We have measured fluorescence lifetimes of individual rovibronic levels in SiH2 (Ã 1B1, 020). The lifetimes vary widely from one level to the next, ranging from ≲10 ns to >1 μs. Similar behavior is seen in the (000), (010), and (030) levels. This behavior is interpreted in terms of coupling of the Ã 1B1 rovibronic levels with background levels in the X̃ 1A1 (S0) and ã 3B1 (T1) states, and thence via predissociation to Si(3P)+H2. The irregular variation in the lifetimes reflects the quasirandom spacings of S0 and T1 levels in the vicinity of any particular à state level.

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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 Ã 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.