Variational Vibrational\nStates of Methanol (12D)

Full-dimensional (12D) vibrational\nstates of the methanol\nmolecule\n(CH<sub>3</sub>OH) have been computed using the GENIUSH-Smolyak approach\nand the potential energy surface from Qu and Bowman (2013). All vibrational\nenergies are converged better than 0.5 cm<sup>–1</sup> with\nrespect to the basis and grid size up to the first overtone of the\nCO stretch, ca. 2000 cm<sup>–1</sup> beyond the zero-point\nvibrational energy. About 70 torsion-vibration states are reported\nand assigned. The computed vibrational energies agree with the available\nexperimental data within less than a few cm<sup>–1</sup> in\nmost cases, which confirms the good accuracy of the potential energy\nsurface. The computations are carried out using curvilinear normal\ncoordinates with the option of path-following coefficients, which\nminimize the coupling of the small- and large-amplitude motions. It\nis important to ensure tight numerical fulfillment of the <i>C</i><sub>3v</sub>(M) molecular symmetry for every geometry\nand coefficient set used to define the curvilinear normal coordinates\nalong the torsional coordinate to obtain a faithful description of\ndegeneracy in this floppy system. The reported values may provide\na computational reference for fundamental spectroscopy, astrochemistry,\nand for the search of the proton-to-electron mass ratio variation\nusing the methanol molecule.