Theoretical Studies of the O(3P) + Methane Reaction

The dynamics of the O( 3 P) + CH 4 reaction has been studied using the quasiclassical trajectory method in conjunction with direct dynamics electronic structure calculations. Several electronic structure methods were used, including DFT (B3LYP/6-31G*) and semiempirical (PM3 and MSINDO) methods. In addition, a recently developed analytical surface (PES) was considered. Our calculations have emphasized collision energies of 1−5 eV because of the importance of this energy range in low Earth orbit research. Our calculated cross sections show that at high energies the H elimination channel yielding H + OCH 3 is favored over the lowest barrier product (OH + CH 3 ). Analysis of product energy disposal shows OH and CH 3 products that are fairly cold, with most of the energy released to translation. On the other hand, OCH 3 carries away most of the energy released to the H + OCH 3 products. Angular distributions for OH + CH 3 are mainly forward scattered, with a shift from sideways to forward as energy is increased. H + OCH 3 is predominantly backward scattered (i.e., the H atom scatters forward). Opacity functions reveal a high selectivity toward OH + CH 3 for high impact parameters whereas the H + OCH 3 channel is dominant at low impact parameters. MSINDO results compare quite well with more accurate B3LYP/6-31G* calculations, noticeably improving over PM3 for most of the dynamics properties studied.