Abstract
From the study of the λλ5876, 7065 and 10830 He I line intensities in NGC 6572, NGC 6803, NGC 7009, NGC 7027, NGC 7662, and IC 418 it is found that the I(10830)/I(5876) ratio is weaker than expected. It is found that dust absorption of λ(10830) photons is not the cause for the low I(10830)/I(5876) ratios. By assuming that the 23S He0 state is depopulated only by radiative transitions to the 11S state and by triplet-singlet exchange collisions it is found that its population is about a factor of two smaller than expected. One of the main implications of the underpopulation of the 23S level is that the collisional effects in the determination of the N(He)/N(H) abundance ratios of planetary nebulae and O-poor extragalactic H II regions are smaller than previously thought. This result is important for the determination of the pregalactic helium abundance.
