Translational spectroscopy of CO 2. I. kinetic energy distribution of CO +· fragments

Abstract

The kinetic energy distribution of Co +· ions produced by dissociative electron ionization of CO 2 was determined by high resolution measurements of drift times in a time-of-flight mass spectrometer. A computational analysis of drift-time distributions, obtained at different electron energies in the range 20–50 eV, gave the corresponding kinetic energy distributions, from which the excitation functions of fixed energy ions were deduced. Breaks in the excitation functions allow us to determine the energies of ionizing electrons at which Co +· of a fixed kinetic energy begins to be produced by new different Co 2 +· states excited by Franck-Condon transitions of progressively higher energy (appearance energy of fixed kinetic energy ions, AEE). The plot showing all the breaks observable in the excitation function of ions with kinetic energy E i ( y-axis) at the corresponding electron energy E e ( x-axis), gives evidence of six well-defined groups of points, each one in good agreement with a straight line behaviour and each representing a different CO 2 +· state producing CO +· ions of increasing kinetic energy with increasing ionizing electron energy. The six x-axis intercepts give the experimental values of the dissociation limit (DL) of the six CO 2 +· states and occur at 22.2, 23.9, 26.8, 31.4, 35.2 and 38.5 eV. The slope of the six straight lines and the kinetic energy range of the CO +· ions of each state are given. A possible interpretation in terms of CO 2 +· states is reported.