The Relation of VPIE to Condensed Phase Molecular Properties and Vibrational Dynamics [Pg.144]

Owrutsky JC, Li M, Culver JP, Sarisky MJ, Yodh AG, Hochstrasser RM. Vibrational dynamics of condensed phase molecules studied by ultrafast infrared spectroscopy. In Lau A, Siebert F, Werncke W, eds. Time Resolved Vibrational Spectroscopy IV. Berlin Springer-Verlag, 1993 63-67. [Pg.360]

Statistical mechanics computations are often tacked onto the end of ah initio vibrational frequency calculations for gas-phase properties at low pressure. For condensed-phase properties, often molecular dynamics or Monte Carlo calculations are necessary in order to obtain statistical data. The following are the principles that make this possible. [Pg.12]

It is clear that a number of questions need to be answered. Why, in the condensed phase, is the intersystem crossing between two nn states so efficient What is the explanation of the conflict between the linewidth studies of Dym and Hochstrasser and the lifetime studies of Rentzepis and Busch, with respect to the vibrationally excited levels It was in an attempt to provide some answers to these questions that Hochstrasser, Lutz and Scott 43 carried out picosecond experiments on the dynamics of triplet state formation. In benzene solution the build up of the triplet state had a lifetime of 30 5 psec, but this could only be considered as a lower limit of the intersystem crossing rate since vibrational relaxation also contributed to the radiationless transition to the triplet state. The rate of triplet state build-up was found to be solvent-dependent. [Pg.128]

In contrast to the subsystem representation, the adiabatic basis depends on the environmental coordinates. As such, one obtains a physically intuitive description in terms of classical trajectories along Born-Oppenheimer surfaces. A variety of systems have been studied using QCL dynamics in this basis. These include the reaction rate and the kinetic isotope effect of proton transfer in a polar condensed phase solvent and a cluster [29-33], vibrational energy relaxation of a hydrogen bonded complex in a polar liquid [34], photodissociation of F2 [35], dynamical analysis of vibrational frequency shifts in a Xe fluid [36], and the spin-boson model [37,38], which is of particular importance as exact quantum results are available for comparison. [Pg.389]

The instanton method takes into account only the dynamics of the lowest energy doublet. This is a valid description at low temperature or for high barriers. What happens when excitations to higher states in the double well are possible And more importantly, the equivalent of this question in the condensed phase case, what is the effect of a symmetrically coupled vibration on the quantum Kramers problem The new physical feature introduced in the quantum Kramers problem is that in addition to the two frequencies shown in Eq. (28) there is a new time scale the decay time of the flux-flux correlation function, as discussed in the previous Section after Eq. (14). We expect that this new time scale makes the distinction between the comer cutting and the adiabatic limit in Eq. (29) to be of less relevance to the dynamics of reactions in condensed phases compared to the gas phase case. [Pg.79]

Another important breakthrough occurred with the 1974 development by Laubereau et al. (36) of intense tunable ultrashort mid-IR pulses. IR excitation is more selective and reliable than SRS, so SRS pumping is hardly ever used any more. At present the most powerful methods for studying VER in condensed phases use IR pump pulses. The most common (and complementary) techniques to probe nonequilibrium vibrational dynamics induced with mid-IR pump pulses are anti-Stokes Raman probing (the IR-Raman method) or IR probing (IR pump-probe experiments). [Pg.553]

VER occurs as a result of fluctuating forces exerted by the bath on the system at the system s oscillation frequency (22). We will use the upper-case to denote the system s vibrational frequency and lower-case co to denote other vibrations. It may also be useful to look at fluctuating forces exerted on a particular chemical bond (23). Fluctuating forces are characterized by a force-force correlation function. The Fourier transform of this force correlation function at Q, denoted rj(Q), characterizes the quantum mechanical frequency-dependent friction exerted on the system by the bath (19,22). This friction, especially at higher (i.e., vibrational) frequencies, plays an essential role in condensed phase chemical reaction dynamics (24,25). [Pg.552]

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