Ion–molecule reactions of N+ with CO: Integral reactive cross sections in the collision energy range 0.2–13 eV

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Abstract
The guided beam technique, which allows the precise measurement of integral reactive cross sections of ions, has been used to measure the products of the collision of N+ with CO in the energy range 0.2–20 eV (lab). All five possible ionic reaction products CO+, NO+, C+, CN+, and O+ have been observed. The cross sections of the exothermic CO+ and NO+ channels show the usual decrease with E at low E (below 3 eV lab, i.e., 1 eV c.m.), then increase again to a flat maximum (near 12 eV lab, i.e., 5 eV c.m.). The CN+ and O+ channels show the expected thresholds, then a maximum (near 8 eV lab, i.e., 6 eV c.m.), whereas the C+ channel seems to have an activation energy and is still increasing at 13 eV c.m. There is no indication, in the form of kinks, of excited product channels except for dissociation. In addition, time‐of‐flight measurements have been done, giving some information on the forward component of the product velocity. The results are discussed in the light of simple theories, and of correlation diagrams supported by partial knowledge of the potential energy surface of (NCO)+ from CI calculations by A. A. Wu. This molecule has three stable linear isomers NCO+, NOC+, and CNO+, which have also linear low lying excited states. So the discussion of the reaction as a collinear collision seems justified. The well in the 3Π states can probably explain complex formation at low energies. The products CO+ and O+ cannot be formed adiabatically (even in Cs symmetry). This is in accord with the small cross section for O+ formation, but not with the large one for CO+, where one has to postulate the existence of nonadiabatic surface ’’jumps’’. Additional experiments, especially differential cross sections, are needed for a more comprehensive discussion of the molecular dynamics, which, after all, is not singular but rather prototypical for triatomic chemical reactions.

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