The adsorptive interactions of 2-propanol (2-PrOH) molecules with silica surfaces were investigated using ab initio and density functional calculations. Two cluster models of silica were chosen to represent the terminal ≡SiOH groups and the siloxane bridges ≡Si-(O) 2-Si≡ on the silica surface. The Hartree-Fock (HF) and Density Functional Theory (DFT) approaches, employing a 6-31G(d) basis set, were used to calculate the geometries, electronic structures, vibrational frequencies and adsorption energies of the adsorption complexes formed. The calculated adsorption energies were corrected for zero-point vibrational energies (ZPVE) and basis set superposition errors (BSSE). The results favoured a most likely surface configuration for the physisorbed species in which 2-PrOH molecules are bound to exposed silanol groups via two hydrogen bonds, with the alcoholic-OH group acting simultaneously as a proton acceptor and donor. Moreover, bonding of 2-PrOH with strained surface siloxane bridges (≡Si-O-Si≡) was shown to lead to chemisorption of the alcohol molecule. These findings have been shown to help interpreting reported infrared spectroscopic results of in-situ experimental studies.
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