HO+2 molecular ion. Geometrical structure and vibrational frequencies

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 r/sub e/(H--O) = 1.005 A, r/sub e/(O--O) = 1.239 A, theta/sub e/(HOO) = 111.50, compared to the experimental structure of neutral HO2, r0(H--O) = 0.977 A, r0(O--O) = 1.334 A, theta0(HOO) = 104.20. 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