Wide fluctuations in fluorescence lifetimes of individual rovibronic levels in SiH2 (Ã 1B1)

Abstract

We have measured fluorescence lifetimes of individual rovibronic levels in SiH2 (à 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 à 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.

Absorption spectroscopy of SiH2 near 640 nm

“…4 of Ref. 6. This transition, which is weaker than those previously studied, is particularly important as it allows the determination of the geometry and of the energy of the vibrationless level of the à 1 B 1 electronic state.…”

“…The strong rotational perturbations in the à 1 B 1 state have been related 4 to the unusual radiative lifetimes recently measured by laser-induced fluorescence ͑LIF͒ by Thoman, Steinfeld and coworkers. 5,6 In the 1 A 1 state, Yamada et al 10 studied the 2 band by means of an infrared diode laser spectrometer, thus providing the only high resolution infrared data available for this radical up to this moment. Several authors have reported the LIF detection of silylene produced by multiphoton or UV dissociation of silane compounds.…”

“…Several authors have reported the LIF detection of silylene produced by multiphoton or UV dissociation of silane compounds. 5,6,[11][12][13] The LIF excitation and dispersed fluorescence spectra reported by Fukushima, Mayana and Obi 13 led to the determination of both the electronic transition moment of the…”

“…Most of the SiH 2 detection experiments using lasers 5,6,[11][12][13][14][15][16][17][18][19][20][21] have been performed on the à 1 B 1 (0, 2, 0) ϪX 1 A 1 (0, 0, 0) transition near 580 nm because of favorable Franck-Condon access and of the availability of an excellent dye in the corresponding range ͑Rhodamine 6G͒. Jasinski and coworkers [14][15][16] used frequency modulation and direct absorption techniques to monitor SiH 2 by detecting some rovibronic transitions of this band near 17250 cm Ϫ1 .…”

“…In both singlet states, large excitations of the bending vibration would bring the molecule near a linear configuration, thus enabling a large Renner-Teller interaction, which has been identified from the analysis of rovibronic spectra and lifetimes of excited levels. [4][5][6] A number of spectroscopic studies has been devoted to this transient species. SiH 2 was first identified by Dubois 30 years ago 7,8 by detection of its electronic absorption spectrum in the visible range.…”