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

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 ions16,17 O+4 were also generated but the 17 O hfs could not be fully analyzed because of the large number of overlapping hyperfine lines.