Photodissociation of molecular radical cations of toluenes C7H8+· (I), C6H5CD3+· (II),
C7D8+· (III), cycloheptatriene C7H8+· (IV), and benzene has been studied by the method
of two-pulse two-colour laser photolysis of molecules in a mass spectrometer using
wavelengths 1064, 532, and 355 nm. The I ions formed due to sequential two-photon
ionization of toluene molecules by the 266 nm radiation isomerize supposingly into
5-methylene-cyclohexadiene (VI). Two- and three-photon stepwise dissociation of the I
and II isomers (VI and VI-d3, respectively) induced by the 1064 nm radiation has a
resonance at the third overtone level of CH aliphatic bond stretching vibrations. Internal
energy randomization in the two-photon dissociation is much less for VI-d3 as compared
to VI. The mechanisms of isoenergetic dissociation (two- and one-photon processes
induced by the 1064 and 532 nm radiations, respectively) are different: the one-photon
decay via an electronically excited state proceeds considerably faster than the two-photon
decomposition does in the ground state. The photodissociation cross sections
have been determined. It has been shown that the intensity of CH stretching vibration
overtones can be essentially higher for radical cations than for the neutral molecules.
