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.