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 Title: Electronic structure and spectroscopy of O2 and O2+ Author(s): Vazquez, Gabriel J.; Lefebvre-Brion, H.; Liebermann, Hans P. Subject(s): Comparing theory and experiment Abstract: We carried out a comprehensive SCF MRD--CI ab initio study of the electronic structure of O$_2$ and O$_2^+$. Potential energy curves (PECs) of about 150 electronic states of O$_2$ and about 100 of O$_2^+$, as well as a number of states of O$_2^{++}$ were computed. The cc--pVQZ basis set augmented with diffuse functions was employed. Spectroscopic parameters ($T_e, T_v, \omega_e, \omega_ex_e, B_e,$ $D_e, D_0$, $\mu$, IP, etc.) are reported. A preliminary sample of the results will be presented. The electronic absorption spectrum of O$_2$ has proved difficult to analyze/interpret due to the unusually large number of electronic states which arise from the peculiar open--shell structure of both the oxygen atomic fragments and the O$_2$ molecule. For instance, there are 62 valence molecular electronic states which correlate to the six lowest dissociation limits resulting from the three valence O atom fragment states ($^3$P, $^1$D, $^1$S). In addition, there are several $nl\lambda$ Rydberg series converging to the X$^2\Pi_g$ ground ionic state and to the lowest two excited states of the cation, a$^4\Pi_u$$_i and A^2\Pi_u. Furthermore, a number of interactions of various types among several electronic states result in rovibronic perturbations which manifest themselves, e.g., as irregular vibronic structure, hence severely complicating the assignment of the absorption features and the analysis and interpretation of the spectrum. An overview of the electronic states and spectroscopy of O_2 will be presented. A chief motivation of this study of O_2 was to try to provide a theoretical insight on the nature, energetic position, shape, and dissociation asymptotes, of electronic states located in the 4 eV energy region encompassed between the O_2^+ ground state X^2\Pi_g (IP=12.07 eV) and the first excited state of the cation a^4\Pi_u$$_i$ (IP$=16.10$ eV). This in order to aid in the interpretation of experimental data related to the mechanism(s) of the neutral dissociation of the O$_2^{**}$ (Rydberg) superexcited states, which competes with autoionization. We are currently striving to compute PECs of relatively highly excited states of O$_2$ located in the 12--16 eV energy region which might help to visualize possible pathways for the neutral XUV photodissociation of the I, I$^{\prime}$ and I$^{\prime\prime}$ $^3\Pi_u$ superexcited states of O$_2$ leading to the O($^3$P) + O$^{*}$($^3$S, $^5$S) dissociation limits. Issue Date: 2014-06-18 Publisher: International Symposium on Molecular Spectroscopy Citation Info: Vazquez, G.J.; Liebermann, H.P.; Lefebvre-Brion, H. ELECTRONIC STRUCTURE AND SPECTROSCOPY OF O2 AND O2+. Proceedings of the International Symposium on Molecular Spectroscopy, Urbana, IL, June 16-21, 2014. DOI: 10.15278/isms.2014.WI12 Genre: Conference Paper / Presentation Type: Text Language: English URI: http://hdl.handle.net/2142/59156 DOI: https://doi.org/10.15278/isms.2014.WI12 Rights Information: Copyright 2014 by the authors. Licensed under a Creative Commons Attribution 4.0 International License. http://creativecommons.org/licenses/by/4.0/ Date Available in IDEALS: 2014-12-082015-04-14
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