An excess electron bound to urea. I. Canonical and zwitterionic tautomers

The possibility of electron binding to urea was studied at the coupled clus ter level of theory with single, double, and noniterative triple excitation s. It was found that none of the urea isomers forms a valence anionic state although almost all of them can attach an excess electron and form a stabl e dipole-bound or Rydberg anion. Moreover, the canonical tautomers are the lowest energy structures of the neutral and anion. The zwitterionic isomer was found to be locally stable only when solvated with an "extra" electron and the corresponding anion is a Rydberg species perturbed by a neighboring negative charge. (C) 2001 American Institute of Physics.