State-selective reaction dynamics of atomic oxygen with molecular hydrogen, methanethiol, and ethanethiol

Reaction dynamics have been studied for the following four systems: (1) The rotational state distribution of the nascent NO fragment generated from the photodissociation of (i-C₃H₇) ₃SiONO near 226 nm (S₂ absorption band) has been obtained via 1+1 resonance-enhanced multiphoton ionization (REMPI) spectroscopy and with a time-of-flight mass spectrometer (TOFMS). The absence of vibrational excitation and relative cold rotational distribution suggest a direct dissociation mechanism upon photolysis of the parent molecule. (2) The reaction dynamics of O(3P) and H₂(v = 1). The quantum state specific reactant H₂(v = 1) was prepared effectively via Stimulated Raman Pumping (SRP). The internal quantum state distribution of the product OH (X 2Π_1/2,3/2) was interrogated by laser-induced fluorescence (LIF) spectroscopy. The one-quantum vibrational excitation of hydrogen not only dramatically increases the reaction rate, but also may have slightly changed the reaction mechanism from the known ground-state hydrogen reaction. (3) Experimental and ab initio studies of the reaction dynamics of O(3P) + CH₃SH. Experiments utilized LIF detection of OH, CH₃S, SO, and also HSO. Theoretically, ab initio energy evaluations using Gaussian 94 software and G2MP2 theory, and ab initio molecular dynamics were carried out for the reaction. The combination of the experimental and theoretical works has resulted in great insight into the reaction mechanism. (4) Experimental study of the reaction dynamics of O(3P) + C₂H ₅SH by the similar experimental measurements to the reaction O( 3P) + CH₃SH. The reaction O(3P) + C ₂H₅SD further eliminated the ambiguity in confirming the each other in suggesting the proper reaction mechanisms for the two reaction systems.