Determination of the rate coefficient of the electron-impact excitation from the argon resonance states (1s₂ and 1s₄) to 2p states by the emission line ratio in an afterglow plasma

The rate coefficients of electron-impact excitation from argon 1s₂ and 1s₄ (resonance states) to 2p states are determined in the electron temperature (T_e) range of 0.5-1.1 eV. This is achieved by using a population model for Ar(2p) and measured parameters in the afterglow of an rf (60 MHz) pulsed capacitive discharge. These parameters include the densities of the 2p states (optical emission spectroscopy), the densities of the four argon 1s states (diode laser absorption), and T_e (a Langmuir probe and a line-ratio technique), for discharges with two gas mixtures: Ar(60 mTorr)/O₂(2 mTorr) and Ar(60 mTorr)/Xe(1.8 mTorr). It is found that the rate coefficients obtained in this work agree well with those from the cross sections by a large-scale R-matrix calculation reported recently by Zatsarinny et al (2004 J. Phys. B: At. Mol. Opt. Phys. 37 4693, 2014 Phys. Rev. A 89 022706).