Academic department under which the project should be listed

CSM - Chemistry and Biochemistry

Faculty Sponsor Name

Martina Kaledin

Abstract (300 words maximum)

In this computational chemistry work, we describe ab initio calculations and assignment of infrared (IR) spectra of an intramolecular H-bonding system hydrogen oxalate, C2O4H. The mechanism and dynamics of proton transfer are of fundamental importance in chemistry and biology. In C2O4H, proton transfer occurs along the non-linear path. Previous experimental studies are signaling very strong coupling between OH stretch mode and low frequency motions. We calculated IR spectra at 300 K using the direct molecular dynamics (MD) method at the MP2/ aug-cc-pVDZ level of theory and assigned the prominent spectral features using the driven MD (DMD) method. The DMD method uses a sinusoidal electric field as a driving force to assist analyzing the complex anharmonic features exhibited by hydrogen oxalate anion. The barrier height for the proton transfer is 2.93 kcal/mol at the MP2/aug-cc-pVDZ level of theory. The low energy barrier for the proton transfer and hydrogen bonding interactions complicates the IR spectrum proton stretching region for hydrogen oxalate. The O-H stretch and bending modes are expected to undergo an anharmonic shift. As a result, the proton transfer absorption bands broadened over 2800 - 3200 cm-1 range. Based on DMD simulations, we found that the in-plane O-H bending mode shifted to ~1390 cm-1, in excellent agreement with experimental values, while the harmonic frequency is 1441 cm-1 at the MP2/aug-cc-pVDZ level of theory. While the in-plane bending mode and O-H stretching mode are reported to dominate the proton transfer, our calculations indicate that the proton transfer can easily occur as a result of mode coupling. The analysis of DMD trajectories provides atomic level insights into the proton transfer motion.

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Investigating the Proton Transfer Dynamics and Vibrational Spectrum of Hydrogen Oxalate using Driven Molecular Dynamics Simulations

In this computational chemistry work, we describe ab initio calculations and assignment of infrared (IR) spectra of an intramolecular H-bonding system hydrogen oxalate, C2O4H. The mechanism and dynamics of proton transfer are of fundamental importance in chemistry and biology. In C2O4H, proton transfer occurs along the non-linear path. Previous experimental studies are signaling very strong coupling between OH stretch mode and low frequency motions. We calculated IR spectra at 300 K using the direct molecular dynamics (MD) method at the MP2/ aug-cc-pVDZ level of theory and assigned the prominent spectral features using the driven MD (DMD) method. The DMD method uses a sinusoidal electric field as a driving force to assist analyzing the complex anharmonic features exhibited by hydrogen oxalate anion. The barrier height for the proton transfer is 2.93 kcal/mol at the MP2/aug-cc-pVDZ level of theory. The low energy barrier for the proton transfer and hydrogen bonding interactions complicates the IR spectrum proton stretching region for hydrogen oxalate. The O-H stretch and bending modes are expected to undergo an anharmonic shift. As a result, the proton transfer absorption bands broadened over 2800 - 3200 cm-1 range. Based on DMD simulations, we found that the in-plane O-H bending mode shifted to ~1390 cm-1, in excellent agreement with experimental values, while the harmonic frequency is 1441 cm-1 at the MP2/aug-cc-pVDZ level of theory. While the in-plane bending mode and O-H stretching mode are reported to dominate the proton transfer, our calculations indicate that the proton transfer can easily occur as a result of mode coupling. The analysis of DMD trajectories provides atomic level insights into the proton transfer motion.