The Influence of the Method of Excitation on Transition Probabilities in Sodium Vapor

Abstract

Fluorescence has been excited in sodium vapor at 180°C by illuminating with the second member of the principal series, $\lambda =3303\mathrm{}\mathrm{A}$. Both the first and second members of the principal series appeared in the fluorescence, the first member being due to the atom returning to its normal state in steps. The ratio of the intensities of the two lines was determined by photographic photometry and the results compared with what might be expected on the basis of measurements by Weiss on the sodium arc. In the arc the atom returns to the normal state from the $3P$ by way of the $2S$ twentyfive times as often as the direct transition occurs whereas in fluorescence approximately the same number take each path. This is contrary to the usual assumption that the transition probabilities are independent of the method of excitation.