Femtosecond real-time dynamics of solvation : molecular reactions in clusters and supercritical fluids

• Main Author: Liu, Qianli
• Format: Others
• Language: en
• Published: 1997
• Online Access: https://thesis.library.caltech.edu/1291/1/Liu_q_1997.pdf; Liu, Qianli (1997) Femtosecond real-time dynamics of solvation : molecular reactions in clusters and supercritical fluids. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/adkg-dg69. https://resolver.caltech.edu/CaltechETD:etd-04072008-091702 <https://resolver.caltech.edu/CaltechETD:etd-04072008-091702>

This thesis presents two distinct applications of femtosecond laser spectroscopy combined with molecular dynamics (MD) simulations. The first application is the study of the dissociation and geminate recombination dynamics of iodine in argon clusters. By using different size distributions of the clusters in a molecular beam, and tuning the central frequencies of the pump and probe beams, the dynamics over a wide range of energies, states and reaction coordinates have been resolved. A microscopic picture of solvation has been established. The MD simulations in this study have covered the femtosecond to picosecond time scales which are essential for characterizing the evolution of solvation and its equilibration in clusters. The second application is the study of vibrational energy and phase relaxation dynamics of iodine in the gas-to-liquid transition region of rare gases (He, Ne, and Ar). The pressure of the system has been continuously varied from 0 to 4000 bar, allowing the relaxation dynamics to be examined across a wide dynamic range. The usual near-linear density dependence has been found for the energy relaxation rate, while a striking non-linear behavior with density has been discovered for the dephasing rate. The MD simulations in this study adopted both a classical model and a semi-classical model, and have reproduced the experimental observations. The novel density dependence of the dephasing rate is attributed to the combined influence of the solute-solvent forces and the vibration-rotation couplings which have opposite trends with density in the intermediate and high density regimes.