N4+ photodissociation: Charge exchange of N2+ fragments with Ar

The proportion of N4+ photofragmenting to yield N2+ in X 2Σg+v≳0 states has been measured by observing the yield of the fragments’ charge transfer reaction with Ar. Such a determination is possible because N2+ in the v=0 level has a cross section for charge exchange with Ar that is 2 orders of magnitude smaller than in higher vibrational levels. The fraction of N2+(v≳0) fragments increases from 0.30 at 620 nm to 0.37 at 266 nm. Calculations, which treat the N2+ and N2 fragments as quantum harmonic oscillators and the dissociation coordinate classically, predict an N2+ fragment vibrational content that is of the same order as that observed. The substantial population of vibrationally quiescent N2+ fragments, along with previous kinetic energy release studies of N4+ photodissociation, that show a limited fraction of the available energy appears as translational motion [M. F. Jarrold, A. J. Illies, and M. T. Bowers, J. Chem. Phys. 81, 214 (1984)], suggest that the fate of much of the photon’s energy is either in product rotational motion or in the neutral N2 vibration. Mechanisms for the dissociation are discussed.