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 a_N/2 (half the ¹⁴N-hyperfine splitting) and at 3a_N/2, strongly suggesting the existence of quartet state ¹⁴N atoms (⁴S_3/2). 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.