Exploring the Properties of H2O@C_(60)with the Local Second-Order Moller-Plesset Perturbation Theory:Blue or Red Shift in C_(60)and H2O Fundamentals to Expect?

摘要

The main structural, energetic and vibrational properties of H2O@C_(60)were computationally investigated using the densityfitting local second-order Moller-Plesset(DF-LMP2)theory. Two low-energy isomers, of C2 and C1 symmetry, were initially considered and only the latter one was identified as a true minimum with the lowest energy. The energy difference between these isomers was rather small(only 0.002 kcal/mol)and the respective interaction energy of any of the H2O@C_(60)isomers was ~(-1)4.26 kcal/mol. These isomers were structurally similar having larger values of O-H bond lengths and angles by 0.0082 A and 0.9 degrees, respectively, compared to a free water molecule. The calculated harmonic IR spectrum of the C1 isomer was characterized by:a)the presence of water frustrated translation frequencies at 90.5-94.3 cm~(-1);b)the red shift in frequency of the first radial C_(60)mode(by-(1.8-2.7)cm~(-1))and the blue shift for the other three IRactive C_(60)modes(by up to 2.2 cm~(-1));c)the red shift in H2O fundamentals by-9.2,-10.4 and-123.8 cm~(-1)for the bending, symmetric and antisymmetric mode, respectively, in excellent agreement with recently reported experimental results. The zero-point energy contributed only 0.15 kcal/mol to the ZPE-corrected value of H2O@C_(60)interaction energy which became now equal to-14.11 kcal/mol.