ExoMol molecular line lists – XIV. The rotation–vibration spectrum of hot SO₂

Abstract

Sulphur dioxide is well-known in the atmospheres of planets and satellites, where its presence is often associated with volcanism, and in circumstellar envelopes of young and evolved stars as well as the interstellar medium. This work presents a line list of 1.3 billion 32 S 16 O 2 vibration-rotation transitions computed using an empirically-adjusted potential energy surface and an ab initio dipole moment surface. The list gives complete coverage up to 8000 cm −1 (wavelengths longer than 1.25 µm) for temperatures below 2000 K. Infrared absorption cross sections are recorded at 300 and 500 C are used to validated the resulting ExoAmes line list. The line list is made available in electronic form as supplementary data to this article and at www.exomol.com.

The ExoMol project: Software for computing large molecular line lists

“…Algorithmic improvements include the following: The automated Gauss‐(associated) Legendre quadrature generation procedure, which was adapted from one given by Stroud and Secrest has been replaced by a brute force one which involves finding zeros in the polynomial equation for the N point quadrature. This was found to be essential for grids with and has been successfully used for N up to 150 . The automatic check on the validity of grid obtained by comparing summed weights with the analytic value given by Stroud and Secrest has been retained. For large calculations, module ROTLEV3 b in the published version of DVR3D can spend a long time constructing the final Hamiltonian matrix.…”

“…Hot line list can involve calculations with high J and experience has shown that in this case not all ( J , k ) combinations are actually needed. An option has been implemented where unneeded high k calculations are not performed . In practice, this does not save much computer time, since the initial ( J , k ) calculations are quick, but does save disk space. Again for large calculations, the algorithm used by module DIPOLE3 to read in the wave functions required a lot of redundant reads.…”

“…In practice, this does not save much computer time, since the initial ( J , k ) calculations are quick, but does save disk space. Again for large calculations, the algorithm used by module DIPOLE3 to read in the wave functions required a lot of redundant reads. DIPOLE3 has been restructured to reduce the number of times the wave functions need to be read …”

“…This in turn requires larger basis sets and therefore larger Hamiltonian matrices, which associated increase of the calculation costs in terms of memory (both RAM and storage) and time. For example, for the SO 3 line list with extremely high rotational excitations (up to J = 130) due to the heavy character of the molecule, the size of the Hamiltonian matrices to be solved has to be as large as 400,000 × 400,000, which represents our biggest calculation so far. This is despite the fact that only the smallest matrix ( and symmetries of (M)) had to be considered due to the nuclear spin statistics of 32 S 16 O 3 .…”

Perspective: Accurate ro-vibrational calculations on small molecules

“…49 This has led to the computation of extensive line list of transitions for hot molecules by a number of groups. 19,[50][51][52][53][54][55] Recent work has particularly focussed on providing line lists for hot methane, 51,[56][57][58] the use of which has also been shown to have a dramatic effect on models of astronomical objects, 43 see Fig. 1.…”