TIME-RESOLVED STUDY OF THE TRANSIENTS PRODUCED IN THE CO2 AND ARF LASER FLASH-PHOTOLYSIS OF GASEOUS SILACYCLOBUTANE AND 1,3-DISILACYCLOBUTANE

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 i ts optical absorption spectrum, with lambda(max) approximate to 260 nm . Under conditions of low laser fluence, this species has two decay ch annels: a unimolecular process (k = 2.3 +/- 0.7 x 10(4) s(-1)) and a r eaction with the parent compound (k(SCB) = 2.0 +/- 0.3 x 10(-13) cm(3) molecule(-1) s(-1) and k(DSCB) = 3.0 +/- 0.5 x 10(-13) cm(3) molecule (-1) s(-1)). At high fluence (7.2 J cm(-2) for the CO2 laser and 6 J c m(-2) for the ArF laser), the transient absorption signals become very complex owing to the onset of a number of other reactions and the for mation of several additional transient species which appear to have st rong absorption in the 250-650 nm region, with peaks/shoulders at ca. 260, 320 and 435 nm but these could not be identified unambiguously.