The enthalpy of formation of 2Π CH

The standard enthalpy of formation, Delta(f)H(o), of (2)Pi CH has been determined at converged levels of ab initio electronic structure theory, including high order coupled cluster and full configuration interaction benchmarks. The atomic Gaussian basis sets employed include the (aug)cc-p(C)VXZ family with X = 3,4,5 and 6. Extrapolations to the complete one-particle basis set and the full configuration interaction limits, where appropriate, have been performed to reduce remaining computational errors. Additional improvements in the enthalpy of formation of (2)Pi, CH were achieved by appending the valence-only treatment with core-valence correlation, relativistic effects including spin-orbit correlation, and the diagonal Born-Oppenheimer correction. The recommended values for Delta(f)H(0)(o) and Delta(f)H(298)(o) Of (2)Pi CH are 592.48(-0.56)(+0.47) kJ mol(-1) and 595.93(-0.56)(+0.47) kJ mol(-1), respectively.