Ground-state energy, impact

There are significant differences between tliese two types of reactions as far as how they are treated experimentally and theoretically. Photodissociation typically involves excitation to an excited electronic state, whereas bimolecular reactions often occur on the ground-state potential energy surface for a reaction. In addition, the initial conditions are very different. In bimolecular collisions one has no control over the reactant orbital angular momentum (impact parameter), whereas m photodissociation one can start with cold molecules with total angular momentum 0. Nonetheless, many theoretical constructs and experimental methods can be applied to both types of reactions, and from the point of view of this chapter their similarities are more important than their differences. 

Excitation and ionization have a common origin-namely, raising the electronic level of an atom or a molecule from its ground state to a state of higher energy via the impact of charged particles or photons. Nevertheless, their chemical fates can be drastically different. In this chapter, we treat these phenomena descriptively. 

C0+ are nonreactive. These processes have rather high endoergicities (5.5 to 5.6 eV), based on calculations for the ground-state reactants. The energies required to form the excited reactant ions in these instances ( 20 to 23 eV) are not readily accessible with ordinary photoionization sources 85 therefore, these reactions have been studied only with electron-impact ionization. The identity of the excited state responsible for the analogous reaction... 

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