Ab initio investigation of the CO–N2 quantum scattering: The collisional perturbation of the pure rotational R(0) line in CO

Abstract

We report fully quantum calculations of the collisional perturbation of a molecular line for a system that is relevant for Earth's atmosphere. We consider the N 2 -perturbed pure rotational R(0) line in CO. The results agree well with the available experimental data. This work constitutes a significant step towards populating the spectroscopic databases with ab initio collisional line-shape parameters for atmosphere-relevant systems. The calculations were performed using three different recently reported potential energy surfaces (PESs). We conclude that all three PESs lead to practically the same values of the pressure broadening coefficients.

Fully quantum calculations of O2–N2 scattering using a new potential energy surface: Collisional perturbations of the oxygen 118 GHz fine structure line

“…38 Similar work is in progress for N 2 -perturbed CO, which is relevant for Earth's atmosphere; recently the first results were published in Ref. 39. This work is in line with those developments, but addresses more challenging systems for which the active molecule is in the triplet spin state.…”

“…( 6) grows considerably with the kinetic energy of the binary collision. 39 In the present case of O 2 ( 3 Σ − g )-N 2 ( 1 Σ + g ) scattering, an additional degree of freedom is introduced into the problem by the non-zero electronic spin S of the ground-state O 2 . The fine-structure splitting in O 2 is small compared with the spacings between the rotational levels, hence molecular oxygen may be accurately described within the Hund's case (b) limit.…”

“…and the sum of these three indices must be an even integer. 39 Expressed in terms of the radial coefficients A LaL b L (R), the potential matrix elements in the close-coupling equations take the form…”

“…13,89 The radial terms of the potential are obtained by integrating Eq. ( 19) over the angular distribution: 39,41…”

“…91 For binary collisions between diatomic molecules typical for Earth's atmosphere, the {|N a m a , |N b m b } basis size used in the calculations grows considerably with E k , the relative kinetic energy of the monomers. 39 To reduce the number of basis elements necessary for the convergence of numerical calculations, we made use of the fact that the non-zero spin of the 14 N nuclei gives rise to the two isomers of molecular nitrogen (ortho-N 2 , for which the total nuclear spin I = 0, 2 and only even N b values occur; and para-N 2 , for which I = 1 and only odd values of N b occur). Thus the scattering calculations are performed independently for the O 2 -ortho-N 2 and O 2para-N 2 systems.…”