Abstract
Correlated optical and EPR studies show that after $x$- or $\ensuremath{\gamma}$-ray irradiation combined with proper thermal treatment, Br${\mathrm{Cl}}^{\ensuremath{-}}$ molecule ions aligned along the six 110> directions are present in crystals of KCl doped with a small amount of KBr. The Br${\mathrm{Cl}}^{\ensuremath{-}}$ molecule ions, which have a strong $\ensuremath{\sigma}$-polarized transition at 382 nm and a much weaker but still somewhat $\ensuremath{\sigma}$-polarized transition at 760 nm, are thermally more stable than the ${V}_{K}$ centers (${\mathrm{Cl}}_{2}^{\ensuremath{-}}$) from which they are formed. The increased thermal stability of Br${\mathrm{Cl}}^{\ensuremath{-}}$ is believed to arise primarily because the electronegativity of chlorine is greater than that of bromine. A study of the reorientation kinetics at 88\ifmmode^\circ\else\textdegree\fi{}K reveals that the reorientation of Br${\mathrm{Cl}}^{\ensuremath{-}}$ proceeds by 90\ifmmode^\circ\else\textdegree\fi{} jumps as well as 60\ifmmode^\circ\else\textdegree\fi{} jumps, and very probably also by 120\ifmmode^\circ\else\textdegree\fi{} jumps, whereas many homonuclear molecule ions reorient only by 60\ifmmode^\circ\else\textdegree\fi{} jumps.
Published Version
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