Single crystals of synthetic BeO which have been irradiated with 6hyphen;MeV electrons show an ESR spectrum at room temperature identified as being due to boron ions substituting for beryllium at normal lattice sites. The hyperfine tensor A is cylindrically symmetric with its principal axis pointing towards one of the near oxygen bonds. Six equivalent directions are observed corresponding to the positions of the nonaxial nearesthyphen;neighbor oxygen atoms. The constants of the spin Hamiltonian are:gpar; = 2.0035plusmn;0.0005,gperp;= 2.0044plusmn;0.0005,Apar; = 122 Oe,Aperp;= 76.5 Oe. The spectrum is analyzed in terms of the paramagnetic electron occupying an antibonding orbital located along the direction of a Bsngbnd;O bond. Comparison of the observed hyperfine interaction with those expected for the free atom suggests deviations of the orbital from tetrahedralsp3configuration to one in which the ratio of theptoscontribution increases from radic;3 to 2.64, implying that the Bsngbnd;O bond is lengthened along the direction in which the paramagnetic electron is stabilized, the bond angle decreasing from 109 to 105 deg.
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