Bend Excitation Is Predicted to Greatly Accelerate Isomerization of trans-Hydroxymethylene to Formaldehyde in the Deep Tunneling Region.

Using a new potential energy surface, based on fitting around 33,000 CCSD(T)-F12/aug-cc-pVTZ energies, a robust set of predictions is made for mode-specific isomerization of trans-hydroxymethylene to formaldehyde in the deep tunneling region. The calculations make use of a recent projection model for mode-specific tunneling based on the rectilinear Q(im) path [ Wang , Y. ; Bowman , J. M. J. Chem. Phys. 2013 , 139 , 154303 ]. The most interesting prediction is a large decrease in the half-life from roughly 5 h for the ground vibrational state to roughly 1.5 min and 1 s by excitation of the fundamental and first overtone of the asymmetric bending normal mode, respectively. The properties of the new PES are described along with variational calculations of low-lying vibrational states of trans- and cis-hydroxymethylene.