Observation of the dipole- and quadrupole-bound anions of 1,4-dicyanocyclohexane.

Quadrupole-bound anions are negative ions in which their excess electrons are loosely bound by long-range electron-quadrupole attractions. Experimental evidence for quadrupole-bound anions has been scarce; until now, only trans-succinonitrile had been experimentally confirmed to form a quadrupole-bound anion. In this study, we present experimental evidence for a new quadrupole-bound anion. Our combined Rydberg electron transfer/anion photoelectron spectroscopy study demonstrates that the ee conformer of 1,4-dicyanocyclohexane (DCCH) supports a quadrupole-bound anion state, and that the cis-DCCH conformer forms a dipole-bound anion state. The electron binding energies of the quadrupole- and dipole-bound anions are measured as 18 and 115 meV, respectively, both of which are in excellent agreement with theoretical calculations by Sommerfeld.