Unimolecular reaction paths of electronically excited species. IV. The C̃ 2Σ+g state of CO+2

Abstract

The geometrical structure of the low-lying states of CO+2 has been calculated ab initio. The C̃ 2Σ+g/2A1 state is found to be slightly bent in its equilibrium geometry. A new assignment of the vibrational structure of the corresponding band in the photoelectron spectrum is suggested. State C̃ is predissociated by two competitive channels. One of them leads to O++CO, the other to CO++O. The mechanism of these predissociations involves a slow, rate-determining, intersystem crossing to a bent ã 4B1 state. The population of state ã has a choice between dissociating to O++CO fragments and undergoing a further, much faster, intersystem crossing to the ground state X̃ which dissociates to CO++O. Since radiationless transitions between X̃ and ã are relatively rapid, the state which is lower in energy (i.e., X̃) has a much larger population than the other (i.e., ã). Hence, the CO++O channel prevails as soon as it is energetically accessible. The rate-determining step of both processes is the intersystem crossing between states C̃ and ã. Its rate constant is estimated by a statistical method due to Zahr, Preston, and Miller, recasted in a simpler form. A value of about 4×107 s−1 is obtained.

Photoelectron imaging of XUV photoionization of CO2 by 13–40 eV synchrotron radiation

“…In theoretical calculations, Praet et al 58 found that the geometry of the B-state is slightly bent with an angle of about 170 • . This bent structure probably also prevails for Rydberg series converging to the B-band.…”

Resolving Strong Field Dynamics in Cation States of CO_2 via Optimised Molecular Alignment

“…Due to the dissociation limits of the respective fragments, O + (1,0) may be produced from its vibrational ground state, whereas CO + (1,0) can only result from vibrationally excited states. The theoretical work of Praet and coworkers [15] has established the basic predissociation mechanism and has later been extended only slightly [232,236,237]. As shown in fig.…”

“…The reason being that their associated dissociation continua cannot be reached via a vertical Franck-Condon transition from the CO 2 ground state [15]. The third excited ionic state C is the first state above the lowest dissociation limit.…”

“…It has been found that the C state fully predissociates and dominates the fragmentation mechanism. Several theoretical and experimental studies have thus been performed to understand the corresponding dissociation dynamics [15,230,232,233,[235][236][237]. Due to the dissociation limits of the respective fragments, O + (1,0) may be produced from its vibrational ground state, whereas CO + (1,0) can only result from vibrationally excited states.…”

“…Firstly a rather large body of work is available on the tunneling ionisation of CO 2 [12][13][14]. Secondly, the dissociation of the molecular ion CO + 2 is relatively well understood [15]. Thirdly, the resulting fragmentation channels could be identified and isolated rather easily in the used experimental setup due to their lack of kinetic energy release [16].…”