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-.
Highlights
One of the most interesting questions about H2O@C60 concerned the nature of the guest–host interactions of the water molecule trapped in the C60 cage
These studies revealed a splitting of the ground rotational state of ortho-H2O and a symmetry-breaking of the C60 cage, indicating a quadrupolar interaction between H2O and C60.30 In addition, the dipole moment of H2O@C60 was measured to be around 0.5 D,25,26 in good agreement with theoretical calculations.[20,21,22,23,24]
We present a high-resolution photoelectron (PE) imaging study of the H2O@C60À and H2O@C59NÀ anions cooled in a cryogenic ion trap
Summary
C60 and H2O@C60, suggesting that the water molecule has very weak interactions with the cage.[14]. H2O@C60 were studied by inelastic neutron scattering, farinfrared spectroscopy, and nuclear magnetic resonance.[27,28,29]. These studies revealed a splitting of the ground rotational state of ortho-H2O and a symmetry-breaking of the C60 cage, indicating a quadrupolar interaction between H2O and C60.30 In addition, the dipole moment of H2O@C60 was measured to be around 0.5 D,25,26 in good agreement with theoretical calculations.[20,21,22,23,24] The signi cant reduction of the dipole moment of the encapsulated H2O is a result of the strong shielding effect by the nonpolar C60 cage. Low-frequency features in the PE spectra are observed and tentatively attributed to the hindered rotational excitations[30] of the encapsulated H2O molecule, providing further insights into the guest–host interactions in H2O@C60À and H2O@C59NÀ
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