Variational Vibrational States of Methanol (12D).

Area of Science:

• * Quantum chemistry
• * Molecular spectroscopy
• * Astrochemistry

Background:

• * Methanol (CH3OH) is a key molecule in astrochemistry and a benchmark for theoretical studies.
• * Accurate computation of its vibrational states is crucial for interpreting experimental data and exploring fundamental physics.
• * Previous studies have been limited in dimensionality or accuracy.

Purpose of the Study:

• * To compute full-dimensional (12D) vibrational states of methanol.
• * To provide highly accurate vibrational energies for comparison with experimental data.
• * To establish a computational reference for spectroscopy, astrochemistry, and proton-to-electron mass ratio variation studies.

Main Methods:

• * Employed the GENIUSH-Smolyak approach for full-dimensional vibrational state computations.
• * Utilized the high-accuracy potential energy surface from Qu and Bowman (2013).
• * Incorporated curvilinear normal coordinates with path-following coefficients to manage coupled motions and ensure C3v(M) symmetry.

Main Results:

• * Calculated vibrational energies converged to better than 0.5 cm⁻¹.
• * Reported and assigned approximately 70 torsion-vibration states.
• * Achieved excellent agreement (< few cm⁻¹) between computed and experimental vibrational energies.

Conclusions:

• * The study demonstrates the accuracy of the GENIUSH-Smolyak approach and the Qu-Bowman potential energy surface for methanol.
• * The computed vibrational states serve as a reliable reference for various scientific applications.
• * This work advances the understanding of molecular vibrations in floppy systems like methanol.