Ultrafast Dynamics of o-Nitrophenol: An Experimental and Theoretical Study.
The photolysis of o-nitrophenol (o-NP), a typical push-pull molecule, is of current interest in atmospheric chemistry as a possible source of nitrous acid (HONO). To characterize the largely unknown photolysis mechanism, the dynamics of the lowest lying excited singlet state (S1) of o-NP was investigated by means of femtosecond transient absorption spectroscopy in solution, time-resolved photoelectron spectroscopy (TRPES) in the gas phase and quantum chemical calculations. Evidence of the unstable aci-nitro isomer is provided both in the liquid and in the gas phase. Our results indicate that the S1 state displays strong charge transfer character, which triggers excited state proton transfer from the OH to the NO2 group as evidenced by a temporal shift of 20 fs of the onset of the photoelectron spectrum. The proton transfer itself is found to be coupled to an out-of-plane rotation of the newly formed HONO group, finally leading to a conical intersection between S1 and the ground state S0. In solution, return to S0 within 0.2-0.3 ps was monitored by stimulated emission. As a competitive relaxation channel, ultrafast intersystem crossing to the upper triplet manifold on a subpicosecond time scale occurs both in solution and in the gas phase. Due to the ultrafast singlet dynamics, we conclude that the much discussed HONO split-off is likely to take place in the triplet manifold.
Institut für Physikalische Chemie, Karlsruher Institut für Technologie (KIT) , Kaiserstraße 12, 76131 Karlsruhe, Germany.
Hanna A
HA
Ernst
Institut für Physikalische Chemie, Karlsruher Institut für Technologie (KIT) , Kaiserstraße 12, 76131 Karlsruhe, Germany.|Stanford PULSE Institute, SLAC National Accelerator Laboratory , Menlo Park, California 94025, United States.
Thomas J A
TJ
Wolf
AlbaNova University Centre, Stockholm University , Roslagstullsbacken 21, 10691 Stockholm, Sweden.|National Research Council of Canada , 100 Sussex Drive, Ottawa, Ontario K1A 0R6, Canada.
Oliver
O
Schalk
Institut für Physikalische Chemie, Karlsruher Institut für Technologie (KIT) , Kaiserstraße 12, 76131 Karlsruhe, Germany.
Núria
N
González-García
National Research Council of Canada , 100 Sussex Drive, Ottawa, Ontario K1A 0R6, Canada.
Andrey E
AE
Boguslavskiy
National Research Council of Canada , 100 Sussex Drive, Ottawa, Ontario K1A 0R6, Canada.|Departments of Chemistry & Physics, University of Ottawa , 10 Marie Curie, Ottawa, Ontario K1N 6N5 Canada.
Albert
A
Stolow
Institut für Physikalische Chemie, Karlsruher Institut für Technologie (KIT) , Kaiserstraße 12, 76131 Karlsruhe, Germany.
Matthias
M
Olzmann
Institut für Physikalische Chemie, Karlsruher Institut für Technologie (KIT) , Kaiserstraße 12, 76131 Karlsruhe, Germany.
Andreas-Neil
AN
Unterreiner