with neutralized projectiles. Further, we investigate the influence of the angle between the direction of the incoming projectile beam and the target molecular axis. The orientation of the latter is determined from the momentum vector of one emitted atomic nitrogen fragment ion. We find significantly higher total yields, dominated by N + , of charged atomic dissociation products when the N 2 molecular axis is perpendicular to the incoming H + -beam. The relative contributions from N 2 + - and N 3 + -fragments, however, are strongest when the N 2 axis is aligned—or close to aligned—with the ion beam. This, we suggest, is due to increased probabilities for the formation of two-site double-core-hole states.