Variational calculations of rovibrational energies of CH4 and isotopomers in full dimensionality using an ab initio potential

We report variational calculations of vibrational energies of ${\mathrm{CH}}_{\mathrm{4}},$ ${\mathrm{CH}}_{\mathrm{3}}\mathrm{D},$ ${\mathrm{CH}}_{\mathrm{2}}{\mathrm{D}}_{\mathrm{2}},$ ${\mathrm{CHD}}_{\mathrm{3}},$ and ${\mathrm{CD}}_{\mathrm{4}},$ using a new version of “Multimode” and a high quality ab initio quartic force field of Lee and co-workers [T. J. Lee, J. M. L. Martin, and P. R. Taylor, J. Chem. Phys. 102, 254 (1995)]. Convergence of the vibrational energies with respect to several numerical aspects of the calculation is examined. The converged vibrational energies are compared with experiment and with previous perturbation theory calculations. Fermi resonance analyses of the fundamentals are presented for all isotopomers. Rovibrational calculations are also reported for ${\mathrm{CH}}_{\mathrm{4}}$ and compared with experiment.