Vibrational Spectroscopy and Proton Transfer Dynamics in Protonated Oxalate

Abstract

The dynamics and infrared spectroscopic signatures of proton transfer in protonated oxalate (p-Oxa) are studied using classical and quantum dynamics. The intermolecular interactions are described by a force field suitable to follow proton transfer. This allows to carry out multiple extended classical molecular dynamics (MD) and ring polymer MD simulations from which the infrared spectrum is determined. Simulations at 600 K sample the quantum mechanical ground state probability distribution and best reproduce the experimentally observed maximum absorption wavelength and part of the line shape. Comparison with the experimentally measured spectrum provides an estimate for the barrier height for proton transfer which can not be determined directly from experiment. A barrier of 4.2 kcal/mol is found to best reproduce the position and width of the infrared absorption of the transferring proton in p-Oxa and also leads to an infrared (IR) spectrum in good agreement with experiment for the deuterated species d-Oxa. A novel means to capture the two resonance forms of oxalate depending on the localization of the excess proton on either CO moiety is found to yield improved results for the spectroscopy in the framework region between 1000 and 2000 cm.

Ultrafast dynamics induced by the interaction of molecules with electromagnetic fields: Several quantum, semiclassical, and classical approaches

“… 198 Conversely, for protonated oxalate, the two resonance forms of the molecule can be parametrized such that the change in bonding character of the CO-subunit (from single. to double-bonded) upon proton transfer is incorporated into the energy function 259 . For both systems (FAD and oxalate), the comparison with experimentally determined infrared spectra in the region of the proton transfer band yields accurate barrier heights of $5–7$ kcal/mol and 4.2 kcal/mol, respectively.…”

“…MMPT with suitably morphed potential energy surfaces was also employed to analyze the gas-phase infrared spectra of formic acid dimer (FAD) 198 and of protonated oxalate 259 . For FAD, a combination of a symmetric double (SDM) and single minimum (SSM) surface yields a realistic description of the double proton transfer potential energy surface (see Fig.…”

Infrared Spectra of Deprotonated Dicarboxylic Acids: IRMPD Spectroscopy and Empirical Valence‐Bond Modeling

“…From the theoretical point of view, proton sharing is a highly anharmonic process causing the failure of static harmonic or even perturbative anharmonic approaches. The dynamics of proton sharing and its influence on vibrational spectroscopy have been investigated by classical and quantum dynamical simulations using reactive potential energy surfaces (PES's) and a more realistic account of anharmonicity …”

“…was used to assign the infrared signature of strong hydrogen bonds in small protonated water clusters based on classical MD simulations . Nuclear quantum effects were further incorporated in MS‐EVB simulations to explain how proton transfer is assisted by multiple weak hydrogen bonds ,…”

“…The dynamics of proton sharing and its influence on vibrational spectroscopy have been investigated by classical and quantum dynamical simulations using reactive potential energy surfaces (PES's) and a more realistic account of anharmonicity. [15][16][17][18][19][20][21][22][23][24][25][26][27][28] First-principles molecular dynamics (MD) methods based on the Born-Oppenheimer (BOMD) or Car-Parrinello (CPMD) schemes employing density-functional theory (DFT) potential and dipole moment surfaces have been used to model proton transfer in organic molecules in the gas phase, e. g. for protonated dialanine [18] or the ðHCO À 3 Þ 2 dimer. [19] In the latter case, nuclear quantum effects were also accounted for within the path-integral framework, owing to their possible importance for describing proton delocalization, especially at low temperatures.…”