Characterizing the Vibrational Spectra of Hydrogen Bonded Systems with Molecular Dynamics Simulations and Quantum Chemical Methods
Date of Award
Master of Science in Chemical Sciences (MSCB)
We apply and assess the utility of DMD for the purpose of investigating complex spectral features in N2H+···OC, N2D+···OC, C2O4H-, C2O4D- and (HCOOH)2. The proton transfer as a vibrational motion consists of diffuse qualities that can be accounted for with classical and quantum chemical analyses. Classical approaches yield a wealth of information about vibrational spectra at a reduced cost, as in the case of previously investigated N4H+. The isoelectronic N2H+···OC has a smaller dipole moment than N4H+ and a calculated DMD parallel H+ transfer frequency of 1800 cm-1, disagreeing with the VCI (1541 cm-1) and VPT2 (1620 cm-1) values. However, the perpendicular H+ bending mode is evaluated at 910 cm-1, in good agreement with VCI (954 cm-1). Combination bands were recovered at 980 and 1980 cm-1, with weaker absorptions featured at 450 and 380 cm-1. In C2O4H-, the O-H stretch DMD value was in good agreement with the experiment. The brightest experimental peak in the O-H stretching region was ωmax= 2945 cm-1, while the DMD value for the motion was ν1 = 3000 cm-1. C2O4H- combination bands were characterized at 800-850, 1505, and 1450 cm-1 were assigned using the analysis of the atomic motion along the trajectory. Rudimentary explicit solvation effects were explored for C2O4H- and Coupled Cluster PES scans were performed to support all results. A combination band of O-H and C-H in-plane bending was found in the H+ transfer region for (HCOOH)2 using the 2D-IR DMD procedure.
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