Low temperature electron transfer in strongly condensed phase

Electron transfer coupled to a collective vibronic degree of freedom is studied in strongly condensed phase and at lower temperatures where quantum fluctuations are essential. Based on an exact representation of the reduced density matrix of the electronic+reaction coordinate compound in terms of path integrals, recent findings on the overdamped limit in quantum dissipative systems are employed. This allows to give for the first time a consistent generalization of the well-known Zusman equations to the quantum domain. Detailed conditions for the range of validity are specified. Using the Wigner transform these results are also extended to the quantum dynamics in full phase space. As an important application electronic transfer rates are derived that comprise adiabatic and nonadiabatic processes in the low temperature regime including nuclear tunneling. Accurate agreement with precise quantum Monte Carlo data is observed.Comment: 16 pages, 6 figures, revised version with minor change

Solvent-mediated interactions between nanoparticles at fluid interfaces

We investigate the solvent mediated interactions between nanoparticles adsorbed at a liquid-vapor interface in comparison to the solvent mediated interactions in the bulk liquid and vapor phases of a Lennard-Jones solvent. Molecular dynamics simulation data for the latter are in good agreement with results from integral equations in the reference functional approximation and a simple geometric approximation. Simulation results for the solvent mediated interactions at the interface differ markedly from the interactions of the particles in the corresponding bulk phases. We find that at short interparticle distances the interactions are considerably more repulsive than those in either bulk phase. At long interparticle distances we find evidence for a long-ranged attraction. We discuss these observations in terms of interfacial interactions, namely, the three-phase line tension that would operate at short distances, and capillary wave interactions for longer interparticle distances.Comment: 22 pages, 6 figure

Probing Electric Fields in Protein Cavities by Using the Vibrational Stark Effect of Carbon Monoxide

To determine the magnitude and direction of the internal electric field in the Xe4 cavity of myoglobin mutant L29W-S108L, we have studied the vibrational Stark effect of carbon monoxide (CO) using infrared spectroscopy at cryogenic temperatures. CO was photodissociated from the heme iron and deposited selectively in Xe4. Its infrared spectrum exhibits Stark splitting into two bands associated with CO in opposite orientations. Two different photoproduct states can be distinguished, C′ and C″, with markedly different properties. For C′, characteristic temperature-dependent changes of the area, shift, and width were analyzed, based on a dynamic model in which the CO performs fast librations within a double-well model potential. For the barrier between the wells, a height of ∼1.8 kJ/mol was obtained, in which the CO performs oscillations at an angular frequency of ∼25 cm(−1). The magnitude of the electric field in the C′ conformation was determined as 11.1 MV/cm; it is tilted by an angle of 29° to the symmetry axis of the potential. Above 140 K, a protein relaxation leads to a significantly altered photoproduct, C″, with a smaller Stark splitting and a more confining potential (barrier >4 kJ/mol) governing the CO librations