Unimolecular Photochemistry Studied by Photodissociation-Photoionization Mass Spectrometry

Photochemical reactions are commonly studied in the condensed phase or in a high pressure gas. The primary photodissociation products are inferred from distributions of stable compounds produced by secondary reactions. As these investigations are extended to molecules of increasing size and complexity, identification of the primary products becomes difficult owing to the large number of possible secondary reactions. In photodissociation-photoionization mass spectrometry (PDPI-MS), molecular photodissociation is performed at low pressure in the source region of a mass spectrometer. After a short time delay, the neutral photodissociation products are softly ionized with coherent vacuum ultraviolet radiation and mass analyzed. Unlike photochemical experiments at high pressure, PDPI permits direct observation of the entire product distribution on the microsecond timescale.