Abstract
The non-resonance contributions to the self-broadening of the helium singlet lines 21S-n1P, n=3, 4, 5; 21P-n1S, n=3, 4, 5, 6 and 21P-n1D, n=3, 4, 5 are calculated within a semiclassical impact model of pressure broadening. The S-matrix elements for the 1S, 1P and 1D levels are determined from the first-order coupled equations of time-dependent perturbation theory in which the collision between the excited helium emitter and ground state helium perturber is described in terms of adiabatic molecular potentials based upon model potential expressions for the interacting atoms. If the resonance and non-resonance contributions are assumed to be additive, the agreement between theory and experiment is generally better than 30%. However for transitions involving the highly excited states 51S, 61S and 51D the theoretical results are higher than experiment by up to 50%.
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