Study on the Structure and Vibrational Dynamics of Functional Molecules and Molecular Clusters by Double Resonance Vibrational Spectroscopy

Abstract

Abstract Structure and dynamics of gas-phase molecules and their clusters formed in a supersonic jet has been a great interest to many researchers. Studies on these simple systems provide us with the fundamental concept of many physical and chemical phenomena observed in bulk systems. These studies are also important for the verification of theoretical prediction and quantum chemical calculations. Especially molecular clusters have been thought to be a good model for molecular level understanding of intermolecular interaction and relaxation in condensed phase. However, until the beginning of 1990, studies of molecular clusters mainly concentrated on electronic spectroscopy and very few studies were reported for vibrational spectroscopy. On the other hand, vibrational spectroscopy is essential in condensed phase, and there has been a gap between cluster science and condensed phase science. In 1993 we first reported infrared (IR)–ultraviolet (UV) double resonance spectroscopy of the OH stretching vibration of phenol and its hydrated clusters in a supersonic jet. The observed vibrational spectra showed a characteristic feature of the H-bonding, that is a larger frequency shift as well as broadening of the OH stretching band, and the structures were unambiguously determined with the aid of quantum chemical calculation. It is not too much to say that the combination of double resonance vibrational spectroscopy and quantum chemical calculation has become a very popular method in cluster science. In this paper, we describe various double resonance vibrational spectroscopies in frequency domain. Typical examples of application are shown; determination of H-bonded clusters of benzonitrile, conformer selective vibrational spectroscopy for l-phenylalanine and its hydrated cluster, and study of the encapsulation structure of guest atom and molecules by functional molecules, calixarene and crown ether. Finally, time-domain studies for the dynamics of the vibrations are described. Picosecond IR–UV pump–probe spectroscopy is applied to study the vibrational energy relaxation (VER) of the OH stretching vibration of isolated aromatic molecules and the H-bonded clusters.