EPR study of NaCl: CO2– and NaCl : SO2–

Abstract

Two new triatomic molecular ions with C_2v symmetry i.e. CO₂^– and SO₂^– have been detected in NaCl by means of EPR. By analysing the ¹³C hyperfine tensor of the CO₂^– radical the spin densities in the 2s and 2p_z carbon atomic orbitals can be calculated. Since the ¹⁴N hyperfine tensor of the isoelectronic NO₂ molecule in the same host lattice is also known, a comparison between the spin densities in both defects can be made. In addition, the spin densities for both defects are calculated using ab initio methods and are compared with the experimental results.

As is the case for the smaller CO₂^– ion, the SO₂^– radical is assumed to substitute for only one halide ion. The monovacancy model for the SO₂^– ion is discussed. Such a model is in accordance with that for the smaller ozonide O₃^– ion. On the other hand, the larger S₃ and Se₃^– ions occupy a trivacancy site.