An EPR and ENDOR study of quartet state nitrogen atoms trapped in irradiated NaN3 powder

Abstract

The nature of quartet state nitrogen atoms formed in γ-irradiated NaN3 powder was investigated by EPR, ENDOR and ENDOR-induced EPR (EIE). The ENDOR spectrum observed at 110 K clearly showed two sets of 14N signal pairs centered at aN/2 (half the 14N-hyperfine splitting) and at 3aN/2, strongly suggesting the existence of quartet state 14N atoms (4S3/2). At 160 K, the EPR spectrum exhibited a clear fine structure accompanied by a hyperfine coupling due to 14N. The zero-field splitting, D, gradually increased with decreasing temperature from 170 to 40 K, and then became nearly constant. The temperature dependence of D was explained in terms of a local lattice vibration coupled with spin states of 14N atoms. At below 95 K, a new fine structure with larger D was observed. The observed two D-values were attributed to 14N atoms located at two different interstitial sites in the monoclinic NaN3 structure.