Probing the interaction between the encapsulated water molecule and the fullerene cages in H2O@C60− and H2O@C59N−

Abstract

We report a high-resolution photoelectron imaging study of cryogenically-cooled H₂O@C₆₀⁻ and H₂O@C₅₉N⁻ endohedral fullerene anions. The electron affinity (EA) of H₂O@C₆₀ is measured to be 2.6923 ± 0.0008 eV, which is 0.0088 eV higher than the EA of C₆₀, while the EA of H₂O@C₅₉N is measured to be 3.0058 eV ± 0.0007 eV, which is 0.0092 eV lower than the EA of C₅₉N. The opposite shifts are found to be due to the different electrostatic interactions between the encapsulated water molecule and the fullerene cages in the two systems. There is a net coulombic attraction between the guest and host in H₂O@C₆₀⁻, but a repulsive interaction in H₂O@C₅₉N⁻. We have also observed low-frequency features in the photoelectron spectra tentatively attributed to the hindered rotational excitations of the encapsulated H₂O molecule, providing further insights into the guest–host interactions in H₂O@C₆₀⁻ and H₂O@C₅₉N⁻.