Path integral Monte Carlo(PIMC)method is employed to study the thermal properties of the X@C_(50)[X=H_(2),He,Ne,Ar]system at temperatures from 5 K to 300 K.The interaction energies and probability distribution functions of one noble gas atom or H_(2) inside D5h-symmetry C_(50) are obtained.A rough sphere model is used in calculating interaction energies,as a comparison.This model gives much lower interaction energy than PIMC calculations on all X@C_(50),except He@C_(50).The PIMC method and the sphere model get nearly the same values of interaction energies on He@C_(50).The spatial distributions are enlarged by the increase in temperature,while the interaction energies change slowly in a wide range of temperature.Temperature is not the major reason for the stability of the system.It is impossible to trap an X atom into C_(50),except H_(2) because only the H_(2)@C_(50) has positive interaction energies from the PIMC calculations.
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