Structure and dynamics of molecular clusters using picosecond laser spectroscopy

There is much interest in the study of the relationship between structure and dynamics, particularly in van der Waals complexes. Specifically, non-radiative coupling dynamics in xanthione/alkane complexes, as well as vibrational energy transfer and subsequent vibrational predissociation for argon and methane complexes of perylene and 2,5-diphenylfuran (PPF) are examined here. The direct determination of the structure of these complexes is crucial to the understanding of the observed dynamical differences and preliminary experiments in this area were also performed. The time resolved experiments described within were performed using the Time Correlated Single Photon Counting (TCSPC) apparatus and employed a supersonic jet expansion. By measuring fluorescence lifetimes, the rate of non-radiative singlet-triplet coupling in xanthione/alkane complexes was found to depend on the structure of the alkane, as well as its proximity to the C=S chromophore. In studying vibrational predissociation dynamics, argon and methane complexes of preylene were found to exhibit greatly different predissociation dynamics, with the methane predissociating faster than argon. The opposite trend was observed for complementary PPF complexes. The dynamics of the 1:2 perylene/argon complex were found to be dependant on the geometry of the complex. Furthermore, the dynamics associated with the sequential predissociation of two argon atoms from perylene were also studied. Rotational coherence experiments, along with semi-empirical calculations and computer simulations, were used to assign structures to a variety of PPF complexes. Experiments were performed on PPF complexes of argon, methane, n-alkanes and benzene. PPF/methane structures were determined for the 1:1, 1:2 and 1:3 levels of complexation. Two isomeric forms of the PPF/nonane complex were also rotationally resolved. For PPF complexes of hexane and benzene the loss of initially prepared coherence upon vibrational excitation is attributed to rotation-vibration coupling. Thus the relationship between structure and dynamics is directly probed