Kinetic-energy release in the dissociation of CO22+

Abstract

The kinetic-energy release distributions (KERDs) of the fragment ion pairs (O++CO+ and C++O+) produced in dissociative double photoionization of carbon dioxide have been determined by analyzing the photoion–photoion coincidence spectra measured in the region hν=40–100 eV by use of a time-of-flight mass spectrometer and synchrotron radiation. The mechanism of the three-body dissociation (CO2+2→C++O++O) has been examined to take place sequentially via CO+ by a triple photoelectron–photoion–photoion coincidence experiment. The KERD observed for the O++CO+ and C++O+ channels at low excitation energies cannot be explained by a simple framework whereby a doubly charged molecular ion (AB2+) is directly produced on single photon absorption followed by the dissociation of AB2+ into two ionic fragments. Some of the ion pairs are produced through indirect processes in which highly excited CO2*+ and CO2** (double Rydberg) states converging to the high-lying CO2+2 electronic states autoionize before and after dissociation. From the observed KERDs for the O++CO+ and C++O+ channels of CO2+2, the range of the intercharge distances of two positive holes is estimated by assuming that the KER is given purely by Coulomb repulsion.