Electronic ground state assignment for O+4: Neon matrix electron-spin resonance investigation

Abstract

The O⁺₄ radical cation has been generated by two different methods and trapped as an isolated ion in neon matrices at 4 K for electron‐spin resonance (ESR) investigation. The O⁺₄ species is a potentially important atmospheric ion for which little experimental or theoretical information is available. These ESR results indicate that the electronic ground state of O⁺₄ is a nonlinear quartet (S=3/2) with the three unpaired electrons occupying primarily 2p(π) orbitals. The fine structure‐parameters obtained from an analysis of the ESR spectrum are D=1.875(5) and E=0.0350(5) cm⁻¹ . The isotopic ions^16,17 O⁺₄ were also generated but the ¹⁷ O hfs could not be fully analyzed because of the large number of overlapping hyperfine lines.