Theoretical structures of triflic acid-water clusters and the molecular mechanism of proton dissociation

Structural and energetic information required for recently proposed quasichemical theories of solution chemistry have been obtained for clusters of water with triflic acid, CF3SO3H(H2O)(n) for n=1-6. Quantum mechanical calculations on the clusters indicate that the acid proton does not dissociate with n=1 or 2 hydrating water molecules, but does dissociate for n greater than or equal to 3 water molecule partners. The computed minimum energy structures indicate that both "Eigen" (H9O4+) (n=3,4,6) and "Zundel" (H5O2+) (n=5) structures are likely to play a role in the molecular mechanism of acid dissociation in Nafion(R).