The variation of translational energy release in collision-induced dissociations of polyatomic ions with initial kinetic energy and with observation angle. I. Theoretical considerations

Abstract

Angle-resolved mass spectrometry has hitherto focused upon variations in relative yields of fragment ions formed in collision-induced dissociations. This paper investigates the sequence of assumptions which must be made in order to interpret observed variations in peak widths, as the observation angle is varied, in terms of energy deposited in the projectile ion by the collision. Some of these assumptions, such as the nature of the collisional excitation mechanism, and the relationship of the energy thus deposited to the total internal energy of those ions sampled by the fragmentation process, are common to both types of experiment. Other assumptions, such as the manner in which the total internal energy of the reacting ion is partitioned into translational energy of the fragments, are peculiar to the peak width measurements. The latter, however, are free from ambiguities of interpretation arising from convolution of the collisional scattering with differences in angular distributions of fragment ions arising only from differences in translational energy release. For both types of experiment the situation is complex, and interpretation requires considerable care.