Modeling the electron-impact dissociation of methane

作者：Ziolkowski Marcin; Vikar Anna; Mayes Maricris Lodriguito; Bencsura Akos; Lendvay Gyoergy; Schatz George C^*

来源：Journal of Chemical Physics, 2012, 137(22): 22A510.

DOI：10.1063/1.4733706

The product yield of the electron-impact dissociation of methane has been studied with a combination of three theoretical methods: R-matrix theory to determine the electronically inelastic collisional excitation cross sections, high-level electronic structure methods to determine excited states energies and derivative couplings, and trajectory surface hopping (TSH) calculations to determine branching in the dissociation of the methane excited states to give CH3, CH2, and CH. The calculations involve the lowest 24 excited-state potential surfaces of methane, up to the ionization energy. According to the R-matrix calculations, electron impact preferentially produces triplet excited states, especially for electron kinetic energies close to the dissociation threshold. The potential surfaces of excited states are characterized by numerous avoided and real crossings such that the TSH calculations show rapid cascading down to the lowest excited singlet or triplet states, and then slower the dissociation of these lowest states. Product branching for electron-impact dissociation was therefore estimated by combining the electron-impact excitation cross sections with TSH product branching ratios that were obtained from the lowest singlet and triplet states, with the singlet dissociation giving a comparable formation of CH2 and CH3 while triplet dissociation gives CH3 exclusively. The overall branching in electron-impact dissociation is dominated by CH3 over CH2. A small branching yield for CH is also predicted.

• 出版日期2012-12-14
• 单位西北大学