Comparison of low-energy collisionally induced dissociation of n-butyl benzene ions with photodissociation

Abstract

The collisionally induced dissociation of n-butyl benzene ions to form C 7H 7 + or C 7H 8 + fragments has been examined at centre-of-mass collision energies in the range 0–30 eV using a triple quadrupole. The target gases were methane, nitrogen, argon, propane and krypton. The ratio of the intensities of the fragment ions has previously been shown by photodissociation experiments to be a very sensitive function of the internal excitation energy of the parent ion. For all the target gases, the ratio of C 7H 7 + to C 7H 8 + rose almost linearly with centre-of-mass collision energy above the threshold for C 7H 7 + formation, but the ratio reached a maximum at an energy of ∼ 9 eV and slowly declined at higher energies. The maximum ratio was target-dependent and a comparison with the photodissociation data suggests that slightly lower amounts of excitation energy are available when the target is polyatomic. The equivalent internal excitation energies are much higher than those found in high-energy collisional activation, indicating the efficiency of the direct translational to vibrational energy conversion that occurs at low collision energies. Measurements of fragmention energy distributions show distinct differences between C 7H 7 + and C 7H 8 +