Probing the quantal identity of low-lying electronic states ofCO2+by quantum-chemical calculations and ion-translational-energy spectrometry

Abstract

Potential-energy curves of various electronic states of CO + and CO+ are computed using allelectron ab initio molecular-orbital methods. Configuration-interaction eR'ects are treated by perturbative techniques (using Moiler-Plesset perturbation theory to fourth order) and by variational methods (using the coupled-cluster approach). In the case of CO +, calculations indicate that the lowest-energy II and E+ states are nearly degenerate in the Franck-Condon region but that only the latter is likely to be metastable; the former is expected to predissociate rapidly due to a curve crossing with a purely repulsive E state. Experimental measurements have been carried out on the kinetic energy released when metastable CO + ions dissociate by a tunneling mechanism, using an ion-translational-energy spectrometer. The kinetic-energy spectra are measured of fragment ions produced when CO + dissociates via an intermediate highly excited (dissociative) CO+' state populated in an electron-capture reaction in collision with He. The experimental results remain di%cult to interpret within the framework of the computed potential-energy curves.PACS number(s): 31.20.Ej, 34.50.Gb, 35.20.Gs

Potential energy curves for neutral and multiply charged carbon monoxide

“…Hence it is expected to play an important role in the dissociation process. These observations are in accord with the earlier reported results [12,13]. The equilibrium bond lengths for 1 Σ + and 3 Π state are found to be 1.…”

“…Experimental and theoretical results available on multiply charged ions have been reviewed elsewhere [9,10]. Although both mono and dications of CO have been investigated extensively [11][12][13][14][15][16][17][18], very few theoretical results are available on trication [19,20]. To the best of our knowledge, there is only one unrestricted Hartree-Fock and MP2 calculation reported for higher charged CO [8].…”

Very slow spontaneous dissociation ofCO2+observed by means of a heavy ion storage ring

“…This is a sufficiently long time for establishing the occurrence of the unimolecular process CO 24 " -• C^ + O" 1 " [6][7][8][9]. However, the precursor state for this process and the mechanism leading to the fragmentation have been much debated [1,[5][6][7][8][9][10][11][12][13][14][15][16][17], and it is as yet unclear whether CO 2 " 1 " contains levels that are stable on mass spectrometer instrumental time scale [6][7][8].…”

Ionic fragmentation of the CO molecule by impact of 10-keV electrons: Kinetic-energy-release distributions

“…Table IV indicates that the 1 + and 1 states significantly contribute to the KERD, while the contribution of the 3 state is probably smaller. The metastable states 1 + and 1 most probably dissociate into C + ( 2 P ) + O + ( 2 D) by tunneling through the potential barrier because their coupling with the 3 − repulsive state yields a KER value above 5.0 eV [20,29]. However, the 3 state predissociates via the 3 − repulsive state into C + ( 2 P ) + O + ( 4 S) [20].…”

“…The electron-impact-induced fragmentation of the molecule can provide information about different electronic states of the multiply charged molecular ion. A large number of theoretical studies have been made on the potential-energy surfaces of CO + and CO 2+ ions [19,20,27,[29][30][31], while only a few studies are available for triply and higher charged molecular ions [6,32]. The advent of position sensitive detectors coupled with a time of flight (TOF) spectrometer enables us to detect correlated fragment ions with their respective positions and time of flight information which, in turn, provide valuable information on the fragmentation dynamics of the precursor molecule.…”