Abstract
A high-level quartic ab initio potential energy surface of methanol has been used to calculate spectroscopic constants of the 12CH3OH molecule. These include coefficients of quartic anharmonic resonance terms, Darling-Dennison constants, for stretching states. A model expressed in terms of dimensionless normal coordinates has been employed in the calculation of O—H and C—H stretching vibrational states in high-overtone regions. Both cubic Fermi and quartic Darling-Dennison anharmonic coupling terms have been included in the model in order to take into account strong resonances between different states. The nonlinear least-squares method has been used to optimize some of the model parameters employing experimental term values of 12CH3OH as data. Vibrational assignments are suggested for the first C—H stretching overtone region.