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Effects of Ring Fluorination on the Ultraviolet Photodissociation Dynamics of Phenol

Cooper, GA; Cobbin, MR; Ashfold, MNR; (2020) Effects of Ring Fluorination on the Ultraviolet Photodissociation Dynamics of Phenol. Journal of Physical Chemistry A , 124 (47) pp. 9698-9709. 10.1021/acs.jpca.0c08927. Green open access

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Abstract

The dynamics of photoinduced O-H bond fission in five fluorinated phenols (2-fluorophenol, 3-fluorophenol, 2,6-difluorophenol, 3,4,5-trifluorophenol, and pentafluorophenol) have been investigated by H Rydberg atom photofragment translational spectroscopy following excitation at many wavelengths in the range 220 ≤ λ ≤ 275 nm. The presence of multiple fluorine substituents reduces the efficiency of O-H bond fission (by tunneling) from the first excited (11π π) electronic state, whereas all bar the perfluorinated species undergo O-H bond fission when excited at shorter wavelengths (to the 21π π∗ state). As in bare phenol, O-H bond fission is deduced to occur by non-adiabatic coupling at conical intersections between the photoprepared "bright"π π∗ states and the 11πσ∗ potential energy surface. In all cases, the fluorophenoxyl photoproducts are found to be formed in a range of vibrational levels, all of which include an odd number of quanta (typically one) in an out-of-plane (a″) vibrational mode; this product vibration is viewed as a legacy of the parent out-of-plane motions that promote non-adiabatic coupling to the dissociative 11πσ∗ potential. The radical products also show activity in in-plane vibrations involving coupled (both in- and out-of-phase) C-O and C-F wagging motions, which can be traced to the impulse between the recoiling O and H atoms and, in detail, are sensitive to the presence (or not) of an intramolecular F···H-O hydrogen bond. Upper limit values for the O-H bond dissociation energies are reported for all molecules studied apart from pentafluorophenol.

Type: Article
Title: Effects of Ring Fluorination on the Ultraviolet Photodissociation Dynamics of Phenol
Location: United States
Open access status: An open access version is available from UCL Discovery
DOI: 10.1021/acs.jpca.0c08927
Publisher version: https://doi.org/10.1021/acs.jpca.0c08927
Language: English
Additional information: This version is the author accepted manuscript. For information on re-use, please refer to the publisher’s terms and conditions.
Keywords: Aromatic compounds, Energy, Molecules, Photodissociation, Quantum mechanics
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Chemistry
URI: https://discovery.ucl.ac.uk/id/eprint/10171449
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