title: Ab initio and density functional theory (DFT) studies on triflic acid with water and protonated water clusters.
abstract: The structure, stability and infrared spectral signatures of triflic acid (TA) with water clusters (Wn) and protonated water clusters (TAH+Wn, n = 1 - 6) were computed using DFT and MP2 methods. Our calculations show that a minimum of three water molecules are necessary to stabilize the dissociated zwitterionic form of TA. It can be seen from the results that there is no significant movement of protons in smaller (n = 1 and 2) and linear (n = 1 - 6) types of water clusters. Further, the geometries of TAWnclusters first form a neutral pair (NP) to contact ion pair (CIP), then form a solvent separated ion pair (SSIP) in a water hexamer. These findings reveal that proton transfer may take place through NP to CIP and then CIP to SSIP. The calculated binding energies (BEs) of ion pair clusters is always higher than that of NP clusters (i.e., more stable than the NP). Existing excess proton linear chain clusters transfer a proton to adjacent water molecules via a Grotthuss mechanism, whereas the same isomers in the branched motifs do not conduct protons. Examination of geometrical parameters and infrared frequencies reveals hydronium ion (H3O+also called Eigen cation) formation in both TAWnand protonated TAWnclusters. The stability of Eigen water clusters is three times higher than that of other non-Eigen water clusters. Our study shows clearly that formation of ion pairs in TAWnand TAH+Wnclusters greatly favors proton transfer to neighboring water molecules and also enhances the stability of these complexes.
authors.affiliation: Department of Chemistry and Research Institute, SRM University, Kattankulathur, 603203, Tamil Nadu, India.|Chemical Laboratory, CSIR-Central Leather Research Institute, Adyar, Chennai, 600 020, India.
authors.forename: M
authors.identifier: http://orcid.org/0000-0002-1886-7708
authors.initials: M
authors.lastname: Prakash
authors.affiliation: Chemical Laboratory, CSIR-Central Leather Research Institute, Adyar, Chennai, 600 020, India. subbu@clri.res.in.|Academy of Scientific and Innovative Research (AcSIR), CSIR-CLRI Campus, Chennai, 600 020, India. subbu@clri.res.in.
authors.forename: V
authors.initials: V
authors.lastname: Subramanian
keywords: Ab initio; DFT; H-bonds; Ion pairs; Water and protonated water clusters