%0 DATA
%A Daniel, Murdock
%A Stephanie
J., Harris
%A Ian P., Clark
%A Gregory
M., Greetham
%A Michael, Towrie
%A Andrew J., Orr-Ewing
%A Michael, N. R. Ashfold
%D 2015
%T UV-Induced Isomerization Dynamics
of *N*‑Methyl-2-pyridone in Solution
%U https://acs.figshare.com/articles/journal_contribution/UV_Induced_Isomerization_Dynamics_of_i_N_i_Methyl_2_pyridone_in_Solution/2218381
%R 10.1021/jp511818k.s001
%2 https://ndownloader.figshare.com/files/3854113
%K 3CN
%K S 1 state
%K vibrational absorption spectroscopy
%K ketene
%K data
%K CH
%K NMP
%K SolutionThe photoisomerization dynamics
%K S 1
%K prefulvenic conical intersection
%K molecule
%X The photoisomerization
dynamics of *N*-methyl-2-pyridone
(NMP) dissolved in CH_{3}CN have been interrogated by time-resolved
electronic and vibrational absorption spectroscopy. Irradiation at
two different wavelengths (330 or 267 nm) prepares NMP(S_{1}) molecules with very different levels of vibrational excitation,
which rapidly relax to low vibrational levels of the S_{1} state. Internal conversion with an associated time constant of 110(4)
ps, leading to reformation of NMP(S_{0}) molecules, is identified
as the dominant (>90%) decay pathway. Much of the remaining fraction
undergoes a photoinitiated rearrangement to yield two ketenes (revealed
by their characteristic antisymmetric CCO stretching
modes at 2110 and 2120 cm^{–1}), which are in equilibrium.
The rate of ketene formation is found to be pump-wavelength dependent,
consistent with ab initio electronic structure calculations which
predict a barrier on the S_{1} potential energy surface en
route to a prefulvenic conical intersection, by which isomerization
is deduced to occur. Two kinetic modelsdifferentiated by whether
product branching occurs in the S_{1} or S_{0} electronic
statesare presented and used with equal success in the analysis
of the experimental data, highlighting the difficulties associated
with deducing unambiguous mechanistic information from kinetic data
alone.