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Investigation of short-time isomerization dynamics in p-nitroazobenzene from resonance Raman intensity analysis

Biswas, Nandita and Abraham, Becky and Umapathy, Siva (2002) Investigation of short-time isomerization dynamics in p-nitroazobenzene from resonance Raman intensity analysis. In: Journal of Physical Chemistry A, The, 106 (41). pp. 9397-9406.

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Official URL: http://pubs.acs.org/doi/abs/10.1021/jp0108162


Resonance Raman (RR) spectra are presented for p-nitroazobenzene dissolved in chloroform using 18 excitation Wavelengths, covering the region of (1)(n --> pi*) electronic transition. Raman intensities are observed for various totally symmetric fundamentals, namely, C-C, C-N, N=N, and N-O stretching vibrations, indicating that upon photoexcitation the excited-state evolution occurs along all of these vibrational coordinates. For a few fundamentals, interestingly, in p-nitroazobenzene, it is observed that the RR intensities decrease near the maxima of the resonant electronic (1)(n --> pi*) transition. This is attributed to the interference from preresonant scattering due to the strongly allowed (1)(pi --> pi*) electronic transition. The electronic absorption spectrum and the absolute Raman cross section for the nine Franck-Condon active fundamentals of p-nitroazobenzene have been successfully modeled using Heller's time-dependent formalism for Raman scattering. This employs harmonic description of the lowest energy (1)(n --> pi*) potential energy surface. The short-time isomerization dynamics is then examined from a priori knowledge of the ground-state normal mode descriptions of p-nitroazobenzene to convert the wave packet motion in dimensionless normal coordinates to internal coordinates. It is observed that within 20 fs after photoexcitation in p-nitroazobenzene, the N=N and C-N stretching vibrations undergo significant changes and the unsubstituted phenyl ring and the nitro stretching vibrations are also distorted considerably.

Item Type: Journal Article
Publication: Journal of Physical Chemistry A, The
Publisher: American Chemical Society
Additional Information: Copyright of this article belongs to American Chemical Society.
Department/Centre: Division of Chemical Sciences > Inorganic & Physical Chemistry
Date Deposited: 19 Jul 2011 10:05
Last Modified: 19 Jul 2011 10:05
URI: http://eprints.iisc.ac.in/id/eprint/39252

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