VISIBLE AND UV EMISSION FROM RARE GAS MONOHALIDES

$^{1}$J.E. Velazco and D. W. Setser, Chem, Phys. Lett. 25 197 (1974). $^{2}$M.F. Golde and B. A. Thrush, Chem. Phys. Lett. 29, 486 (1974).""Author Institution: Avco Everett Research Laboratory, Inc., 2385 Revere Beach ParkwayEmission has been observed from excited, charge-transfer states of Xel, XeBr, XeCl, XeF, and ArF, High pressure (4-80 psia) mixtures of argon, xenon, and the halogens were irradiated with 100 ns pulses from a high intensity electron beam. The emission was recorded using time-integrated and time-resolved diagnostics. The emission was observed to rise rapidly during the electron beam pulse, evidently a result of reactions of the type $Xe^{*} + Cl_{2} - XeCl^{*} + Cl$ and $Xe_{2}^{*} + I_{2} - Xel^{*} + Xe + I$ some of which are known to be $fast.^{1,2}$ The emission decayed away in a couple hundred nanoseconds at low partial pressures, but showed evidence of quenching at halogen pressures above a few Torr. The strongest emission was observed on the $^{2}\Sigma$ $\rightarrow$ $^{2}\Sigma$ bands, which peak at 250 nm (XeI), 279 nm (XeBr) 308 nm (XeCl), 354 nm (XeF), and 260 nm (ArF). The emission from Xel drops sharply toward the red, but shades off toward the blue with only very weak structure evident. The other molecules behave similarly except that the structure becomes increasingly sharp in the lighter halogens. These features are in excellent agreement with a model based on the alkali halides to describe the excited state. The sharper structure evident in the fluorescence from the lighter halides is due to increased bonding in the ground state. Quantitative interpretations of the spectra will be presented arid compared with the molecular model. The Implications of these results for proposed rare-gas monohalide excimer lasers will be discussed