HE(4P-3) SUBLEVEL QUENCHING BY ELECTRON COLLISION

The quenching by electron collisions of the He(4(3)P) sublevel has been studied by a laser resonance fluorescence method. The sublevel is optically pumped by a dye laser tuned to the transition 2(3)S-4(3)P, and the fluorescence from 4(3)P itself and from the 4(3)D state is observed and analysed. The measurement is performed at various times in the post discharge of a pulsed RF discharge, and it is correlated to the decay of the electron random flux. The latter is measured simultaneously by a time resolved Langmuir probe technique. Combination of the two results allows the measurement of the electron collision rate constants k(el)(4(3)P) = (1.23 +/- 0.34) x 10(-4) cm(3) s(-1), for the total quenching of 4(3)P, and k(el)(4(3)P --> 4(4)D) = (1 +/- 0.24) x 10(-4) cm(3) s(-1). Such rate constants turn out to be constant, within the experimental accuracy, in the range 0.2-0.6 eV of electron average energy. A good agreement is obtained with theoretical calculations. The importance of electron collisions is also demonstrated by a qualitative analysis of the fluorescence from 5(3)D, 4(1)D states.