Vibrational transition moments of CH${}_4$ from first principles

Abstract

A new nine-dimensional (9D), \textit{ab initio} electric dipole moment surface (DMS) of methane in its ground electronic state is presented. The DMS is computed using an explicitly correlated coupled cluster CCSD(T)-F12 method in conjunction with an F12-optimized correlation consistent basis set of the TZ-family. A symmetrized molecular bond representation is used to parameterise the 9D DMS in terms of sixth-order polynomials. Vibrational transition moments as well as band intensities for a large number of IR-active vibrational bands of ${}^{12}$CH${}_4$ are computed by vibrationally averaging the \textit{ab initio} dipole moment components. The vibrational wavefunctions required for these averages are computed variationally using the program TROVE and a new `spectroscopic' ${}^{12}$CH${}_4$ potential energy surface. The new DMS will be used to produce a hot line list for ${}^{12}$CH${}_4$.

J. Molec. Spectrosc. (submitted)

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