High-Resolution Double Velocity Map Imaging Photoelectron Photoion Coincidence Spectrometer for Gas-Phase Reaction Kinetics

We present a new photoelectron photoion co-incidence (PEPICO) spectrometer that combines high mass resolution of cations with independently adjustable velocity map imaging of both cations and electrons. We photoionize atoms and molecules using fixed-frequency vacuum ultraviolet radiation. Mass-resolved photoelectron spectra associated with each cation's mass-to-charge ratio can be obtained by inversion of the photoelectron image. The mass-resolved photoelectron spectra enable kinetic time-resolved probing of chemical reactions with isomeric resolution using fixed-frequency radiation sources amenable to small laboratory settings. The instrument accom-modates a variety of sample delivery sources to explore a broad range of physical chemistry. To demonstrate the time-resolved capabilities of the instrument, we study the 193 nm photodissociation of SO2 via the (C) over tilde(B-1(2)) <- (X) over tilde((1)A(1)) transition. In addition to the well-documented O(P-3(j)) + SO((3)Sigma(-)) channel, we observe direct evidence for a small yield of S(P-3(j)) + O-2((3)Sigma(-)(g)) as a primary photodissociation product channel, which may impact sulfur mass-independent fractionation chemistry.