Quenching of 4He(21S,21P) and 3He(21S,21P) states by collisions with Ne(1S0) atoms

The cross sections and rate constants for quenching He-4(2(1)S), He-4(2(1)P), He-3(2(1)S) and He-3(2(1)P) states by collisions with ground state Ne atoms are measured by a time-resolved method in a He-Ne electron beam excited plasma at low pressure. These rate constants at T-g = 600 K are: k(4He(21S)) = (1.6 +/- 0.2) x 10(-10), k(4He(21P)) = (3.4 +/- 2.5) x 10(-10), k(3He(21S)) = (1.6 +/- 0.2) x 10(-10) and k(3He(21P)) = (5.7 +/- 1.2) x 10(-11) cm(3) s(-1). The cross sections derived from the rate constant are sigma(4He(21S)) = (8.4 +/- 0.8) x 10(-16), sigma(4He(21P)) = ( 1.8 +/- 1.3) x 10(-15), sigma(3He(21S)) = (7.1 +/- 0.9) X 10(-16) and sigma(3He(21P)) = (2.6 +/- 0.5) x 10(-15) cm(2), respectively. The diffusion coefficient of He-3(2(1)S) in He-3 is estimated to be D3He(21S)-3H = 1.9D(4He(21S)-4He), based on comparison with 4He. A time-dependent collisional radiative model for an e-beam sustained He-Ne plasma is developed and the predicted line intensity of Nel lambda = 6328 Angstrom line is compared with the experimental data. The influence of different processes involved in population and depopulation dynamics of He(2(1)S) state are evaluated. (C) 2003 Elsevier Ltd. All rights reserved.