dc.contributor |
Ministerio de Economía y Competitividad (Espanya) |
dc.contributor.author |
Trachsel, Maria A. |
dc.contributor.author |
Wiedmer, Timo |
dc.contributor.author |
Blaser, Susan |
dc.contributor.author |
Frey, Hans-Martin |
dc.contributor.author |
Li, Quansong |
dc.contributor.author |
Ruiz-Barragán, Sergi |
dc.contributor.author |
Blancafort San José, Lluís |
dc.contributor.author |
Leutwyler, Samuel |
dc.date |
2017-02-02T12:39:18Z |
dc.date |
2017-02-02T12:39:18Z |
dc.date |
2016-09-01 |
dc.identifier.citation |
0021-9606 (versió paper) |
dc.identifier.citation |
1089-7690 (versió electrònica) |
dc.identifier.citation |
026114 |
dc.identifier.uri |
http://hdl.handle.net/10256/13493 |
dc.format |
application/pdf |
dc.language.iso |
eng |
dc.publisher |
American Institute of Physics (AIP) |
dc.relation |
https://doi.org/10.1063/1.4964091 |
dc.relation |
MINECO/PE 2015-2017/CTQ2015-69363-P |
dc.relation |
Reproducció digital del document publicat a: https://doi.org/10.1063/1.4964091 |
dc.relation |
© Journal of Chemical Physics, 2016, vol. 145, núm. 13, p. 134307 |
dc.relation |
Articles publicats (D-Q) |
dc.rights |
Tots els drets reservats |
dc.rights |
info:eu-repo/semantics/openAccess |
dc.subject |
Ionització |
dc.subject |
Ionization |
dc.subject |
Radiació ultraviolada |
dc.subject |
Ultraviolet radiation |
dc.title |
The excited-state structure, vibrations, lifetimes, and nonradiative dynamics of jet-cooled 1-methylcytosine |
dc.type |
info:eu-repo/semantics/article |
dc.type |
info:eu-repo/semantics/publishedVersion |
dc.description.abstract |
We have investigated the S0 → S1 UV vibronic spectrum and time-resolved S1 state dynamics of
jet-cooled amino-keto 1-methylcytosine (1MCyt) using two-color resonant two-photon ionization,
UV/UV holeburning and depletion spectroscopies, as well as nanosecond and picosecond timeresolved
pump/delayed ionization measurements. The experimental study is complemented with
spin-component-scaled second-order coupled-cluster and multistate complete active space second
order perturbation ab initio calculations. Above the weak electronic origin of 1MCyt at 31 852 cm−1
about 20 intense vibronic bands are observed. These are interpreted as methyl group torsional
transitions coupled to out-of-plane ring vibrations, in agreement with the methyl group rotation
and out-of-plane distortions upon 1ππ∗ excitation predicted by the calculations. The methyl torsion
and ν′1 (butterfly) vibrations are strongly coupled, in the S1 state. The S0 → S1 vibronic spectrum
breaks off at a vibrational excess energy Eexc ∼ 500 cm−1, indicating that a barrier in front of the
ethylene-type S1 S0 conical intersection is exceeded, which is calculated to lie at Eexc = 366 cm−1.
The S1 S0 internal conversion rate constant increases from kIC = 2 · 109 s−1 near the S1(v = 0)
level to 1 · 1011 s−1 at Eexc = 516 cm−1. The 1ππ∗ state of 1MCyt also relaxes into the lower-lying
triplet T1 (3ππ∗) state by intersystem crossing (ISC); the calculated spin-orbit coupling (SOC) value
is 2.4 cm−1. The ISC rate constant is 10–100 times lower than kIC; it increases from kISC = 2 · 108 s−1
near S1(v = 0) to kISC = 2 · 109 s−1 at Eexc = 516 cm−1. The T1 state energy is determined from the
onset of the time-delayed photoionization efficiency curve as 25 600 ± 500 cm−1. The T2 (3nπ∗)
state lies >1500 cm−1 above S1(v = 0), so S1 T2 ISC cannot occur, despite the large SOC
parameter of 10.6 cm−1. An upper limit to the adiabatic ionization energy of 1MCyt is determined
as 8.41 ± 0.02 eV. Compared to cytosine, methyl substitution at N1 lowers the adiabatic ionization
energy by ≥0.32 eV and leads to a much higher density of vibronic bands in the S0 → S1 spectrum.
The effect of methylation on the radiationless decay to S0 and ISC to T1 is small, as shown by
the similar break-off of the spectrum and the similar computed mechanisms |
dc.description.abstract |
This research has been supported by the Schweiz. Nationalfonds (Grant Nos. 121993 and 132540), the Agència de Gestió d’Ajuts Universitaris i de Recerca (AGAUR) from Catalonia (Spain) (Grant No. 2014SGR1202), the Ministerio de Economía y Competividad (MINECO) from Spain (Grant No. CTQ2015-69363-P), and the National Natural Science Foundation of China (Grant No. 21303007) |