Spectroscopy and dynamics of molecular clusters: van der Waals complexes to hydrogen bonded systems

Several types of laser spectroscopy have been used to study the spectroscopy and dynamics of supersonically cooled atoms and molecules in the gas phase over the course of my graduate studies. They are resonance enhanced multiphotonionization spectroscopy, zero electron kinetic energy spectroscopy, mass analyzed threshold ionization spectroscopy and UV-UV hole burning spectroscopy.;On van der Walls complexes, the binding energies and the dissociation dynamics, e.g., in aniline+-(argorn)1,2, benzodioxan +-(argon)1,2 have been studied. For the first time the dissociative isomerization process is observed upon dissociation of photo-created aniline+-argon)2 complex and the relative energies in pi bonded versus H bonded aniline+-argon species has been determined, which can be compared to their neutral counterparts.;On the biologically relevant molecules of tryptophol and tryptamine, the conformer specific cationic spectroscopy in these tryptophan analogs has been studied. As it turns out, the resulted threshold photoelectron spectra are extremely sensitive to the geometric changes upon ionization in the molecules where multiple isomers are present. The dissociative isomerization process is observed in hydrogen bonded water cluster of tryptamine+-H 2O, as determined by a standard photoionization fragmentation approach.;On the molecule of 9-Hydroxy-9-fluorenecarboxylic acid which has multiple intramolecular hydrogen bonds, the S1 ← S0 electronic spectrum has been obtained on the monomer and single isomer in the neutral is revealed to be present in the gas phase. S1 ← S0 electronic spectroscopy on the clusters of formic acid, benzoic acid, acetic acid, water and formamide has also been measured and their structures on the neutral ground state and S1 excited state have been compared to the monomer counterpart. For the first time the threshold photo ionization spectra of the clusters of formic acid, benzoic acid and acetic acid have been successfully measured where multiple intra/inter molecular hydrogen bonds are involved in the clusters.;In addition, the triplet states of argon atoms created through a novel pulsed high voltage discharge of supersonic argon gas have been studied using laser spectroscopy and an unusual electric quadrupole transition in argon atoms is unambiguously assigned, which was initially observed in the stark map experiments.