ANALYSIS OF LOW FREQUENCY VIBRATIONAL PROGRESSIONS IN THE HIGH RESOLUTION ELECTRONIC SPECTRUM of 4,4'-DIMETHYLAMINOBENZONITRILE (DMABN).$^{a}$
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Abstract
Recent developments in the study of the DMABN in the gas $phased^{c,d}$ prompted us to reexamine its electronic spectrum at full rotational resolution. This examination shows that several members of the low frequency vibronic progression at +76, +113, +118, +136, +176, +190, and $+193 cm^{-1}$ are split into two or more components. This splitting, not reported before, is due to the varying magnitude of coupling between two internal $-CH_{3}$ rotors in the DMABN molecule in its different vibrational states. The assignment of the observed spectra was greatly facilitated by the use of genetic algorithm automated assignments.$^{ef}$ Examination of the obtained rotational parameters leads to the determination of the geometry of the molecule in its ground and electronically excited states. There exists a controversy in the literature on the lifetime of the excited electronic state of DMABN between various experiments. The picosecond $study^{g}$ obtained values between 1.5 ps and 24 ps, while the other $works^{h}$ yielded $\sim 5$ ns. From the observed Lorentzian component of the linewidth we determined the lifetime of the excited state to be $4 \pm 0.5 ns.
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^{a}$Work supported by NSF ${^{b}}$Present address: FOM Institute for Plasma Physics Rijnhuizen, Nieuwegein, The Netherlands ${^{c}}$G. Myszkiewicz, G. Berden, W. Leo Meerts, paper TD01 at $58^{th}$ OSU International symposium on molecular spectroscopy ${^{d}}$H. Saigusa, N. Miyakoshi, Ch. Mukai, T. Fukagawa, Sh. Kohtani, R. Nakagaki, and R. Gordon J.Chem.Phys 119, 5414 (2003) ${^{e}}$J. A. Hageman, R. Wehrens, R. de Gelder, W.L. Meerts and L.M.C. Buydens. J. Chem. Phys. 113, 7955 (2000) ${^{f}}$W. L. Meerts, M. Schmitt and G. C. Groenenboom. accepted Can. J. Chem. (2004) ${^{g}}$F. P. Salgado, J. Herbich, A. G. M. Kunst, and R. P. H. Rettschnick, J. Phys. Chem. A 103, 3184 (1999) ${^{h}}$B. R. Howells, J. McCombie, T. F. Palmer, J. P. Simons, and A. Walters J. Chem. Soc., Faraday Trans. 88, 2595 (1992); E. M. Gibson, A. C. Jones, and D. Phillips Chem. Phys. Lett. 136, 454 (1987); E. M. Gibson, A. C. Jones, D. Phillips, A. G. Taylor, W. G. Bouwman, and D. Sandell, J. Phys. Chem. 92, 5449 (1988)
Author Institution: Department of Chemistry, University of Pittsburgh; Department of Molecular and Laser Physics, NSRIM, University of Nijmegen