High-AccuracyCO2Line Intensities Determined from Theory and Experiment

Abstract

Atmospheric CO 2 concentrations are being closely monitored by remote sensing experiments which rely on knowing line intensities with an uncertainty of 0.5% or better. Most available laboratory measurements have uncertainties much larger than this. We report a joint experimental and theoretical study providing rotation-vibration line intensities with the required accuracy. The ab initio calculations are extendible to all atmospherically important bands of CO 2 and to its isotologues. As such, they will form the basis for detailed CO 2 spectroscopic line lists for future studies.

Improved potential energy surface and spectral assignments for ammonia in the near-infrared region

“…For this DMS, dipole moment components μ A were calculated using the finite field procedure with an external field value of ±5 × 10 −5 a.u. For both water [49] and carbon dioxide [50] we have demonstrated that even though the finite field method requires seven times more computations than using expectation values, the resulting DMS is more accurate. Calculations were performed using internally contracted MRCI in the full valence reference space comprising 8 electrons in 7 orbitals, with the aug-cc-pwCVQZ basis set.…”

Uncertainty estimates for theoretical atomic and molecular data

“…This is done, at least in part, to aid the predictions of the rotational spectrum of these species and hence their detection in the laboratory and space [181,182]. One area where uncertainty assessment is beginning to have significant impact is the computation of dipole-moment surfaces [59,60] and hence rotation-vibration transition intensities [184]. The methodology used here is based on adapting the FPA method for computing the dipole moment surface (DMS) and then performing multiple computations using different PESs and DMSs to establish stability of the results [185,186].…”

Quantification of uncertainties in OCO-2 measurements of XCO<sub>2</sub>: simulations and linear error analysis

“…The values used by the OCO-2 algorithm are based on Devi et al (2007Devi et al ( , 2016. Values from Polyansky et al (2015) differ from those in Devi et al (2016) by ∼ 1.2 %.…”