Stability, Spectroscopic Constants, and Dissociation of CO 2+ : A Theoretical Study BHASKAR MONDAL, NARAYAN C. BERA, ABHIJIT K. DAS Department of Spectroscopy, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700 032, India Received 7 May 2008; accepted 11 June 2008 Published online 18 September 2008 in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/qua.21847 ABSTRACT: Stability, spectroscopic constants, and dissociation of CO 2+ have been studied in detail using ab initio MP2, CCSD and CCSD(T) methods, and density functional B3LYP method. The stability and the ambiguity between the ground and metastable state of the molecular dication have been discussed. The spectroscopic constants of the molecular dication have been compared with the experimental and theoretical values wherever available. Various charge symmetric and charge asymmetric dissociation pathways of CO 2+ have been investigated. After dissociation, the fragmented atoms and ions are considered to be either in their ground or in their metastable state. Interesting results have been obtained for the charge symmetric and charge asymmetric dissociation of the diatomic dication. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem 109: 469 – 476, 2009 Key words: stability; spectroscopic constants; dissociation; CO 2+ dication; ab initio; B3LYP study Introduction M olecular dications are most easily formed by the double ionization of neutral molecules. The chemical bonds become considerably weaker if the two electrons are ionized from the valence shell of a molecule. The Coulomb repulsion between the two nuclei can no longer be compensated by chem- ical bonding and consequently the molecule disso- ciates into atoms and ions. However, in some mol- ecules when both electrons are removed from the nonbonding orbitals, or when the molecules have multiple-bond structure, the molecular dications are still stable or quasi-stable with respect to disso- ciation. In such diatomic molecular dications, the chemical bonding is sufficient to overcome the Cou- lomb repulsion and create potential well. These stable or quasi-stable dications play an important role in plasma occurred in the ionosphere and in interstellar medium. Molecular dications are also highly chemically reactive due to long-range inter- Correspondence to: A. K. Das; e-mail: spakd@iacs.res.in International Journal of Quantum Chemistry, Vol 109, 469 – 476 (2009) © 2008 Wiley Periodicals, Inc.