Stable isomers for trifluoroacetic acid (TFA) pentahydrates obtained from density functional calculations

Stable isomers of trifluoroacetic acid (TFA) pentahydrate clusters, TFA-(H2O)5, have been explored by using density functional theory calculations. As done for TFA-(H2O)4 (Ito, 2013), structure optimization and vibrational calculations were performed for 70 isomeric structures (68 for neutral and 2 for ion-pair species, respectively) at the B971/6-311++G(3df,3pd) level. We found that the edge-sharing bicyclic isomer is at the global minimum and that three other isomers lie energetically within 100 cm−1. Two types of ion-pair species were found to be unstable by 1100 cm−1 in comparison with the global minimum. The results were compared with infrared spectra observed in nitrogen matrix.