Search

The rare‐gas monohalides are simple diatomic molecules whose properties and emission spectra were essentially unknown as recently as four years ago. Now they are the active media for gas lasers that could provide overall electrical efficiency as high as 10%. These lasers operate in the ultraviolet and vacuum‐ultraviolet spectral regions and are the first lasers outside the infrared region that appear to be scalable to high single‐pulse energy (greater that 100 joules per pulse) with high average power and efficiency. Not surprisingly in light of the species' novelty and the laser's promised utility (for example, in photochemical‐separation schemes), research and development in this area has grown remarkably since the first laser demonstration three years ago.

The primary dissociation step for alkali halide diatomics in argon has been studied in order to determine whether collisional dissociation produces ions, atoms, or a mixture of both types of products. The method is based on time‐resolved absorption spectroscopy of shock‐heated vapors. Results show that the cesium halides, and the rubidium and potassium halides, with the exception of the two iodides, dissociate essentially completely to ions; that the lithium salts and NaI and NaBr dissociate essentially completely to atoms; and that the other alkali halides (KI, RbI, NaCl, and probably NaF) dissociate to mixtures of atoms and ions, at least under some conditions. The branching ratio of atom pairs/ion pairs is interpreted in terms of the effective width of the adiabatic dissociation channel, compared with the spacing of the vibrational levels of the diabatic bound state.

The dissociation of diatomic CsBr molecules in a shock wave has been studied by time‐resolved absorption spectroscopy. Absorption by neutral cesium atoms increases monotonically toward its equilibrium value as dissociation proceeds, but under a wide range of conditions, absorption by Br− ions goes rapidly to a maximum and then falls to its equilibrium value. The results show that under some conditions, the principal primary products of dissociation are ions, rather than atoms or a thermally equilibrated mixture of atoms and ions.