$g$ and Hyperfine Components of $V_{K}$ Centers

Experimental values of the

g

and hyperfine components of

{X_{2}}^{-} - V_{K}

centers and

{Y_{2}}^{-} - V_{K}

-type centers (

X, Y = F, C l, B r, I

) in a large number of pure (

AX

) and doped (

A X : Y^{-}

) alkali halides have been determined through a careful analysis of their electron-paramagnetic-resonance (EPR) spectra. Expressions for the

g

components have been derived. For an accurate quantitative analysis, it is necessary to take into account the overlap terms in the calculation of

δ

, the matrix element of the orbital angular momentum

\vec{1}

between the

{}^{2}Σ_{u}^{+}

ground state and the

{}^{2}Π_{u}

state. A calculation for

{Cl}_{2}^{-}

yields

δ = 0.78

. Representative experimental values for

{Cl}_{2}^{-}

and

{Br}_{2}^{-}

are

δ = 0.73 and 0.70

, respectively. The

{}^{2}Σ_{u}^{+} - {}^{2}Π_{u}

energy differences thus determined decrease going from the Rb salt to the Li salt. This behavior, in general, parallels that of the

{}^{2}Σ_{u}^{+} - {}^{2}Σ_{g}^{+}

and

{}^{2}Σ_{u}^{+} - {}^{2}Π_{g}

energy differences which are known from the optical-absorption measurements. The crystal field splitting of the

{}^{2}Π_{u}

state is determined from the orthorhombic character of the

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gand Hyperfine Components ofVKCenters