The electronic structure of HO2+

Global Potential Energy Surface for HO2+ Using the CHIPR Method

An analytical potential energy function for the title ion based on the combined hyperbolic inverse power representation (CHIPR) method and its characteristics are discussed at length in the present work. The curves of two diatomic ions, O₂⁺ and OH⁺, are also obtained within the same approach. The model PES so obtained exhibits extraordinary flexibility in describing with subchemical accuracy even the weak topological features near the higher energy regions. Thus, structural properties predicted by the model may help spectroscopists who want to compare their experimental values with the ones from theory. The relaxed PESs in various coordinates have been calculated by relaxing the O₂ bond distance using the present model, thus throwing light on all the possible isomers and their interconversions. The latest estimates of IR frequencies for three vibrational modes have been compared with the computed frequencies using the present model, and the agreement seems encouraging.

High-resolution infrared spectroscopy of O2H+ in a cryogenic ion trap

The protonated oxygen molecule, O₂H⁺, and its helium complex, He-O₂H⁺, have been investigated by vibrational action spectroscopy in a cryogenic 22-pole ion trap. For the He-O₂H⁺ complex, the frequencies of three vibrational bands have been determined by predissociation spectroscopy. The elusive O₂H⁺ has been characterized for the first time by high-resolution rovibrational spectroscopy via its ν₁ OH-stretching band. Thirty-eight rovibrational fine structure transitions with partly resolved hyperfine satellites were measured (56 resolved lines in total). Spectroscopic parameters were determined by fitting the observed lines with an effective Hamiltonian for an asymmetric rotor in a triplet electronic ground state, X̃³A^'', yielding a band origin at 3016.73 cm^-1. Based on these spectroscopic parameters, the rotational spectrum is predicted, but not yet detected.

Ab initio adiabatic and quasidiabatic potential energy surfaces of lowest four electronic states of the H+ + O2 system

Ab initio global adiabatic and quasidiabatic potential energy surfaces of lowest four electronic (1-4  (3)A(")) states of the H(+)+O(2) system have been computed in the Jacobi coordinates (R,r,γ) using Dunning's cc-pVTZ basis set at the internally contracted multireference (single and double) configuration interaction level of accuracy, which are relevant to the dynamics studies of inelastic vibrational and charge transfer processes observed in the scattering experiments. The computed equilibrium geometry parameters of the bound [HO(2)](+) ion in the ground electronic state and other parameters for the transition state for the isomerization process, HOO(+)⇌OOH(+) are in good quantitative agreement with those available from the high level ab initio calculations, thus lending credence to the accuracy of the potential energy surfaces. The nonadiabatic couplings between the electronic states have been analyzed in both the adiabatic and quasidiabatic frameworks by computing the nonadiabatic coupling matrix elements and the coupling potentials, respectively. It is inferred that the dynamics of energy transfer processes in the scattering experiments carried out in the range of 9.5-23 eV would involve all the four electronic states.

Nonadiabatic dynamics on the two coupled electronic PESs: the H+ + O2 system

Multistate adiabatic and diabatic PESs were computed for the H+ + O2 collision system in Jacobi coordinates, (R,r,γ) using the cc-pVTZ basis set and the ic-MRCI level of theory. In addition, all possible interaction potentials and nonadiabatic coupling matrix elements among those different electronic states were also computed. Comparisons with earlier computed interaction potentials were made wherever possible, and the differences between them is attributed to the multistate diabatization and the chosen level of theory and basis set. Focusing our attention on the ground-state (GS) and the first excited-state (ES) PES, quantum dynamics were performed using the 2 × 2 diabatic potential submatrix obtained from the multistate (four) diabatic potential matrix within the VCC-RIOSA scheme at two experimentally reported collision energies, E(cm) = 9.5 and 23 eV. The scattering quantities were computed for two experimentally observed collision processes, namely, the inelastic vibrational excitation (IVE), H+ + O2 (X3Σg(−),v = 0) → H+ + O2 (X3Σg(−),v′), and the vibrational charge transfer (VCT), H+ + O2 (X3Σg(−),v = 0) → H (2S) + O (X2Πg,v′′). Comparisons were made with experimental results and found an overall improvement relative to the earlier computed results, and the discrepancies, if any, could be brought down to minimum by further modification in employed ab initio PESs and the interaction potential.

Ab initio potential energy surfaces and nonadiabatic collision dynamics in H(+)+O(2) system

The adiabatic potential energy surfaces for the lowest five electronic states of (3)A" symmetry for the H(+)+O(2) collision system have been obtained at the multireference configuration interaction level of accuracy using Dunning's correlation consistent polarized valence triple zeta basis set. The radial nonadiabatic coupling terms and the mixing angle between the lowest two electronic states (1 (3)A" and 2 (3)A"), which adiabatically correlate in the asymptotic limit to H((2)S)+O(2) (+)(X (2)Pi(g)) and H(+)+O(2)(X (3)Sigma(g)(-)), respectively, have been computed using ab initio procedures at the same level of accuracy to yield the corresponding quasidiabatic potential energy matrix. The computed strengths of the vibrational coupling matrix elements reflect the trend observed for inelastic vibrational excitations of O(2) in the experiments at collision energy of 9.5 eV. The quantum dynamics has been preformed on the newly obtained coupled quasidiabatic potential energy surfaces under the vibrational close-coupling rotational infinite-order sudden framework at the experimental collision energy of 9.5 eV. The present theoretical results for vibrational elastic/inelastic excitations of O(2) are in overall good agreement with the available experimental data obtained from the proton energy-loss spectra in molecular beam experiments [F. A. Gianturco et al., J. Phys. B 14, 667 (1981)]. The results for the complementary charge transfer processes are also presented at this collision energy.