Slow dissociations of thiophenol molecular ion. Study by TRPD and TPIMS (time-resolved, photodissociation and time-resolved photoionization mass spectrometry)

Abstract

Dissociation of thiophenol molecular ion to yield competitive product ions at m/z 84 (C 4 H 4 S + ) and 66 (C 5 H 6 + ) was studied by several techniques. Time-resolved photodissociation at 308 nm (4.20 eV ion internal energy) in the ICR ion trap gave rate constants of 1.3×10 5 s −1 for m/z 84 formation and 8×10 4 s −1 for m/z 66 formation, and at 355 nm (3.66 eV ion internal energy) it gave 2.8×10 3 s −1 for m/z 84 formation, with m/z 66 not observed at this wavelength. Time-resolved photoionization mass spectrometry at 800 μs trapping time gave thresholds of 2.9 eV for m/z 84 formation and 3.2 eV for m/z 66 formation; the photoionization efficiency curves cross at approximately 4 eV internal energy so that m/z 66 si more abundant at energies above this; at 20-μs trapping a kinetic shift of approximately 0.2 eV was observed relative to 800-μs trapping