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).