Vibrational transition moments of CH4 from first principles

Abstract

A new nine-dimensional (9D), 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 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 .

Self- and air-broadened line shapes in the 2ν3 P and R branches of 12CH4

“…[18] and the references therein), the quantum assignments of many observed features remain unidentified. Efforts to interpret and calculate the positions and intensities for this polyad are ongoing, using both Hamiltonian [16,17] and ab initio formalisms [19,20].…”

Ab initio computational spectroscopy and vibrational dynamics of polyatomic molecules: Applications to syn and anti-CH3CHOO and NO3

“…There has also been substantial progress in achieving this goal for general tetraatomics, see for example Refs. [5][6][7][8] and for some larger, albeit semi-rigid molecules, such as CH 4 [9,10], C 2 H 4 [11,12] and CH 3 OO [13]. There has also been significant progress in developing global, i.e., describing multiple minima and in some cases fragment channels, PESs for tetraatomics, based on strict mathematical fitting of tens of thousands of high-level electronic energies.…”

A fast algorithm for the construction of integrity bases associated to symmetry-adapted polynomial representations: application to tetrahedral $$\mathrm {XY_4}$$ XY 4 molecules

“…They can be generated with only the 9 basic invariants and 132 secondary invariants. Similarly, EDMS for methane of order 6 have already appeared in the literature [50,62]. The 9 basic invariants and 143 F 2 , z-covariant numerator polynomials of degree less or equal to 6 (see Table 6) are enough to generate the 400 linearly independent polynomials required to span the vector space of F 2 , z-covariant polynomials of sixth degree.…”

“…As a matter of fact, various types of such coordinates have appeared in the literature for this system that are amenable to our treatment. We can mention curvilinear internal displacements (bond lengths and interbond angles) [41,42], Cartesian normal coordinates [41,[43][44][45][46][47], symmetrized coordinates based on Morse coordinates on Radau vectors for stretching modes and cosines of valence bond angles for bending modes [8], haversines of bond angles [48], cosines of valence bond angles times functions of bond lengths [49], symmetrized coordinates based on bond lengths, interbond angles and torsion angles [15], or interbond angles and bond lengths times a gaussian exponential factor [50].…”