Variational Vibrational States of Methanol (12D)

Full-dimensional (12D) vibrational
states of the methanol
molecule
(CH3OH) have been computed using the GENIUSH-Smolyak approach
and the potential energy surface from Qu and Bowman (2013). All vibrational
energies are converged better than 0.5 cm–1 with
respect to the basis and grid size up to the first overtone of the
CO stretch, ca. 2000 cm–1 beyond the zero-point
vibrational energy. About 70 torsion-vibration states are reported
and assigned. The computed vibrational energies agree with the available
experimental data within less than a few cm–1 in
most cases, which confirms the good accuracy of the potential energy
surface. The computations are carried out using curvilinear normal
coordinates with the option of path-following coefficients, which
minimize the coupling of the small- and large-amplitude motions. It
is important to ensure tight numerical fulfillment of the C3v(M) molecular symmetry for every geometry
and coefficient set used to define the curvilinear normal coordinates
along the torsional coordinate to obtain a faithful description of
degeneracy in this floppy system. The reported values may provide
a computational reference for fundamental spectroscopy, astrochemistry,
and for the search of the proton-to-electron mass ratio variation
using the methanol molecule.