An ab initio variationally computed room-temperature line list for 32S16O3

Abstract

Ab initio potential energy and dipole moment surfaces are computed for sulfur trioxide (SO3) at the CCSD(T)-F12b level of theory with appropriate triple-zeta basis sets. The analytical representations of these surfaces are used, with a slight correction, to compute pure rotational and rotation-vibration spectra of (32)S(16)O3 using the variational nuclear motion program TROVE. The calculations considered transitions in the region 0-4000 cm(-1) with rotational states up to J = 85. The resulting line list of 174,674,257 transitions is appropriate for modelling room temperature (32)S(16)O3 spectra. Good agreement is found with the observed infrared absorption spectra and the calculations are used to place the measured relative intensities on an absolute scale. A list of 10,878 experimental transitions is provided in a form suitable for inclusion in standard atmospheric and planetary spectroscopic databases.

ExoMol molecular line lists – XVII. The rotation–vibration spectrum of hot SO3

“…Here ri is a bond length and αij is an interbond bond angle. Further details of this functional form and symmetry relations between ∆f ijk... can be found elsewhere (Yurchenko et al 2005b;Underwood et al 2013). The refined potential coefficients ∆f ijk... were determined using a least squares fitting algorithm which uses the derivatives of energies with respect to ∆f ijk... computed via the Hellmann-Feynman theorem (Feynman 1939).…”

“…Here the KE expansion order was increased to 6 th in order to allow better convergence. For the detailed description of the basis set see Underwood et al (2013). Here it suffices to define the maximal polyad number Pmax used in TROVE to control the size of the basis set.…”

“…As for the experimental studies for SO3, none of this work provided transition intensities. Our preliminary study for this project (Underwood et al 2013), which produced the ab initio, room-temperature UYT line list, therefore provides the first absolute transition intensities for SO3. These were used in the 2012 release of the HITRAN database (Rothman et al 2013) to scale the relative experimental measurements allowing SO3 to be included in the database for the first time.…”

Accurate ab initio vibrational energies of methyl chloride

“…The flexibility of TROVE has allowed a range of molecular systems to be treated, 49,52,83,[89][90][91][92][93][94][95][96] and for the present study, the functionality has been extended to handle molecules of the form XY 3 Z.…”

A global ab initio dipole moment surface for methyl chloride

“…The cyclic permutation operation (123) replaces nucleus 1 with nucleus 2, nucleus 2 with nucleus 3, and nucleus 3 with nucleus 1; the permutation-inversion operation (12) * interchanges nuclei 1 and 2 and inverts all particles (including electrons) in the molecular centre of mass; the identity operation E leaves the molecule unchanged. The symmetrized molecular bond (SMB) representation has been successfully applied to molecules of C 3v (M) symmetry [66,67] and this approach is employed for the present study.…”