Paramagnetic Resonance ofF2−Ions Trapped in Electron-Irradiated Potassium Bifluoride

Abstract

Electron-spin resonance (ESR) spectra attributed to ${\mathrm{F}}_{2}^{\ensuremath{-}}$ molecular ions located at two inequivalent anion sites were observed at 9.2 Gc/sec after electron bombardment of single crystals of potassium bifluoride (KH${\mathrm{F}}_{2}$) at 77\ifmmode^\circ\else\textdegree\fi{}K. The molecular axis of the ${\mathrm{F}}_{2}^{\ensuremath{-}}$ ion lies along [110] or along [$1\overline{1}0$], and the spectrum for each site consists of four hyperfine resonances. They derive from a hole interacting equally with two nuclei of spin \textonehalf{}, giving an effective nuclear spin of 0 or 1 and a highly anisotropic A tensor. For $z\ensuremath{\parallel}[110]$, $x\ensuremath{\parallel}[001]$, and $y\ensuremath{\parallel}[1\overline{1}0]$, components of the g and A tensors for 77\ifmmode^\circ\else\textdegree\fi{}K are ${g}_{z}=2.0020\ifmmode\pm\else\textpm\fi{}0.001$, ${g}_{x}\ensuremath{\approx}{g}_{y}=2.0168\ifmmode\pm\else\textpm\fi{}0.001$, ${A}_{z}=955.4\ifmmode\pm\else\textpm\fi{}1$ G, and ${A}_{x}\ensuremath{\approx}{A}_{y}=21\ifmmode\pm\else\textpm\fi{}4$ G. At room temperature ${g}_{z}=2.0024\ifmmode\pm\else\textpm\fi{}0.001$, ${g}_{x}\ensuremath{\approx}{g}_{y}=2.0180\ifmmode\pm\else\textpm\fi{}0.0015$, ${A}_{z}=928.8\ifmmode\pm\else\textpm\fi{}1$ G, ${A}_{x}=35.5\ifmmode\pm\else\textpm\fi{}1$ G, and ${A}_{y}=25.5\ifmmode\pm\else\textpm\fi{}3$ G. The crystal changed from colorless to intense green upon electron irradiation, with optical absorption bands at 2.0 and 4.1 eV. As the sample was brought to room temperature, the 2.0-eV band rapidly annealed, whereas the 4.1-eV band showed annealing behavior similar to the spin resonances, remaining about two days. The ESR spectra resulted from electron irradiations with electron energies as low as 0.15 MeV, but not from a ${10}^{6}$-R dose of ${\mathrm{Co}}^{60}$ gamma rays.