Threshold photoelectron–photoion coincidence mass spectrometric study of ethylene and ethylene-d4

Abstract

Experimental curves have been obtained for the fragmentation of ethylene and ethylene-d4 ions as a function of the internal energy of those ions using threshold photoelectron–photoion coincidence mass spectrometry. The results are compared with the previous results of photoionization mass spectrometry, Hei photoelectron–photoion coicidence, charge exchange experiments, and with quasiequilibrium theory (QET) calculations. The discrepancies between results of these previous experiments and QET calculations do not appear in the present data. It is suggested that ion–molecule reactions competing with charge exchange has led to erroneous conclusions in the interpretation of the charge exchange data. It is concluded that QET does describe the fragmentation of ethylene and ethylene-d4 within the limits of the data and calculations available. The secondary ion fragmentation C2H4+ → C2H3++H → C2H2++2H is discussed in detail with regard to the C2H3+ fragment ion internal energy distribution.