Ionization energies and single vibronic level emission (SVLE) spectroscopy of cis- and trans-1-vinylpropargyl radicals

Reilly, Neil J.

Permalink

https://hdl.handle.net/2142/104470 Copy

Description

Title

Ionization energies and single vibronic level emission (SVLE) spectroscopy of cis- and trans-1-vinylpropargyl radicals

Author(s)

Reilly, Neil J.

Contributor(s)

• Ross, Sederra D.
• Ward, Meredith
• Flores, Jonathan

Issue Date

2019-06-21

Keyword(s)

Radicals

Abstract

The resonance-stabilized 1-vinylpropargyl radical (1vpr), which can adopt \emph{cis-} and \emph{trans-} conformations, is held to be a significant intermediate in hydrocarbon pyrolysis and has also been observed in the crossed-beam reaction of C$_2$ with propyne. We have cleanly generated 1vpr in a discharge of pent-1-ene-4-yne and measured the adiabatic ionization energy (AIE) of each conformer by two-colour ion-yield spectroscopy. Our work takes advantage of an earlier report by one of us of the 1vpr electronic origin bands near 460\,nm and 470\,nm. Extrapolation to zero-field yields AIEs of 7.823(1)\,eV and 7.894(1)\,eV for the \emph{trans-} and \emph{cis-} forms respectively, in superb agreement with a QCISD(T) calculation (Hansen \emph{et al.}, J. Phys. Chem. A 2006, 110, 4376-4388), and further supporting the identification of 1vpr in flames. As part of on-going work, we have also secured vibrational assignments for a number of levels in the ground and first excited states of both conformers, first by decomposing the mass-resolved electronic spectrum (as much as possible) into \emph{cis-} and \emph{trans-} contributions using hole-burning spectroscopy, and then by measuring SVLE spectra for sufficiently well-resolved bands. The apparent projection of a low-frequency excited state mode onto both $a'$ and $a''$ levels in the ground state is taken as evidence of a Duschinsky rotation that mixes $a'$ and $a''$ modes, and perhaps, therefore, of some reduction in planarity in the excited state, particularly for the \emph{cis} isomer. The extent to which this interpretation is reflected by B3LYP and CASSCF calculations will be discussed.

Publisher

International Symposium on Molecular Spectroscopy

Type of Resource

text

Language

eng

Permalink

http://hdl.handle.net/2142/104470

DOI

https://doi.org/10.15278/isms.2019.FD05

Copyright and License Information

Copyright 2019 Neil J. Reilly

Owning Collections