Unimolecular neutral and ion kinetics by variable‐time neutralization—reionization mass spectrometry

A new method is described for the determination of rate parameters of unimolecular dissociations of neutral intermediates and ions produced by collisional neutralization and reionization at kiloelectronvolt kinetic energies. The method utilizes variable time‐scales for neutral and ion dissociations to obtain time‐dependent survivor and product ion yields. Kinetic analysis then provides phenomenological rate constants for both neutral and ion dissociations. Neutralization with CH3I, NO, (C2H5)2O, C6H6 and Xe of methyl iodide cation radicals is shown to produce the intermediate neutral molecules with different internal energies, resulting in different rates of neutral and ion dissociations. Vibrational excitation in neutralized CH3I results in neutral dissociations with rate parameters in the (1–3) × 105 s–1 range. The origin of neutral excitation by fast collision is explained by the intermediate formation of highly excited Rydberg states that decay by photon emission to the vibrationally excited ground state of the molecule.