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H 2 O inside the fullerene C 60 : Inelastic neutron scattering spectrum from rigorous quantum calculations

https://doi.org/10.1063/5.0086842

Xu, Minzhong ; Felker, Peter M. ; Bačić, Zlatko ( March 2022 , The Journal of Chemical Physics)

We present a methodology that, for the first time, allows rigorous quantum calculation of the inelastic neutron scattering (INS) spectra of a triatomic molecule in a nanoscale cavity, in this case, H₂O inside the fullerene C₆₀. Both moieties are taken to be rigid. Our treatment incorporates the quantum six-dimensional translation–rotation (TR) wave functions of the encapsulated H₂O, which serve as the spatial parts of the initial and final states of the INS transitions. As a result, the simulated INS spectra reflect the coupled TR dynamics of the nanoconfined guest molecule. They also exhibit the features arising from symmetry breaking observed for solid H₂O@C₆₀at low temperatures. Utilizing this methodology, we compute the INS spectra of H₂O@C₆₀for two incident neutron wavelengths and compare them with the corresponding experimental spectra. Good overall agreement is found, and the calculated spectra provide valuable additional insights.