A relation between the breadths of the 3d9f lines of lanthanum and their relative intensities in absorption and emission

It is argued that differences between the relative intensities of M IV and M V spectra of lanthanum in absorption and emission can be accounted for by autoionisation within a simple 'quasi-atomic' model. A relation is given between the breadths of the 3d 9 f lines and the change of relative intensities from absorption to emission.