KINETIC-STUDIES OF THE REACTIONS OF ATOMIC CHLORINE AND BROMINE WITH SILANE

The kinetics of the reactions Cl(2P(J)) + SiH4 (1) and Br(2P(J)) + SiH4 (2) have been investigated by time-resolved atomic resonance fluorescence spectroscopy. Halogen atoms were generated by flash photolysis of CCl4 and CH2Br2. Experiments over 295-472 K yielded k1 = (1.56 +/- 0.11) x 10(-10) exp[(2.0 +/- 0.2) kJ mol-1/RT] cm3 s-1 and studies over 295-575 K yielded k2 = (9.0 +/- 1.5) x 10(-11) exp[(-17.0 +/- 0.6) kJ mol-1/RT] cm3 s-1. 95% confidence intervals are about +/- 10% and +/- 20%, respectively. These expressions are in good agreement with most earlier measurements. An expression for k-1 is also derived. Alternative interpretations of the negative activation energy for k1, based on transition-state theory or formation of an intermediate adduct, are discussed.