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High resolution photofragment translational spectroscopy studies of the ultraviolet photolysis of phenol-d(5)

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Original languageEnglish
Pages (from-to)7984-7993
Number of pages10
JournalJournal of Physical Chemistry A
Volume113
Issue number28
DOIs
DatePublished - 16 Jul 2009

Abstract

The dissociation dynamics of gas phase phenol-d(5) molecules (C6D5OH) following excitation at numerous wavelengths in the range 275 >= lambda(phot) >= 193.3 nm have been investigated using the techniques of H (Rydberg) atom photofragment translational spectroscopy and resonance enhanced multiphoton ionization spectroscopy. The results are compared with those from recent studies of the fully hydrogenated and fully deuterated isotopologues (C6H5OH and C6D5OD), and various halo- and methyl-substituted phenols. Analysis of the vibrational energy disposal within the phenoxyl-d(5) dissociation products identifies three distinct O-H bond fission pathways, involving nonadiabatic coupling to dissociative states of (1)pi sigma* character, following initial pi* <- pi excitation. Dissociation at lambda(phot) > 248 nm involves internal conversion (IC) to high vibrational levels of the electronic ground ((1)pi pi) state and subsequent coupling to the lowest (1)pi sigma* potential energy surface (PES) via a conical intersection (CI) between the (1)pi pi/(1)pi sigma* PESs at extended O-H bond lengths (RO-H). Once lambda(phot) <= 248 nm, dissociation proceeds directly, via a (1)pi pi*/(1)pi sigma* CI. Both pathways yield phenoxyl-d(5) products in selected vibrational levels of the ground ((X) over tilde B-2(1)) electronic state. The detailed energy disposal within the phenoxyl-d(5)((X) over tilde) products shows many parallels with that deduced from companion studies of other phenol isotopologues and various substituted phenols, but a notable isotope effect is identified, thus providing yet greater insights into the factors controlling the vibrational energy disposal in the phenoxyl products. A hitherto unobserved O-H bond fission channel yielding phenoxyl-d(5) fragments in the electronically excited (B) over tilde (2)A(2) state is identified at the shortest excitation wavelength (lambda(phot) = 193.3 nm) and rationalized in terms of nonadiabatic Coupling to, and subsequent dissociation on, the second excited (1)pi sigma* PES. Selective deuteration as in phenol-d(5) causes little reduction in the intensity of the "slower" H atom products that are observed from all phenol systems, suggesting that C-H/D bond fission makes at most a minor contribution to this feature.

    Research areas

  • Computer Simulation, Gases, Phase Transition, Phenol, Photochemistry, Photolysis, Spectrophotometry, Ultraviolet, Spectrum Analysis

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