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

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.