Abstract
New nine-dimensional (9D), ab initio electric dipole moment surfaces (DMSs) of methane in its ground electronic state are presented. The DMSs are 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 these 9D DMSs in terms of sixth-order polynomials. Vibrational transition moments as well as band intensities for a large number of IR-active vibrational bands of 12CH4 are computed by vibrationally averaging the ab initio dipole moment components. The vibrational wavefunctions required for these averages are computed variationally using the program TROVE and a new ‘spectroscopic’ 12CH4 potential energy surface. The new DMSs will be used to produce a hot line list for 12CH4.
Highlights
Methane plays an important role in atmospheric and astrophysical chemistry
Its rotationvibration spectrum is of key importance for models of the atmospheres of bodies ranging from Titan to cool stars
In this work we present a new ab initio dipole moment surface (DMS) for CH4 which is used to generate the vibrational transition moments and band intensities of 12CH4 for a large number of vibrationally allowed transitions
Summary
Methane plays an important role in atmospheric and astrophysical chemistry. Its rotationvibration spectrum is of key importance for models of the atmospheres of bodies ranging from Titan to cool stars. The goal of this paper is to bridge this gap and provide an accurate and detailed ab initio DMS of CH4 To this end we employed an explicitly correlated (F12) coupled cluster method in conjunction with an F12-optimized basis set to generate a nine-dimensional (9D) DMS of CH4. This surface is used to compute vibrational transition moments and vibrational band intensities of 12CH4 for a large number of IR-active transitions in the range between 0 and 10000 cm−1.
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