Disciplines
Chemistry | Physical Chemistry
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.
Academic department under which the project should be listed
CSM - Chemistry and Biochemistry
Primary Investigator (PI) Name
Martina Kaledin
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.