Ab initio study of the CD4 + Cl ⇄ CD3 + DCl equilibrium. Thermochemistry of the CD3 radical

The equilibrium reaction of CD4 + Cl ⇄ CD3 + DCl has been studied by ab initio methods. Kinetic parameters of the reaction were calculated at the MP2(fc)/cc-pVQZ//MP2(fc)/cc-pVQZ level of theory in conjunction with the thermodynamic transition state theory. The Arrhenius expression obtained for the forward reaction is k(CD4 + Cl) = 1.16 × 10−11exp(−16.54 kJ mol−1/RT) cm3 molecule−1 s−1 (Arrhenius parameters were calculated for T = 298 K). The rate constants of the forward reaction were combined with the experimentally measured rate constants of the reverse reaction for thermodynamic studies. A third-law determination for the CD3 radical heat of formation yielded a value of 139.6 ± 2.9 kJ mol−1 and a second-law determination a value of 139.2 ± 2.5 kJ mol−1 at 298 K after a heat capacity correction. A mean value from these determinations, 139.4 mol−1, was used as the reference value in the calculations of thermodynamic properties of the CD3 radical by statistical thermodynamic methods over the temperature range, 100-1500 K.