Ultrasensitive dye laser photoacoustic spectra have been obtained for CH and CD stretch overtone excitations of gas phase benzene (C6H6, C6D6, C6HD5), toluene, and fluorobenzenes (C6H5F, C6HF5) in the visible and near infrared spectral regions. Interpretations of the spectral observables (band positions, intensities, and widths) clarify the nature and dynamics of highly vibrationally excited states in benzene and related polyatomic molecules: (1) the states we initially prepare by direct one-photon absorption involve highly localized and selective excitations of CH (CD) bond mode sites; (2) these localized excitations cause dynamical symmetry lowering of the molecular systems; and (3) ultrarapid (i.e., subpicosecond) temporal evolution occurs by highly nonstatistical intramolecular rate processes. Analyses of the energy and state dependence of overtone bandwidths support a mechanistic picture in which sequential state-to-state decays are the preferred dynamical pathways for intramolecular vibrational energy redistribution.

[reaction: see text] A copper-mediated deracemization of the vaulted biaryl ligands VANOL and VAPOL can be readily achieved in the presence of (-)-spartiene. The optimal procedure involves the in situ generation of copper(II) and leads to the reproducible formation of (S)-VANOL and (S)-VAPOL in greater than 99% ee from the racemates. This method is superior to existing procedures for BINOL (92% ee).

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Radiationless transition in large isolated molecules: Variation of excess energy dependence of its decay rate with initially prepared electronic state A general scheme for calculating relative nonradiative decay rates of initially selected vibronic levels in polyatomic molecules is developed. Here we are concerned only with relative rates corresponding to initial vibronic states in some particular electronic manifold decaying into some other particular electronic manifold. Therefore we need only consider the exact density-of-states-weighted-Franck-Condon factor accounting for the vibrational contribution to the over-all nonradiative decay rate. This contribution is calculated approximately in the large molecule (statistical) limit by deriving the appropriate (modified) energy gap law. The contributions of "special" modes (e.g., optically excited modes, and modes with large geometry and/or frequency shifts) are partitioned from those of the other modes by techniques similar to ones developed earlier to treat cis-trans isomerism and are calculated explicitly. Excellent agreement with the recent low pressure experimental results of Spears, Abramson, and Rice for the S,--+T, intersystem crossing rates from individual vibronic states in benzene and perdeuterobenzene is obtained, but only by taking proper account of the effects of geometry and frequency changes of the various vibrational modes involved in the transition. The sharp dependence of the relative nonradiative rates for a progression in an optical mode upon the frequency shift in that mode leads to the possibility of evaluating the vibrational frequencies in an electronic state by measuring the radiationless decay rate into that electronic state (e.g., in the benzene case determining T, vibrational frequencies from S,--+T, decay rates). Finally, we comment upon recent low pressure experimental results for /3-naphthylamine, monofluorobenzene, and upon some observed temperature dependences of radiationless transition rates in matrices.