Variational Vibrational States of Methanol (12D).

Full-dimensional (12D) vibrational states of the methanol molecule (CHOH) 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 with respect to the basis and grid size up to the first overtone of the CO stretch, ca. 2000 cm 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 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 (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.