Ab initio study on carbon Kinetic Isotope Effect (KIE) in the reaction of CH4+Cl center dot

Recent studies suggest that the destruction of methane by Cl . in the marine boundary layer could be accounted for as another major sink besides the methane destruction by OH .. High level ab initio molecular orbital calculations have been carried out to study the CH4 + Cl . reaction, the carbon Kinetic Isotope Effect (KIE) is calculated using Conventional Transition-State Theory (CTST) plus Wigner and Eckart semiclassical tunneling corrections. The calculated KIE is around 1.026 at 300 K and has a small temperature variation. This is by far the largest KIE among different processes involving atmospheric methane destruction (e.g., OH ., soil). A calculated mass balance of atmospheric methane including the KIE for the CH4 + Cl . reaction is found to favor those methane budgets with enhanced biological methane sources, which have relatively lighter carbon isotope composition.