Elastic cross sections, excitation exchange cross sections, and rate constants for excitation and quenching in N(4𝑆)-N(2𝐷) collisions.

Differential, integrated, and transport cross sections were calculated for collisions involving ground state nitrogen atoms N(4S) and first excited state N(2D) nitrogen atoms, based on high quality electronic structure potential curves and couplings. The same data set for the excitation exchange cross section was also calculated.

The rate constant for excitation in collisions of ground state atoms and the rate constant for quenching (reverse process) in collisions between ground and excited atoms were calculated using a quantum scattering method and compared with the results of the Landau–Zener and Zhu–Nakamura semiclassical methods. Note that in particular above 10,000 K rate constants for excitation and quenching are of the same order, so both should be useful in high temperature modeling.

Comparison of the resulting collision integrals with ones from other studies shows the sensitivity of treatment of the long range interactions at low temperatures. The reported excitation exchange cross sections result in excitation exchange collision integrals significantly differing from another study, which means that for this quantity the classical approach generates significant errors.

In case of collisional excitation, the simple Landau–Zener method is applicable, especially at higher temperatures. In case of quenching, neither Landau–Zener or Zhu–Nakamura approaches were able to properly describe high temperature behavior of rate constant.