ESR Studies of N32− and N2− Molecular Ions in Anhydrous Barium Azide

Crystals of anhydrous barium azide, Ba(N3)2, have been exposed to 2537-Å ultraviolet light at room temperature. This process leads to the production of the N2− molecular ion which has been previously identified by electron spin resonance. Further ESR studies reveal that a second irradiation at low temperatures with light in a broad band of wavelengths centered at 325 nm partially bleaches the N2− and produces a new center which is identified by ESR as an N32− ion in a Type II azide ion site. Light in a second broad band of wavelengths centered at 425 nm accomplishes the reverse reaction. The angular variation of the ESR spectrum of the new center is expressed by the spin Hamiltonian: H = βH·g·S + I1·A1·S + I2·A2·S + I3·A3·S, with S = 12, I1 = I2 = I3 = 1, and A1 = A2. The principal values of g, A1, and A3 are: gx = 2.004 ± 0.001, gy = 1.996 ± 0.001, gz = 2.000 ± 0.001, Ax1 = 7.5 ± 0.5 G, Ay1 = 14.0 ± 0.5 G, Az1 = 6.2 ± 0.5 G, Ax3 = 19.6 ± 0.5 G, Ay3 = 28.0 ± 0.5 G, Az3 = 15.7 ± 0.5 G.