Gas-phase experimental and theoretical studies of adenine, imidazole, pyrrole, and water non-covalent complexes

We present both experimental and theoretical gas-phase studies of several n oncovalent complexes of elementary molecules of biological interest: adenin e, imidazole, pyrrole, and water. By means of charge-transfer collisions be tween those complexes and laser-excited atoms, dipole-bound cluster anions are observed. This Rydberg electron transfer (RET) spectroscopic technique is used to experimentally determine the very weak excess electron binding e nergies of the complex anions. Theoretical calculations which rely on a hom emade semiempirical intermolecular force field allow far the determination of the structures of the low-lying equilibrium configurations of the neutra l complexes. The electrostatic properties of these configurations (dipole m oments, quadrupole moments, etc.) lead to predicted excess electron binding energies which are compared to the experimental values. This comparison pr ovides a test of the validity of the employed methods, as discussed in the case of the five studied complexes: adenine-imidazole, adenine-pyrrole, ade nine-water, pyrrole-water, and imidazole-water.