Near-UV photolysis of substituted phenols, I: 4-fluoro-, 4-chloro-and 4-bromophenol

The experimental techniques of H (Rydberg) atom photofragment translational spectroscopy and resonance-enhanced multiphoton ionisation time-of-flight spectroscopy have been used to investigate the dynamics of H atom loss processes from gas phase 4-fluorophenol (4-FPhOH), 4-chlorophenol (4-ClPhOH) and 4-bromophenol (4-BrPhOH) molecules, following excitation at many wavelengths, lambda(phot), in the range between their respective S(1)-S(0) origins (284.768 nm, 287.265 nm and 287.409 nm) and 216 nm. Many of the Total Kinetic Energy Release (TKER) spectra obtained from photolysis of 4-FPhOH show structure, the analysis of which reveals striking parallels with that reported previously for photolysis of bare phenol (M. G. D. Nix, A. L. Devine, B. Cronin, R. N. Dixon and M. N. R. Ashfold, J. Chem. Phys., 2006, 125, 133318). The data demonstrates the importance of O-H bond fission, and that the resulting 4-FPhO co-fragments are formed in a select fraction of their available vibrational state density. All spectra recorded at lambda(phot)> or = 238 nm show a feature centred at TKER approximately 5500 cm(-1). These H atom fragments show no recoil anisotropy, and are rationalised in terms of initial S(1)