Active Thermochemical Tables: The Partition Function of Hydroxymethyl (CH 2 OH) Revisited
The best currently available set of temperature-dependent non-rigid rotor anharmonic oscillator (NRRAO) thermochemical and thermophysical properties of hydroxymethyl radical is presented. The underlying partition function relies on a critically evaluated complement of accurate experimental and theoretical data, and is constructed using a two-pronged strategy that combines contributions from large amplitude motions obtained from direct counts, with contributions from the other internal modes of motion obtained from analytic NRRAO expressions. The contributions from the two strongly coupled large-amplitude motions of CH 2 OH, OH torsion and CH 2 wag, are based on energy levels obtained by solving the appropriate two-dimensional projection of a fully-dimensional potential energy surface that was recently obtained at the CCSD(T)/cc-pVTZ level of theory. The contributions of the remaining seven, more rigid, vibrational modes and of the external rotations are captured by NRRAO corrections to the standard rigid rotor harmonic oscillator (RRHO) treatment, which include corrections for vibrational anharmonicities, rotation-vibration interaction, Coriolis effects, and low-temperature. Here, the basic spectroscopic constants needed for the construction of the initial RRHO partition function rely on experimental ground-state rotational constants and the best available experimental fundamentals, additionally complemented by fundamentals obtained from the variational solution of the full-dimensional potential energy surface using a recently developed two-component multi-layer Lanczos algorithm.