The ultraviolet photodissociation of jet-cooled ClO and BrO radicals

The photodissociation dynamics of jet-cooled ClO and BrO radicals have been studied using resonance-enhanced multiphoton ionization with time-of-flight mass spectrometry. Four asymptotic electronic channels are energetically allowed for ClO photodissociation at 235 nm, although the dominant products observed at 235 nm are Cl(P-2(3/2)) and O(D-1(2)). Polarization-dependent time-of-flight profiles indicate that this channel has an anisotropy parameter of beta=1.2+/-0.2. Evidence for O(P-3(J)) products was detected in coincidence with Cl(P-2(1/2)) fragments, and we estimate that this channel constitutes <3% at this wavelength. In the photodissociation of BrO at 355 nm we observe two asymptotic electronic state channels, Br(P-2(3/2))+O(P-3(2)) and Br(P-2(1/2))+O(P-3(2)) in a 0.75:0.25 ratio. Both channels have an anisotropy parameter of beta=1.5+/-0.1. Based on the measured asymptotic velocities of both channels, we have directly determined the Br-O bond dissociation energy to be 55.8+/-1.0 kcal/mol, providing a heat of formation for the BrO radical at 298 K of 29.7+/-1.0 kcal/mol in good agreement with previous spectroscopic determinations. (C) 2002 American Institute of Physics.