On the branching ratios of several pairs of He(II) lines

Branching ratios of He(II) lines have been measured for the principal levels 5–10. The observations have been made on an He plasma produced by a hollow cathode-arc discharge, having an electron density of 3×10¹⁹m^-3 and an electron temperature of 2×10⁵ K on the axis of the discharge.The observed branching ratios differ by about 30% from the ones following from theoretical transition probabilities, if the sublevels of the main levels were populated according to their statistical weights. The shape of the He(II) 4686Åemission line observed off the axis of the discharge using a Fabry-Pérot interferometer gave evidence of a non-statistical population distribution for the sublevels.