A global \textit{ab initio} dipole moment surface for methyl chloride

TL;DR

This paper presents a newly developed ab initio dipole moment surface for methyl chloride, enabling accurate spectral calculations that align well with experimental data, and provides a comprehensive rotation-vibration line list.

Contribution

The paper introduces a symmetry-adapted analytic dipole moment surface for methyl chloride at a high level of theory, facilitating precise spectral predictions.

Findings

Good agreement with experimental vibrational transition moments

Accurate line intensities for key vibrational bands

Comprehensive rotation-vibration line list up to J=85

Abstract

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 CH$_3$Cl show good agreement with a range of experimental results. This includes vibrational transition moments, absolute line intensities of the $\nu_1$, $\nu_4$, $\nu_5$ and $3\nu_6$ bands, and a rotation-vibration line list for both CH$_{3}{}^{35}$Cl and CH$_{3}{}^{37}$Cl 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.