The dynamics of formation of HCl products from the reaction of Cl atoms with methanol, ethanol, and dimethyl ether

Abstract

The dynamics of ground state Cl(2P3/2) atom reactions with methanol, methanol-d1, ethanol, and dimethyl ether have been studied both experimentally and theoretically. The reactions were photoinitiated by 355 nm photolysis of Cl2 to produce monoenergetic Cl(2P3/2) atoms that react with ground electronic state organic molecules under single collision conditions. The rotational quantum state population distributions of the nascent HCl(ν′) products were probed by 2+1 resonance-enhanced multiphoton ionization in a time-of-flight mass spectrometer. Nascent HCl(ν′=0) products from reaction of Cl atoms with methanol, methanol-d1 (CH3OD), ethanol, and dimethyl ether, at mean collision energies in the range of 5.6–6.7 kcal/mol, exhibit distributions of population over rotational levels that all peak at J′=3–5. The average rotational energies of the HCl(ν′=0) products for the respective reactions are 〈Erot〉=330±29, 300±24, 340±24, and 256±17 cm−1 (1σ uncertainties). Ab initio calculations were performed in order to examine the mechanisms of Cl atom abstraction of hydrogen from the alcohols and ether. Optimized geometrical structures and vibrational frequencies of molecular complexes and transition states on the reaction pathways were obtained at the MP2/6-311G(d,p) level and their energies were further refined at the G2 level of theory. Comparisons are drawn between the mechanisms and energetic pathways of the various reactions. The degree of rotational excitation of the HCl, which is significantly greater than for Cl atom abstraction of an H atom from alkanes, is attributed to a dipole–dipole interaction between the HCl and RCHOR′ (R, R′=H or CH3) moieties in the products’ region of the potential energy surface.