Electronic Spectroscopy Of Ethynylbenzyl Chromophores

Reilly, Neil J.

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https://hdl.handle.net/2142/116932 Copy

Description

Title

Electronic Spectroscopy Of Ethynylbenzyl Chromophores

Author(s)

Reilly, Neil J.

Contributor(s)

• Hewett, Daniel M.
• Ruscitti, Massimo
• Khani, Sima
• Ross, Sederra D.
• Flores, Jonathan

Issue Date

2022-06-22

Keyword(s)

Mini-symposium: Spectroscopy meets Chemical Dynamics

Abstract

The indenyl and phenylpropargyl radicals are the most stable isomers of C$_9$H$_7$ and have emerged as ubiquitous products in flames and hydrocarbon discharges. The \textit{o-}, \textit{m-}, and \textit{p-} ethynylbenzyl isomers lie \textit{ca.} 150-160\,kJ/mol and 20-30\,kJ/mol above the 1-indenyl and 1-phenylpropargyl minima, respectively, and can presumably form by barrierless addition of CH radical to phenylacetylene, but they are thoroughly unexamined spectroscopically. We have recently observed the $D_0-D_1$ optical transitions of the \textit{para} and \textit{meta} variants by resonant two-color two-photon ionization and laser-induced fluorescence\,/\,dispersed fluorescence spectroscopy. For the \textit{para} form, extension of the benzyl chromophore by a C$_2$ unit engenders a relatively (w.r.t. benzyl) strong transition that can in large part be rationalized on Franck-Condon premises; while most of the vibronic structure in the much weaker transition of the \textit{meta} isomer arises from intensity-borrowing among totally symmetric modes that are only weakly FC-active. Modes of $a_1$ symmetry of \textit{para}-ethynylbenzyl are subject to pervasive Fermi resonances, as is established by DF spectroscopy. In the jet-cooled discharge, both \textit{para} and \textit{meta} forms are found in coexistence with 1-phenylpropargyl (which one might call $\alpha$-ethynylbenzyl) at levels that cannot be explained by putative sample impurities unless computed oscillator strengths are too small by several orders of magnitude, suggesting rearrangement of all three radicals \textit{via} an intermediate that remains unobserved. The \textit{para} form has not been detected at the time of writing, perhaps because it cyclizes to indenyl.

Publisher

International Symposium on Molecular Spectroscopy

Type of Resource

text

Language

eng

Handle URL

https://hdl.handle.net/2142/116932

DOI

https://doi.org/10.15278/isms.2022.WA08

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Copyright 2022 held by the authors

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