Low pressure infrared multiple-photon dissociation dynamics of gaseous ion-molecule complexes

Abstract

The infrared multiple photon dissociation (IRMPD) of gaseous cluster ions has been studied in the ultra-low pressure environment of a Fourier transform ion cyclotron resonance (FTICR) spectrometer. A bottleneck in the IRMPD kinetics of large isolated ions has been observed and tentatively identified as occurring in the upper levels of the vibrational manifold. A previous theory which proposed that IRMPD using low intensity, continuous wave, infrared laser radiation could be treated as a thermal unimolecular reactions has been disproven. Additionally, a new method of tandem mass spectrometry has been developed which uses IRMPD in place of traditional collisional activation to induce the fragmentation of large ions trapped in a FT-ICR spectrometer. The technique of IRMPD/FT-ICR has been combined with the previously developed method of black body radiation induced, thermal unimolecular dissociation to explore the dynamics of chloride-alkyl bromide SN2 reactions. The results of this study provide the first experimental verification of the theoretically predicted mode-specific behaviour of the Cl + CH3Br reaction.