No abstract

Direct observations of the solvent induced electronic predissociation of I 2 (B) in liquid CCl 4 are made using femtosecond pump-probe measurements in which fluorescence from spin-orbit excited I*I* pairs, bound by the solvent cage, is used as detection. Data is reported for initial preparations ranging from the B state potential minimum, at 640 nm, to above the dissociation limit, at 490 nm. Analysis is provided through classical simulations, to highlight the role of solvent structure on: recombination, vibrational relaxation, and decay of coherence. The data is consistent with an anisotropic I 2 (X) -CCl 4 potential which, in the first solvent shell, leads to an angular distribution peaked along the molecular axis. The roles of solvent structure and dynamics on electronic predissociation are analyzed. The data in liquid CCl 4 can be understood in terms of a curve crossing near vϭ0, at 3.05 ÅϽR c Ͻ3.8 Å, and the final surface can be narrowed down to 2 g or a(1 g ). This nonadiabatic u→g transition is driven by static and dynamic asymmetry in the solvent structure. The role of solvent structure is demonstrated by contrasting the liquid phase predissociation probabilities with those observed in solid Kr. Despite the twofold increase in density, predissociation probabilities in the solid state are an order of magnitude smaller, due mainly to the high symmetry of the solvent cage. The role of solvent dynamics is evidenced in the energy dependent measurements. Independent of the kinetic energy content in I 2 , electronic predissociation in liquid CCl 4 proceeds with a time constant equal to the molecular vibrational period. A modified Landau-Zener model, in which the effective electronic coupling is taken to be a linear function of vibrational amplitude fits the data, and suggests that cage distortions driven by the molecule enhance its predissociation probability. A nearly quantitative reproduction of the observations is possible when using the recently reported off-diagonal DIM surface that couples the B(0 u ϩ ) and a(1g) states ͓Batista and Coker, J. Chem. Phys. 105, 4033 ͑1996͔͒.

We report the observation of a striking density dependence in the coherence dynamics of an elementary reaction, solute iodine in solvent rare gases density from 0 to 50 mol/l. With the help of MD simulations, the time scales of slow and fast solvent-force fluctuations are resolved and the underlying mechanism is revealed.

Classical molecular dynamics simulations of quantum crystals, using a simple pseudopotential, are reported. The method is implemented for calculating both equilibrium and dynamical properties. As a test, the radial distribution functions for pure solid H 2 and Li doped solid H 2 are computed, and found to be in excellent agreement with prior results obtained by the variational Einstein model ͓D. Li and G. A. Voth, J. Chem. Phys. 96, 5340 ͑1992͔͒. The method also yields a realistic phonon density of states, which is obtained by normal mode analysis. As an implementation in dynamics, the rotational motions of O 2 isolated in solid D 2 are investigated. In agreement with recent experiments, it is found that O 2 does not rotate in solid D 2 .

A one-step catalytic synthesis of 6-substituted 4-phenyl-2-(2'-pyridyl)quinolines provides electronically differentiated ligands without solvent, inert atmosphere, metal contamination, or chromatography. Gold(III) complexes formed from these bidentate PyQuin ligands were characterized and studied by single-crystal X-ray diffraction. The cationic gold(III) chloride synthesized from 6-methoxy-4-phenyl-2-(2'-pyridyl)quinoline has a distorted square-planar ligand environment. Diamagnetic neutral gold(III) complexes from methoxy-, methyl-, and phenyl-PyQuin ligands exhibit a long axial Au-N2 interaction.