Condensed-phase Dynamics

The beauty of the prior approximations is that by assuming a mean-field influence of solvation we can continue to work in a phase space having the same dimensionality as that for the gas phase that being the case, analysis using the tools of TST is mechanically identical for the two phases. When the solvent is not fully equilibrated with the complete reaction path, however, the reacting system can no longer legitimately be described exclusively in terms of solute coordinates. 

Note that the region where solvent is least well equilibrated to the solute is expected to be in the vicinity of the activated complex, since it has so short a lifetime. Since non-equilibrium solvation is less favorable than equilibrium solvation, the non-equilibrium free energy of the activated complex is higher than the equilibrium free energy, and the non-equilibrium lag in solvent response thus slows the reaction. This effect is sometimes referred to as solvent friction and can be accounted for by inclusion in the transmission factor a. 

Explicit inclusion of all solvent degrees of freedom, e.g., in an MD simulation, is not a very effective approach to modeling the non-equilibrium solvent influence, however. One 

---

With the wealth of infonnation contained in such two-dimensional data sets and with the continued improvements in technology, the Raman echo and quasi-echo techniques will be the basis for much activity and will undoubtedly provide very exciting new insights into condensed phase dynamics in simple molecular materials to systems of biological interest. 

In practice these experiments are very difficult and expensive, and have typically been applied to systems such as liquid benzene (33). On the encouraging side, it should be noted that these techniques are indeed applicable to condensed-phase systems and are extremely informative concerning fundamental condensed-phase dynamics. 

Using photoelectron detection in a femtochemistry arrangement, we studied size-selected clusters of ionic systems, covering the transition from gas phase to condensed phase dynamics [6]. We investigated the solvent effect on Oj dissociation dynamics, and observed... 

In summary, the presented results demonstrate the capacity of combining IR-pump-probe methods with calculations on microsolvated base pairs to reveal information on hidden vibrational absorption bands. The simulation of real condensed phase dynamics of HBs, however, requires to take into account all intra- and intermolecular interactions mentioned in the Introduction. As far as DNA is concerned, Cho and coworkers have given an impressive account on the dynamics of the CO fingerprint modes [22-25]. Promising results for a single AU pair in deuterochloroform [21] have been reported recently using a QM/MM scheme [65]. 

The theoretical foundation for reaction dynamics is quantum mechanics and statistical mechanics. In addition, in the description of nuclear motion, concepts from classical mechanics play an important role. A few results of molecular quantum mechanics and statistical mechanics are summarized in the next two sections. In the second part of the book, we will return to concepts and results of particular relevance to condensed-phase dynamics. 

However, Eq. (4.1) has another advantage in that it directly connects to the system-bath models used in condensed phase dynamics [38]. Here the reactive coordinates and the substrate modes comprise the relevant system and the bath, respectively. Larger molecules may provide their own bath and Eq. (4.1) can be used to calculate an ah initio system-bath Hamiltonian and microscopic relaxation and dephasing rates [33]. 

This work was supported in part at both Pacific Northwest National Laboratory (PNNL) and the University of Minnesota (UM) by the Division of Chemical Sciences, Office of Basic Energy Sciences, U. S. Department of Energy (DOE), and it was supported in part (condensed-phase dynamics) at the University of Minnesota by the National Science foundation. Battelle operates PNNL for DOE. 

Using photoelectron detection in a femtochemistry arrangement, we studied size-selected clusters of ionic systems, covering the transition from gas phase to condensed phase dynamics [6]. We investigated the solvent effect on Oj dissociation dynamics, and observed that the addition of one solvent (O2, N2, Xe or N2O) gives very different effects on the dynamics of the nuclear motion, whose wave packet bifurcates in two channels. These real time studies of the one-solvent dynamics provide the time scale of the distinctive processes of electron recombination and bond rupture, and vibrational predissociation— with both... 

In condensed-phase dynamics, we are typically interested in the detailed behavior of just a small part of a large system, so we partition the total system into the subsystem of interest, s, and a surrounding bath, b. The total Hamiltonian is then written... 

Condensed phase dynamics such as electron and energy transfer are an important subject in quantum dissipative mechanics. It treats an arbitrary system (Hs) embedded in bath that assumes to be harmonic, hB= J2jt coj pj + xj). The total composite Hamiltonian assumes the form of ... 

Smith, N. A. Meech, S. R (2002). Optically-heterodyne-detected optical Kerr effect (OHD-OKE) applications in condensed phase dynamics. International Reviews in Physical Chemistry, 21,75-100... 

---