A global ab initio dipole moment surface for methyl chloride

- New high-level ab initio dipole moment surface for methyl chloride.
- Rigorously tested against a range of experimental results.
- Computed absolute line intensities comparable with highly accurate experimental measurements for certain fundamental bands.
- Missing band identified in HITRAN.
- DMS performs well for weaker bands.

A new dipole moment surface (DMS) for methyl chloride has been generated at the CCSD(T)/aug-cc-pVQZ(+d for Cl) level of theory. To represent the DMS, a symmetry-adapted analytic representation in terms of nine vibrational coordinates has been developed and implemented. Variational calculations of the infrared spectrum of CH3Cl show good agreement with a range of experimental results. This includes vibrational transition moments, absolute line intensities of the ν1, ν4, ν5 and 3ν6 bands, and a rotation-vibration line list for both CH335Cl and CH337Cl including states up to J=85 and vibrational band origins up to 4400 cm−1. Across the spectrum band shape and structure are well reproduced and computed absolute line intensities are comparable with highly accurate experimental measurements for certain fundamental bands. We thus recommend the DMS for future use.