Spatial-anisotropy and polarized-atomic-fluorescence measurements following molecular photodissociation

A study has been made of the photodissociation of the molecules NaI, TlI, Hg${\mathrm{Br}}_2$, and Pb${\mathrm{Br}}_2$ by polarized 193-nm ArF laser light. A significant degree of polarized fluorescence was measured from excited photoproducts Tl and HgBr. No polarization was observed in the Na and Pb fluorescence, while the Hg polarization was small. For Tl the spatial anisotropy of the dissociated atoms was also measured by atomic absorption, yielding an asymmetry parameter value of $\beta =1.2\mathrm{}$. The best current explanation for the polarized Hg and Tl emission is that fine-structure and hyperfine-structure magnetic substates, respectively, are preferentially populated by the dissociation process.