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Ultrafast charge transfer via a conical intersection in dimethylaminobenzonitrile

MPG-Autoren
http://pubman.mpdl.mpg.de/cone/persons/resource/persons60499

Fuß,  Werner
Laser Chemistry, Max Planck Institute of Quantum Optics, Max Planck Society;
Laboratory for Attosecond Physics, Max Planck Institute of Quantum Optics, Max Planck Society;

Pushpa,  Kumbil Kutta
Max Planck Society;

http://pubman.mpdl.mpg.de/cone/persons/resource/persons60822

Schmid,  Wolfram E.
Laser Chemistry, Max Planck Institute of Quantum Optics, Max Planck Society;

http://pubman.mpdl.mpg.de/cone/persons/resource/persons60889

Trushin,  Sergei A.
Laboratory for Attosecond Physics, Max Planck Institute of Quantum Optics, Max Planck Society;
Laser Chemistry, Max Planck Institute of Quantum Optics, Max Planck Society;

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Zitation

Fuß, W., Pushpa, K. K., Rettig, W., Schmid, W. E., & Trushin, S. A. (2002). Ultrafast charge transfer via a conical intersection in dimethylaminobenzonitrile. Photochemical & Photobiological Sciences, 1(4), 255-262. Retrieved from http://www.rsc.org/CFmuscat/intermediate_abstract.cfm?FURL=/ej/PP/2002/b111678a.PDF.


Zitierlink: http://hdl.handle.net/11858/00-001M-0000-000F-C229-2
Zusammenfassung
The La-like S2 state (2A) of 4-(dimethylamino)benzonitrile was pumped at 267 nm in the gas phase at 130 degrees C. Nonresonant multiphoton ionization at 800 nm with mass-selective detection then probed the subsequent processes. Whereas ionization at the Franck-Condon geometry only gave rise to the parent ion, fragmentation increased on motion towards the charge-transfer (CT) state. This useful difference is ascribed to a geometry-dependent resonance in the ion. The time constants found are interpreted by ultrafast (approximate to 68 fs) relaxation through a conical intersection to both the CT and the Lb-type S1 state (1B). Then the population equilibrates between these two states within 1 ps. From there the molecule relaxes within 90 ps to a lower excited state which can only be a triplet state (T-n) and then decomposes within 300 ps. Previous experiments either investigated only 1B-->CT relaxation-which does not take place in the gas phase or nonpolar solvents for energetic reasons-or, starting from S2 excitation, typically had insufficient time resolution (>1 ps) to detect the temporary charge transfer. Only recently temporary population of the CT state was found in a nonpolar solvent (Kwok et al., J Phys. Chem. A, 2000, 104, 4188), a result fully consistent with our mechanism. We also show that S2-->S1 relaxation does not occur vertically but involves an intermediate strong geometrical distortion, passing through a conical intersection.