VALENCE AND DIPOLE BINDING OF ELECTRONS TO URACIL

Rydberg electron attachment to gas-phase isolated uracil molecules and mixed uracil-argon clusters is examined in a crossing beam experiment . By means of reproducible uracil beam conditions, it is possible to c ontrol the electron-binding process, which is strongly influenced by s olvation. Attachment followed by evaporation of a single argon atom is already sufficient to switch from dipole-bound to valence monomer ura cil anions, as demonstrated by field-detachment measurements. The exis tence of both types of anions is in good agreement with two separate p revious theoretical predictions. A DFT calculation of the valence adia batic electron affinity of uracil provides a small but positive value of 70 meV, close to the measured value of the dipole-bound electron af finity.