Spin-Dependent Dissociative Excitation in a Laser Pumped Afterglow.

The energy and spin dependence of dissociating collisions between two types of noble gas metastable atoms and cadmium dihalide molecules have been studied in a flowing afterglow apparatus. The fluorescence spectra obtained in the range of 3000-7600 A which result from the Ar( ^{3}P_2) + CdX_2 interactions indicate a dominant dissociative excitation production mechanism. On the other hand, for the He(2^3S _1) + CdX_2 collisions, there appears to be competition between dissociative excitation and other "dark" channels. The emission spectra are further used to narrow the uncertainty in the currently accepted values for the dissociation energy of the CdX _2 molecules. The Wigner spin rule (conservation of total electronic spin) was verified for these processes as shown by the dominance of final state triplet production as compared to the virtual absence of singlet spin state production. In an attempt to further study the spin dependence of the dissociative excitation process, transfer of the longitudinal component of the electronic spin from oriented He(2 ^3S_1) atoms to Cd(6 ^3S_1) atoms was monitored. These data showed a null result for the transfor of the spin component, but were limited by a 3% systematic error of the apparatus. The spin dependent measurements rely on the ability to spin-polarize the He(2^3S _1) atoms by laser optical pumping methods. Four laser materials which exhibit promising characteristics for this procedure have been studied, and the results are presented for Nd^{3+}:YAP, La_{rm 1-x}Nd _{rm x}MgAl_ {11}O_{19}, Nd^{3+}:LiNbO _3, and Nd^{3+} :Silicate fibers.