Theoretical Enthalpies of Formation of CH m Cl n : Neutral Molecules and Cations

Ab initio molecular orbital calculations have been performed on all possible neutral molecules and cations of the type CHmCln (m + n = 1−3). Equilibrium structures were optimized using gradient techniques at HF/6-31G(d,p), MP2/6-311G(d,p), QCISD/6-311G(d,p), and MP2/6-311++G(d,p). Thermochemical properties (standard enthalpies of formation, adiabatic ionization energies, and proton affinities) have been calculated at QCISD(T)/6-311++G(3df,3pd)//MP2/6-311++G(d,p) and QCISD(T)/6-311G(2df,p)//QCISD/6-311G(d,p), both including core-electron correlation, and at MP4SDTQ/6-311G(2df,p)//MP2/6-311G(d,p), frozen core. Calculations at the first level of theory are accurate to ±1.0 kcal mol-1, and at the second and third levels of theory, to ±2.3 kcal mol-1. Recent experimental data are critically reviewed against these calculated results, and theory indicates that some experimental values are incorrect. Calculated QCISD(T)/6-311++G(3df,3pd) values for the enthalpies of formation for CCl+ and CHCl+ are 304.9 and 286....