Ultrafast dynamics of o-nitrophenol: An experimental and theoretical study

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DOIResolve DOI: http://doi.org/10.1021/acs.jpca.5b04900
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Journal titleJournal of Physical Chemistry A
Pages92259235; # of pages: 11
SubjectAbsorption spectroscopy; Atmospheric chemistry; Charge transfer; Gases; Ground state; Inorganic acids; Ionization of gases; Phenols; Photoelectron spectroscopy; Photoelectrons; Photolysis; Photons; Proton transfer; Quantum chemistry; Quantum theory; Excited-state proton transfer; Femtosecond transient absorption spectroscopy; Inter-system crossings; Out-of-plane rotation; Photoelectron spectrum; Quantum chemical calculations; Subpicosecond time scale; Time-resolved photoelectron spectroscopy
AbstractThe 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 (S<inf>1</inf>) 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 S<inf>1</inf> state displays strong charge transfer character, which triggers excited state proton transfer from the OH to the NO<inf>2</inf> 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 S<inf>1</inf> and the ground state S<inf>0</inf>. In solution, return to S<inf>0</inf> 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.
Publication date
PublisherAmerican Chemical Society
AffiliationNational Research Council Canada; NRC Steacie Institute for Molecular Sciences; Security and Disruptive Technologies
Peer reviewedYes
NPARC number21276968
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Record identifierce83ef5b-a095-4e1f-85dd-e4e329f4a190
Record created2015-11-10
Record modified2016-05-09
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