Roaming isomerization of photoexcited halogenated alkanes in the gas and liquid phases

Tarnovsky, Alexander N.

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https://hdl.handle.net/2142/96992 Copy

Description

Title

Roaming isomerization of photoexcited halogenated alkanes in the gas and liquid phases

Author(s)

Tarnovsky, Alexander N.

Contributor(s)

• Vorobyev, Vasily V.
• Butaeva, Evgeniia V.
• Mereshchenko, Andrey S.
• Hicks, Christopher M.
• Budkina, Darya S.
• Matveev, Sergey M.
• Borin, Veniamin A.

Issue Date

2017-06-20

Keyword(s)

Multiple potential energy surfaces

Abstract

Recent experimental and computational gas-phase studies have brought to light a new type of unimolecular decomposition called a “roaming mechanism. It has only been observed in the gas phase, and whether it also occurs in solution is an intriguing question. Using ultrafast transient absorption spectroscopy, we report direct isomerization of CHBr$_{3}$, BBr$_{3}$, and PBr$_{3}$ geminal tribromides in solution within the first 100 fs after S$_{1}$-excitation. The gas-phase conditions do not affect the earliest course of similar isomerization of CHBr$_{3}$. High-level ab initio simulations on XBr$_{3}$ (X = B, P, and CH) suggest that isomerization is governed by an energetically and dynamically accessible S$_{1}$/S$_{0}$ conical intersection and can be best described as a roaming-mediated pathway. Following the initial relaxation from the Franck-Condon point, “wandering” of the central atoms and migration of Br atom starts on a planar region of the S$_{1}$ surface, and in the vicinity of the conical intersection (~40 fs) the XBr$_{2}$ and Br fragments become separated to $geq$ 3 AA. After passage through the conical intersection, the partially dissociated bromine atom slips off the XBr$_{2}$ bisector plane, and forms the Br–Br bond of the BrXBr–Br isomer (~60 fs). We give examples of similar roaming isomerization in several other di- and polyhalogenated alkanes.

Publisher

International Symposium on Molecular Spectroscopy

Type of Resource

text

Language

eng

Permalink

http://hdl.handle.net/2142/96992

DOI

https://doi.org/10.15278/isms.2017.TG01

Copyright and License Information

Copyright 2017 Alexander N. Tarnovsky

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