Formation and photodissociation of M+-C6H6 (M+ = V+ and Ta+) and Ta+-C6H4 complexes in a time-of-flight mass spectrometer

A series of cyclic hydrocarbons were introduced to react with V+ and Ta+ us ing a pulsed beam expansion source in a time-of-flight mass spectrometer, T he third-row metal Ta+ displayed high reactivity in dehydrogenation to form benzyne complexes, whereas benzene complexes were the terminal products fo r V+, M+-C6H6 (M+ = V+ and Ta+) and Ta+-C6H4 were selected to perform the p hotodissociation experiments. In contrast to the V+ fragment formation via simple cleavage of the V+-C6H6 bond, a photoinduced loss of C2H2 occurred i n both the Ta+-C6H6 and Ta+-C6H4 complexes. Plausible explanations involved in the formation of Ta+-C6H6 and Ta+-C6H4 complexes are given for observin g such photoinduced dissociation. The observed photodissociation in Ta+-C6H 6 is analogous to the dissociative process previously investigated in metal ion-molecule reactions. The photodissociation spectrum of Ta+-C6H4 was obt ained by recording the appearance of Ta+-C4H2 as a function of wavelength a nd yielded a dissociation energy of 91 +/- 1 kcal mol(-1). Copyright (C) 20 01 John Wiley & Sons, Ltd.