Abstract
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 .

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