Reaction kinetics of the He(2P) and the He₂*(a,v) states in high-density helium

Helium at pressures ranging from 0.5 to 8 bar is excited by an intense e-beam. The absolute population densities of the He(2 1P), He(2 3P) and He2*(a,v), v=0, 1, 2 states are determined by measuring the transient absorption of probe light delivered by a dye laser. The experimental data are readily described by a kinetic model taking into account the excitation and the de-excitation processes. The recombination of He2+ by a termolecular reaction with e+He to He(2 3P) as proposed by Bates (1984) is confirmed quantitatively. The rate constants for the termolecular reactions of He(2 1P) and He(2 3P) were deduced to be (1.8+or-0.4)*10-31 cm6 s-1 and (1.6+or-0.4)*10-32 cm6 s-1 respectively. The rotational and vibrational relaxation of He2(a) by helium is investigated.