ExoMol line lists – XXXIX. Ro-vibrational molecular line list for CO2

Abstract

A new hot line list for the main isotopologue of CO2, 12C16O2 is presented. The line list consists of almost 2.5 billion transitions between 3.5 million rotation-vibration states of CO2 in its ground electronic state, covering the wavenumber range 0–20 000 cm−1 (λ > 0.5 µm) with the upper and lower energy thresholds of 36 000 cm−1 and 16 000 cm−1, respectively. The ro-vibrational energies and wavefunctions are computed variationally using the accurate empirical potential energy surface Ames-2. The ro-vibrational transition probabilities in the form of Einstein coefficients are computed using an accurate ab initio dipole moment surface with variational program TROVE. A new implementation of TROVE which uses an exact nuclear-motion kinetic energy operator is employed. Comparisons with the existing hot line lists are presented. The line list should be useful for atmospheric retrievals of exoplanets and cool stars. The UCL-4000 line list is available from the CDS and ExoMol data bases.

The 2020 release of the ExoMol database: Molecular line lists for exoplanet and other hot atmospheres

“…A new ExoMol line list UCL-40 0 0 for CO 2 has been produced [132] using an accurate ab initio dipole moment surface (DMS) by Polyansky et al [208] and empirical potential energy surface (PES) Ames-2016 by Huang et al [209] ; where possible computed energies have been replaced by empirical ones derived from HI-TRAN. The UCL-40 0 0 line list covers the wavenumber range 0-20 0 0 0 cm −1 and should be applicable for temperatures up to 40 0 0 K [132] . It is recommended for use in high temperature applications.…”

“…To date the new standard of the States file has being applied to only a number of key/recent line lists namely H 2 O (POKAZATEL) [61] , AlH (AlHambra) [122] , C 2 (8states) [124,194] , HCCH (aCeTY) [130] , CO 2 (UCL-40 0 0) [132] , H 3 O + (eXeL) [133] and TiO (Toto) [126] . A rolling programme is in place for updating the other files so the uncertainty is uniformly available for all sources.…”

Treating linear molecules in calculations of rotation-vibration spectra

“…( 39) (which are not orthogonal for this weight factor) and then ortho-normalized using one of the standard techniques, such as Gram-Schmidt's orthonormalization given in Eqs. ( 36)- (38). The correct weight sin l+1/2 (ρ) makes these polynomials compatible with the integrals from Eqs.…”

“…4, where PES by Huang et al 37 was used. The details of the TROVE calculations can be found in the work of Yurchenko et al 38…”

Artificial Symmetries for Calculating Vibrational Energies of Linear Molecules

“…The theory and programming work reported in Ref. [19] and in the present work have already been employed for generating hot molecular line lists for SiO 2 [45] and CO 2 [46] as well as to produce a quadrupole spectrum of H 2 O [47]. TROVE uses an automatic approach for constructing a symmetry-adapted basis set to be used in setting up a matrix representation of the molecular rotation-vibration Hamiltonian [48] In order to compute the vibrational energies for a linear molecule, we solve the Schrödinger equation for the HamiltonianĤ (0) vib,lin , which involves the bending and stretching motions and, as explained in Introduction, the rotational motion about the a axis.…”