ISSN:
1089-7690
Source:
AIP Digital Archive
Topics:
Physics
,
Chemistry and Pharmacology
Notes:
In a recent paper (Az I), well-structured T=300 K resonance Raman (RR) profiles for the 1400, 1260, 900, and 2×825 cm−1 lines of azulene in CS2 and for the 825 cm−1 line of azulene in methanol were reported. Previously developed transform techniques were used to (1) compute RR profile line shapes directly from measured optical absorption spectra, and (2) extract ratios of Stokes loss parameters from the line shape scale factors. The transform analysis indicated that (1) our model assumptions (adiabatic and Condon approximations, harmonic phonons, atomic equilibrium position shifts, and small vibrational frequency shifts upon excitation to a single electronic state) are basically correct allowing forminor modifications, and (2) any deviations from these assumptions are likely to be larger for the 900 cm−1 mode and smaller for the 1400 and 1260 cm−1 modes. In this paper (Az II), we report model calculations of the optical absorption spectra, RR profile line shapes, and relative RR intensities. In these calculations, we use a recently proposed nonzero temperature multimode time-correlator modeling procedure. Compared with the conventional sum-over-states method, our time-correlator modeling procedure is superior in that (1) our optical absorption spectra and RR profiles computed via fast Fourier transform techniques have a practically unlimited spectral range and (2) the computing times are short for nonzero temperature multimode calculations. In our basic model, we adopt the assumptions of Az I and use seven azulene modes to obtain simultaneous good fits of the well-structured RR profile line shapes and optical absorption spectra. However, we find that the basic model does not account for the intensity of the 900 cm−1 Raman line relative to that of the 1400 cm−1 line, even though the individual profile line shape fits for these modes are very good. The basic model is therefore modified to allow mixing of the normal coordinates of these two modes. By introducing a single, relatively small mode-mixing parameter, we obtain a good fit of the relative RR intensities in addition to simultaneous detailed fits of the optical absorption spectra and RR profile line shapes. In an alternate approach, we modify our basic model and find that the inclusion of two relatively small non-Condon parameters, instead of one mode mixing parameter, can also produce simultaneous detailed fits of all of our optical absorption and RR data.A comparison of the two modified models solely on the basis of simplicity favors the mode-mixing model, since only one extra parameter is required to modify our basic model.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.448700
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