An experimental study of the bridged and classical structures of the ethyl radical and cation by neutralized ion-beam spectroscopy

The states of ethyl radicals formed in electron capture reactions of a fast beam of C₂H₅⁺ with a series of metal target atoms (K, Na, Ca, Mg, and Zn) have been investigated by neutral beam scattering techniques. Reactions of C₂H₅⁺ with Mg or Zn atoms lead to formation of ground state radicals and an excited state about 0.5 eV above the dissociation limit of C₂H₄+H. Analysis of branching ratios for these processes over a range of Mg atom densities shows that the ion beam is a mixture of two isomers in the ratio of about 7.3/1.0 for beams generated either by electron impact or chemical ionization methods. From neutral-precursor ion relationships we propose that the major and minor components of the ion beam are the bridged and classical C₂H ₅⁺ structures, respectively. Analysis of neutral beam profiles in experiments with Na or K targets indicate the formation of a dissociative state of the classical radical lying about 4.2 eV above the ground state. An upper limit of 2.2 eV to the barrier to 1, 2 hydrogen migration in the classical radical is provided by the energy of the lowest state of the bridged radical observed.