A molecular orbital study on H and H-2 elimination pathways from methane, ethane, and propane

Decomposition pathways for propane, as well as methane and ethane for compa rison, in its ground electronic state were studied using density functional and high accuracy ab initio calculations. The reaction pathways were chara cterized by locating the transition states and following the intrinsic reac tion coordinate. Atomic hydrogen as well as molecular hydrogen elimination pathways were investigated, including three deuterated propane species for comparison with experiment. The methyl and ethyl groups in propane are foun d to stabilize transition states and radical/biradical intermediates along the reaction pathways. For propane, 2,2-elimination of an hydrogen molecule is found to be the dominant molecular elimination pathway, in agreement wi th recent photochemical experiments. We find 1,1-elimination to be the next important molecular elimination pathway, followed by 1,2-elimination, whic h disagrees with the experimental result favoring 1,2- over 1,1-elimination . (C) 2000 American Institute of Physics. [S0021-9606(00)31239-9].