Formation and photodissociation of M + –C 6 H 6 (M + = V + and Ta + ) and Ta + –C 6 H 4 complexes in a time‐of‐flight mass spectrometer

A series of cyclic hydrocarbons were introduced to react with V + and Ta + using a pulsed beam expansion source in a time‐of‐flight mass spectrometer. The third‐row metal Ta + displayed high reactivity in dehydrogenation to form benzyne complexes, whereas benzene complexes were the terminal products for V + . M + –C 6 H 6 (M + = V + and Ta + ) and Ta + –C 6 H 4 were selected to perform the photodissociation experiments. In contrast to the V + fragment formation via simple cleavage of the V + –C 6 H 6 bond, a photoinduced loss of C 2 H 2 occurred in both the Ta + –C 6 H 6 and Ta + –C 6 H 4 complexes. Plausible explanations involved in the formation of Ta + –C 6 H 6 and Ta + –C 6 H 4 complexes are given for observing such photo‐induced dissociation. The observed photodissociation in Ta + –C 6 H 6 is analogous to the dissociative process previously investigated in metal ion–molecule reactions. The photodissociation spectrum of Ta + –C 6 H 4 was obtained by recording the appearance of Ta + –C 4 H 2 as a function of wavelength and yielded a dissociation energy of 91 ± 1 kcal mol −1 . Copyright © 2001 John Wiley & Sons, Ltd.