Ab Initio Studies of Structural and Vibrational Properties of Protonated Water Cluster H7O3+ and Its Deuterium Isotopologues: An Application of Driven Molecular Dynamics

In this work, we present IR spectra of H7O3+ and its deuterium isotopomers calcd. by direct mol. dynamics (MD) simulations at the B3LYP/6-31+G** computational level. The calcd. spectra obtained at 100, 300, and 500 K were compared to available exptl. observations, and spectral features were assigned using normal-mode anal. (NMA) and driven mol. dynamics (DMD). Spectral peaks at 2410 and 2540 cm-1 were assigned to asym. and sym. stretches of the bridging hydrogen (BH) using NMA. The weak spectral features at 2166 and 2275 cm-1 were assigned to a combination band of BH asym. stretch, H2O in phase wagging, OO stretch, and H3O+ rocking vibrations by DMD simulations. Our observation of BH stretch vibrations as low as 2166 cm-1 is in good agreement with the assignment of the low-resoln. spectrum obtained by Schwarz at (1977) 2200-2300 cm-1 and vibrational predissocn. spectrum by Lee et al. (1990) at ∼2300 cm-1