Observation of rotational predissociation in 20NeH +, 22NeH +, 20NeD +, 40ArH + and D 2+ formed from various precursors

Abstract

Translational energy spectroscopy has been used to investigate the unimolecular dissociation, at keV translational energies, of NeH + → H +, ArH + → H + and D + 2 → D +. For D + 2 in its ground electronic state ( X 2Σ + g), fragmentation is known to proceed solely by the mechanism of rotational predissociation. This study indicates the same mechanism to account for the unimolecular fragmentation of NeH + and possibly for ArH +. For D + 2 five quasibound states have been previously detected using a mass spectrometric technique. In this experiment, D + 2 was formed from a number of deuterated organic molecules, by dissociative electron impact ionization CD 4 was found to produce the largest D + 2 signal, where a total of at least ten and possibly more quasibound states have been identified. The energy releases have been measured for all the observed predissociating states. For D + 2, where theoretical calculations exist, the initial relative populations have been determined and found to lie in a range differing by no more than a factor of four. Populations of rovibronic states were found to depend on the precursor used to form D + 2 and were estimated from the translational energy spectra. For 20NeH +, 22NeH + and 20NeD +, five, three and five predissociating states were observed, respectively, whilst for 40ArH + the very low signal to noise ratio of the H + product allowed only a tentative assignment of the fragmentation mechanism and estimation of a single energy release.