Project Title
Academic department under which the project should be listed
CSM - Chemistry and Biochemistry
Research Mentor 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 study of H/D isotope effects can provide useful information on a proton’s location inside a non-linear pathway. In C2O4H–, a normal mode analysis was performed at the MP2/aug-cc-pVDZ and B3LYP/aug-cc-pVDZ levels of theory. Previous experimental studies suggest a frequency shift ~1000 cm-1 for the OH stretch mode upon the H/D isotopic substitution. Isotope calculations resulted in a shift of 842 cm-1 at the B3LYP/aug-cc-pVDZ level of theory. 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. The harmonic frequency of the OH in-plane bending mode in the hydrogen oxalate is 1441 cm-1 at the MP2/aug-cc-pVDZ level of theory. We have located the transition state for the proton transfer between two oxygens in the hydrogen oxalate. The imaginary frequency for this vibration is 1055i cm-1 at the B3LYP/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 due to mode coupling.
KEYWORDS Proton transfer, hydrogen-bonding interaction, normal mode analysis, combination bands, isotopic substitution, anharmonicity.
Disciplines
Chemistry | Physical Chemistry
Included in
Model Calculations of H/D Isotope Substitution in Hydrogen Oxalate Anion Using the Normal Mode Analysis
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 study of H/D isotope effects can provide useful information on a proton’s location inside a non-linear pathway. In C2O4H–, a normal mode analysis was performed at the MP2/aug-cc-pVDZ and B3LYP/aug-cc-pVDZ levels of theory. Previous experimental studies suggest a frequency shift ~1000 cm-1 for the OH stretch mode upon the H/D isotopic substitution. Isotope calculations resulted in a shift of 842 cm-1 at the B3LYP/aug-cc-pVDZ level of theory. 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. The harmonic frequency of the OH in-plane bending mode in the hydrogen oxalate is 1441 cm-1 at the MP2/aug-cc-pVDZ level of theory. We have located the transition state for the proton transfer between two oxygens in the hydrogen oxalate. The imaginary frequency for this vibration is 1055i cm-1 at the B3LYP/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 due to mode coupling.
KEYWORDS Proton transfer, hydrogen-bonding interaction, normal mode analysis, combination bands, isotopic substitution, anharmonicity.