Knowledge Bank

Photoluminescence from BaF, generated in the gas phase $ Ba + SF_{6} $ reaction, is observed. The 501.7 and 496.5 nm lines of a single longitudinal mode $Ar+$ laser coincide respectively with $ BaF \ C^{2}\Pi_{1/2}\leftarrow X^{2}\Sigma $ and $ C^{2}\Pi_{3/2}\leftarrow X^{2}\Sigma $ transitions. The spectrum of C-X photoluminescence excited by the 496.5 nm line contains features associated with four distinct laser populated levels. By measuring $ R(J - 1) - P(J + 1)$ separations, the laser is shown to coincide with the $ C-X (0,0) P(41), (1,1) P(50), (2,2) P(58),$ and $(3,3)P(67)$ lines. The $ C_{3/2} - X (0,0) P(41)$ transition can be excited separately from the other three nearby lines. The spectrum of laser induced photoluminescence contains in addition to $ C_{3/2} - X $ features, strong $C1/2-X,A2\Pi 3/2-X,A2\Pi 1/2-X$ and $ B^{2}\Sigma - X $ features. The intensity ratio of $ A_{3/2} - X $ to $ A_{1/2} - X $ fluorescence is inconsistent with the usual spin selection rules or with the accepted electronic configurations of the $ C^{2}\Pi$ and $A^{2}\Pi $ states.