Calculations of the infrared and Raman spectra of simple thiols and thiol–water complexes

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Abstract

The frequencies and intensities of infrared and Raman spectra of H2S, CH3SH, CH3CH2SH, and CH2[DOUBLE BOND]CHCH2SH, isolated and complexed with one water molecule acting as a proton acceptor were calculated at the ab initio and density functional level. Hartree-Fock, MP2 and CCSD(T) methods were used both for the geometry optimization and spectra calculations at the molecular orbital level. The B3LYP, PBE0, and M06 exchange-correlation potentials were employed to calculate the same properties at the DFT level. Both Pople basis sets, 6-31+G(d) and 6-311++G(3df,2pd), and Dunning basis sets, aug-cc-pVTZ and aug-cc-pVQZ, were used. SH and CS frequency shifts upon water complexation were studied, and a discussion is performed on the expected relation between the CH and CS Raman activities, in view of their usefulness for studies in protein chemistry. Scaling factors for the vibrational frequencies were obtained for all the combination of methods and basis sets, and shown to be completely similar to the ones present in the literature when available. Scaling factors for the M06 method are presented for the first time with these basis sets. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010

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