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CO2 and CO are listed as molecules 2 and 5, respectively, in the HITRAN database, with the former being the most important greenhouse gas in the Earth’s atmosphere and the latter being the second most common molecule in the Universe after H2. Thus knowing the line intensities of both CO2 and CO with low uncertainty has wideranging scientific importance. Until recently only the effective Hamiltonian and Dipole Moment Surfaces(DMS) were used to calculate line positions and intensities of these molecules. However, there is a theoretical line list based on variational calculations using a fitted potential energy surface (PES) and an ab initio DMS which has been determined recently1 and which givesCO2 line intensities that are accurate to within a few percent. In this work we attempt to improve and experimentally validate the accuracy of the predicted CO2 line intensities at the sub-percent level. However, only a few lines belonging to four CO2 bands have thus far been measured at this level of uncertainty. We performed ab initio calculations of the PES and DMS of CO2 at the all-electron MRCI level of theory using MOLPRO and an aug-cc-pcQz basis set. Values for about 2000 geometries were calculated with energies up to 20 000 cm−1 above the minimum. We fitted an analytical surface to these DMS points and calculated intensities using the excellent PES of Ref. 1 and our DMS using the variational triatomic nuclear motion program DVR3D2.We will present a comparison of our calculated line intensities with several measured lines in the four above-mentioned bands. This comparison between theory and experiments demonstrates that sub-percent relative uncertainty in the predicted intensities of CO2 lines has been achieved. The results of similarly accurate calculations on CO will also be presented.

Recommendations of an IUPAC Task Group, formed in 2011 on “Intensities and line shapes in high-resolution spectra of water isotopologues from experiment and theory”(Project No. 2011-022-2-100), on line profiles of isolated high-resolution rotational-vibrational transitions perturbed by neutral gas-phase molecules are presented. The well-documented inadequacies of the Voigt profile, used almost universally by databases and radiative-transfer codes to represent pressure effects and Doppler broadening in isolated vibrational-rotational and pure rotational transitions of the water molecule, have resulted in the development of a variety of alternative line profile models. These models capture more of the physics of the influence of pressure on line shapes but, in general, at the price of greater complexity. The Task Group recommends that the partially-Correlated quadratic-Speed-Dependent Hard-Collision profile should be adopted as the appropriate model for high-resolution spectroscopy. For simplicity this should be called the Hartmann–Tran profile (HTP). This profile is sophisticated enough to capture the various collisional contributions to the isolated line shape, can be computed in a straightforward and rapid manner, and reduces to simpler profiles, including the Voigt profile, under certain simplifying assumptions. For further details see: J. Tennyson et al, Pure Appl. Chem., 2014, in press.

High-temperature water linelists for three water isotopologues -H216O,H217O and H218O are calculated using the newly developed potential energy surfaces (PESs) and the high-quality dipole moment surface (DMS)1. ForH216O, a PES accurate up to 40 000 cm−1 was developed and the energy levels cutoff up to 40 000 cm−1 was used. The lines for all the levels up to J =72 are computed.The accuracy of the PES is an order of magnitude better than the one used for the BT2 linelist2.For the two minor isotopologues, less extensive linelists are calculated, which coincide in highest J ≤ 50 and energy levels up to 30 000 cm−1, with the parameters used for the BT2 linelist. A newly-developed method for calculating the PES of isotopologues is used which gives the same level of accuracy for H217O and H218O as obtained for known levels of H216O even when these levels are yet unknown experimentally for the minor isotopologue.