Rydberg excited iodine-argon van der Waals complexes studied by resonance enhanced multiphoton ionization spectroscopy High resolution threshold photoelectron spectroscopy of aniline and aniline van der Waals complexes Suppression of fragment contributions to massselected resonance enhanced multiphoton ionization spectra of van der Waals clustersThe origin region of the SI +-So transitions of the aniline-Ar 3 , aniline-Ar 4 , and aniline-Ars molecules have been measured using mass selected resonance enhanced, multi photon ionization (REMPI) spectroscopy. The aniline-Ar 3 spectrum exhibits two distinct groups of peaks. The more prominent group displays a regular vibrational progression, with five obvious members and a spacing of ~ 16 cm -I. Vibrational structure in the other group is less distinctive. On the basis of cluster potential calculations described in this paper, we believe that two stable aniline-(argon) 3 isomers exist in the supersonic expansion and that the two groups of peaks correspond to absorption by these two isomers. Spectra recorded at masses corresponding to aniline-(argon)4 and aniline-(argon)s display broadened structure that probably reflects contributions from larger aniline-(argon) n clusters which fragment upon ionization. There is, however, some evidence for a progression with a spacing of ~ 16 cm -I in the aniline-(argon)4 spectrum. Dispersed fluorescence spectra from relatively small aniline-Ar n clusters (4 < n < 10) indicate that vibrational redistribution from Franck-Condon active van der Waals modes occurs with rates of at least 5 X 10'1 S -I.
Ionic clusters consisting of a polyatomic ion surrounded by a few 'solvent' atoms or molecules, provide a connecting link between the isolated gas phase ion and the ion solvated in a condensed medium. Analysis of the vibrational structure associated with the motion of the cluster atoms can reveal details concerning the intermolecular potential. However, for large polyatomic ions, information concerning the cluster vibrational motion has been difficult to obtain using conventional spectroscopic methods. We have developed a new combination of the previously available techniques of supersonic cooling, resonance-enhanced multi photon ionisation, timeof- flight mass spectroscopy, in concert with one-photon photodissociation spectroscopy. This new technique takes advantage of the facile predissociation of an electronically excited cluster and affords us a method of studying the previously unmeasurable vibrational structure associated with the motion of a molecular cluster ion. Using this technique we have obtained vibrationally resolved photodissociation spectra of a number of aromatic-rare gas cluster ions. Analysis of their vibrational structure permits structural details of the cluster cation to be deduced.
The photophysics of silylene (SiH2), formed during the infrared multiphoton dissociation (IRMPD) of organosilanes, is investigated using photofragmentation excitation spectroscopy (PHOFEX). Silylene molecules are formed in the X̃ 1A1(000) ground state via IRMPD of n-butylsilane. Laser induced fluorescence (LIF) is used to detect ground state (3p2 3P0) Si atoms following rovibronically resolved photoexcitation of SiH2 to the à 1B1(0v20) state. Variations in Si atom production are measured simultaneously with the SiH2 excitation spectrum, allowing comparisons to be made between Si yield and the rovibronic structure in the SiH2 1B1 manifold. We have examined the correlation between the widely varying fluorescence lifetimes of the individual rovibronic states of SiH2 and the relative yields of Si production. The presence of additional Si precursors in the primary dissociation process is suggested. Mechanisms for Si release following IRMPD of n-butylsilane and electronic excitation of SiH2 are developed and discussed.
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