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The combination of optical-Kerr-effect (OKE) spectroscopy and molecular dynamics simulations provided with an ability to delve into the librational dynamics of liquids, revealing, in the process, some surprising commonalities among aromic liquids. Benzene and biphenyl, have remarkably similar OKE spectra despite marked differences in their shapes, sizes and moments of inertia-and even more chemically distinct aromatics tend to have noticeable similarities in their spectra.

Chemical reaction dynamics is alwaysa central theme in chemistryresearch. In many important chemical processes, reaction dynamicsis electronically nonadiabatic, i.e., dynamics involves coupled multipleelectronic states. We demonstrate in this paper that a semiclassical(SC) treatment based on an initial value representation methodologyand a classical mapping formalism for the electronic degrees of freedomis now able to provide a rigorous and practical solution to electronicallynonadiabatic dynamics in complex molecular systems. The key componentof this treatment is to incorporate a correlated importance samplingprotocol in nonadiabatic SC calculations, which results in a speedupfactor of 100 or more in comparison with that using the standard samplingapproach. This is illustrated by application to a two-state modelcoupled with up to 10 nuclear bath modes for a benchmark nonadiabaticexcitation energy transfer problem. This work provides great opportunitiesfor the effectively theoretical investigations on reaction mechanismsin complex molecular systems, in which electronically nonadiabaticdynamics plays an importance role. [ABSTRACT FROM AUTHOR]

Experimental and theoretical work on the relaxation of rapidly rotating solutes in liquids have pointed out a number of striking features. Even in rapidly relaxing solvents, the relaxation proceeds quite slowly, exhibiting a manifestly nonlinear response that depends explicitly on the initial rotational energy. In this paper, we show how the long-time behavior, in particular, stems from a strong coupling of solute orientation to local solvent geometry. This coupling creates a rotational friction that decreases sharply with rotational energy, allowing for the protracted survival of not only high-angular-momentum rotational states but the cavity-like low-friction solvent geometries. We show, further, that the slow dynamics is dynamically heterogeneous. The distribution of excited rotors is marked by a distinct population of slowly relaxing hot rotational states. This population can be traced directly to the small subset of liquid configurations that happen to have low rotational friction values at the instant at which the rapid rotation started, indicating an unusual failure of the normally chaotic environment of a liquid to randomize initial conditions.