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

Abstract

In this work, we present infrared (IR) spectra of H7O3(+) and its deuterium isotopomers calculated by direct molecular dynamics (MD) simulations at the B3LYP/6-31+G** computational level. The calculated spectra obtained at 100, 300, and 500 K were compared to available experimental observations, and spectral features were assigned using normal-mode analysis (NMA) and driven molecular dynamics (DMD). Spectral peaks at 2410 and 2540 cm(-1) were assigned to asymmetric and symmetric 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 asymmetric 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-resolution spectrum obtained by Schwarz at 2200-2300 cm(-1) [Schwarz, H. A. J. Chem. Phys. 1977, 67, 5525-5534] and vibrational predissociation spectrum by Lee et al. ∼2300 cm(-1) [Okumura, M.; Yeh, L. I.; Myers, J. D.; Lee, Y. T. J. Chem. Phys. 1990, 94, 3416-3427].