Time-resolved study of the transients produced in the CO₂ and ArF laser flash photolysis of gaseous silacyclobutane and 1,3-disilacyclobutane

Abstract

A time-resolved study of the transients produced in the TEA CO₂ or ArF laser-induced decomposition of gaseous silacyclobutane (SCB) and 1,3-disilacyclobutane (DSCB) is reported. Both compounds produce transient H₂C=SiH₂ as the major primary product, which has been identified by its optical absorption spectrum, with λ _max≈ 260 nm. Under conditions of low laser fluence, this species has two decay channels: a unimolecular process (k= 2.3 ± 0.7 × 10⁴ s^-1) and a reaction with the parent compound (k_SCB= 2.0 ± 0.3 × 10^-13 cm³ molecule^-1 s^-1 and k_DSCB= 3.0 ± 0.5 × 10^-13 cm³ molecule^-1 s^-1). At high fluence (7.2 J cm^-2 for the CO₂ laser and 6 J cm^-2 for the ArF laser), the transient absorption signals become very complex owing to the onset of a number of other reactions and the formation of several additional transient species which appear to have strong absorption in the 250-650 nm region, with peaks/shoulders at ca. 260, 320 and 435 nm but these could not be identified unambiguously.