Theoretical He I line intensities in gaseous nebulae: NGC 1976, 6572 and IC 4997

Smits has recently calculated theoretical He I intensities for a large number of lines for conditions appropriate to gaseous nebulae. These are likely to remain the definitive calculations for some time to come. A comparison of these line ratios with observed values in three nebulae reveals some discrepancies. We show that these discrepancies are reduced when collisional effects from the metastable 2³S level are included, and that it is not necessary to invoke an unknown depopulation mechanism for the He I 2³S level.