Transition Probabilities and Quenching in the3PState of Sodium

Abstract

The effect of foreign gases upon the fluorescence of sodium vapor excited by the second line of the principal series has been investigated. The gases used were helium, nitrogen, and hydrogen and the intensities of both the 3303A line and the $D$ light were observed. From the variation in intensity of the 3303A line as gas is added it is concluded that the presence of an inert gas has no appreciable effect upon the relative transition probabilities in the $3^{2}P$ state of sodium. With nitrogen or hydrogen as the added gas the $D$ light intensity variation followed that of the 3303A line very closely but with helium a marked increase in intensity was produced by the first gas added with a decrease at higher pressures. This increase was explained as due to a transfer of sodium atoms from the $3^{2}P$ to the $3^{2}D$ state by collisions, thus increasing the number of atoms which radiate the $D$ light. In addition to this increase in number the collisional transfers produced an increased "Doppler width" in the $D$ light which persisted up to pressures well over 100 mm of helium and caused a decreased absorption of the fluorescence light. The bearing of this work on the difference in the intensity ratio of the $2^{2}S-3^{2}P$ and $1^{2}S-3^{2}P$ transitions as reported by Weiss for an arc and by Christensen and Rollefson in fluorescence is discussed. It is concluded on the basis of experimental evidence that any explanation of the difference which depends upon multiplicity of the $3^{2}P$ state is incorrect. An explanation of this difference based upon the assumption that the life period of an excited atom varies inversely as the transition probability of the radiation emitted is presented. It is shown that recent work on the life periods of atoms in the $2^3{S}_1$ state of mercury at least partially supports this assumption. A new type of sodium arc with increased intensity and stability of operation is described.