Variational Vibrational States of Methanol (12D)

Abstract

Full-dimensional (12D) vibrational states of the methanol molecule (CH${}_3$OH) 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 seventy 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 fulfilment of the $C_{3\mathrm{v}}$(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.

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• Strong parity-violation effects induced by large-amplitude motions: A quantum-dynamics study of substituted chiral methanols
• Accurate, full-dimensional computations of thousands of complex vibrational eigenstates with tree tensor network states