The kinetics of the H-2 (D-2) loss from C2H4+ (C2D4+) ions

The unimolecular H-2/D-2 loss from C2H4+/C2D4+ ions has been investigated i n a threshold photoelectron photoion coincidence spectrometer with electron time of flight discrimination. The experiment shows that the reaction take s place on the microsecond timescale, i.e. is metastable right at the thres hold. The experimental breakdown curve for d(4)-ethene is shifted by 103 me V to a higher excitation energy compared to h(4)-ethene. The entire breakdo wn curves were simulated based on model k(E) curves. Best agreement between experiment and simulation was observed for threshold values of k(E-0) = 7. 0 x 10(5) s(-1) for h(4)-ethene and k(E-0) = 2.5 x 10(4) s(-1) for d(4)-eth ene.