Ultramarine study by EPR

By EPR, ion‐radicals ˙ S − , ˙ S   2 − , and ˙ S   3 −are found to arise in the process of synthesizing ultramarine. Typical, blue ultramarine contains ˙ S   3 −ions. At room temperature, the line width is found to be determined to a large extent by spin–lattice interaction, whereas at liquid nitrogen temperature (77° K) almost exclusively by spin–spin interaction. The EPR line shape was analyzed by linear anamorphosis of the resonance curve. The second moment was used for computing the density of polysulfide ions ˙ S   3 −according to Van Vleck's formula. The results indicate that the ˙ S   3 −radicals form a face centred cubic lattice in an elementary cell with lattice constant d ′ = 2 d = 18.12 Å, where d is the lattice constant of the elementary cell determined by the X‐ray method.