Kinetic studies of atmospherically relevant silicon chemistry Part I: Silicon atom reactions

Atomic silicon is generated by meteoric ablation in the Earth's upper atmosphere (70-110 km). The reactions of Si(P-3(J)) atoms with several atmospherically relevant species were studied by the pulsed laser photolysis of a Si atom precursor ( typically PheSiH(3)), followed by time-resolved laser induced fluorescence at 251.43 nm (Si(3p(2) P-3(0) -> 4s P-3(1))). This yielded: k(Si + O-2, 190-500 K) = 9.49 x 10(-11) + 1.80 x 10(-10) x exp(-T/115 K) cm(3) molecule(-1) s(-1) (uncertainty <= +/- 15%), in good accord with recent high-level theoretical calculations but in marked disagreement with previous experimental work; k(Si + O-3, 190-293 K) = (4.0 +/- 0.5) x 10(-10) cm(3) molecule(-1) s(-1); k(Si + CO2, 293 K) <= 1.2 x 10(-14) cm(3) molecule(-1) s(-1); and k(Si + H2O, 293 K) <= 2.6 x 10(-13) cm(3) molecule(-1) s(-1). These results are explained using a combination of quantum chemistry calculations and long-range capture theory. The quenching rate coefficients k(Si(D-1(2)) + N-2, 293 K) = (4.0 +/- 0.7) x 10(-11) cm(3) molecule(-1) s(-1) and k(Si(D-1(2)) + H2O, 293 K) = (2.3 +/- 0.3) x 10(-10) cm(3) molecule(-1) s(-1) were also determined.