Elastic scattering and rotational excitation of nitrogen molecules by sodium atoms

Jérôme Loreau,Alexander Dalgarno,Peng Zhang

doi:10.1063/1.3653983

Jérôme Loreau, Alexander Dalgarno + Show 1 more

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https://doi.org/10.1063/1.3653983

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Abstract

A quantal study of the rotational excitation of nitrogen molecules by sodium atoms is carried out. We present the two-dimensional potential energy surface of the NaN(2) complex, with the N(2) molecule treated as a rigid rotor. The interaction potential is computed using the spin unrestricted coupled-cluster method with single, double, and perturbative triple excitations (UCCSD(T)). The long-range part of the potential is constructed from the dynamic electric dipole polarizabilities of Na and N(2). The total, differential, and momentum transfer cross sections for rotationally elastic and inelastic transitions are calculated using the close-coupling approach for energies between 5 cm(-1) and 1500 cm(-1). The collisional and momentum transfer rate coefficients are calculated for temperatures between 100 K and 300 K, corresponding to the conditions under which Na-N(2) collisions occur in the mesosphere.

Highlights

Collisions between sodium atoms and nitrogen molecules occurring in Earth’s mesosphere play an important role in the understanding and development of sodium Laser Guide Stars (LGS).1 LGS are currently being developed at ground-based telescopes in an effort to improve the use of adaptive optics
We have shown that the inelastic transitions contribute to a large part of the momentum transfer cross section for j = 1, and that the inelastic cross sections decrease very quickly with increasing initial rotational level
We have obtained the two-dimensional potential energy surface (PES) of the ground state of the Na–N2 complex by means of the coupled cluster method implemented in MOLPRO with the N–N internuclear distance fixed to its equilibrium geometry

Summary

INTRODUCTION

Collisions between sodium atoms and nitrogen molecules occurring in Earth’s mesosphere play an important role in the understanding and development of sodium Laser Guide Stars (LGS). LGS are currently being developed at ground-based telescopes in an effort to improve the use of adaptive optics. LGS are currently being developed at ground-based telescopes in an effort to improve the use of adaptive optics This technique requires a reference source (a guide star) in order to efficiently correct the effects of the atmospheric distortion on the light received by telescopes. Sodium laser guide stars provide a solution to this problem by shining a laser at a wavelength of 589 nm into the atmosphere This laser light is absorbed by sodium atoms present in the atmosphere and reemitted, providing an artificial star that can be used as a reference star in any region of the sky. The process takes advantage of the natural sodium layer present in the mesosphere at an altitude of about 90 km This layer has a thickness of about 10 km and is mainly due to the burning of meteorites in the Earth’s atmosphere so that sodium is produced continuously in the mesosphere. We calculate the corresponding rate constants for temperatures between 100 K and 300 K

Interaction potential

Long-range interactions—Asymptotic potential

Method

Cross sections

Findings

CONCLUSIONS