ESR spectra and structures of NaSO2 and NaO2

Abstract

We have observed the electron spin resonance (ESR) spectra of NaSO2 and NaO2, trapped in argon at 4 °K, following their production by codeposition of a beam of sodium atoms with SO2 and O2, respectively, in a large excess of argon. Each spectrum is a triplet of quartets, the triplet structure arising from an orthorhombic g tensor (g), and the quartet structure resulting from the Na hyperfine (hfs) interaction. For NaSO2, the components of g are g1=2.0024, g2=2.0060, and g3=2.0101 where axis 1 is perpendicular to the SO2 plane and axis 2 is the SO2 symmetry axis. In this axis system, the Na hfs tensor of NaSO2 is A11=−1.49, A22=−1.22, A33=−1.85, A12=0.56, and A13=A23=0.00 Oe. For NaO2, g1=2.0029, g2=2.0063, g3=2.1112, and A1=−3.5, A2=−1.8, and A3=−3.4 Oe, where axis 1 is perpendicular to the NaO2 plane and axis 3 is the O–O bond. The magnitudes of the Na hfs splittings showed that each molecule is a bound ion pair. Comparison of the observed anisotropies in the Na hfs splittings with calculated anisotropic hfs constants led to a determination of the signs of the hfs constants and gave the following structural information. NaSO2 is nonplanar with the Na+ ion located 4.3 a0 from each of the two O atoms and 4.7 a0 from the S atom. NaO2 is a π radical, and the Na+ ion is located 4.0 a0 from each of the two O atoms.