Atomic data for opacity calculations: XII. Line-profile parameters for neutral atoms of He, C, N and O

For a transition between two levels p and p' let Gamma (p,p') be the linewidth for plasma broadening, in energy units and per unit density. An empirical formula is used, Gamma (p,p')=a(R p +R p' ) B T C where R p ' R p' are mean-square radii and T the temperature. For 91 transitions in C, N and O, values of the coefficients a, B and C are obtained on making least-squares fits of log( Gamma ) to results of calculations by Griem (1974). Values of Gamma obtained from the formula are compared with those from experimental measurements for 58 transitions in C, N and O. The agreement is generally satisfactory and it is concluded that the formula will give results of an accuracy adequate for opacity calculations. For He I, accurate calculations of Gamma have been made by Griem (1974) for 40 transitions and these values are used directly for the opacity work. The empirical formula is used only for those transitions in He I for which accurate calculations have not been made.