The HO+2 molecular ion. Geometrical structure and vibrational frequencies

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Abstract
The equilibrium geometry and harmonic vibrational frequencies of HO+2 have been predicted at seven distinct levels of ab initio theory. In this regard, self‐consistent‐field (SCF) and configuration interaction (CI) methods were used in conjunction with double zeta (DZ), double zeta plus polarization (DZ+P), and extended basis sets of contracted Gaussian functions. The molecular structure of HO+2 predicted at the DZ+P CI level of theory is re(H–O) =1.005 Å, re(O–O) =1.239 Å, θe(HOO) =111.5°, compared to the experimental structure of neutral HO2, r0(H–O)=0.977 Å, r0(O–O)=1.334 Å, θ0(HOO)=104.2°. Anharmonic vibrational frequencies were also predicted at four different levels of theory, with the DZ+P CI results being ν1=3204 cm−1, ν2=1572 cm−1, ν3=1144 cm−1. For comparison, the observed fundamentals for the neutral HO2 molecule are ν1=3436 cm−1, ν2=1392 cm−1, and ν3=1098 cm−1.