Deprotonated Dicarboxylic Acid Homodimers: Hydrogen Bonds and Atmospheric Implications

Abstract

Dicarboxylic acids represent an important class of water-soluble organic compounds found in the atmosphere. In this work we are studying properties of dicarboxylic acid homodimer complexes (HO2C(CH2)nCO2(-)[HO2C(CH2)nCO2H], n = 0-12), as potentially important intermediates in aerosol formation processes. Our approach is based on experimental data from negative ion photoelectron spectra of the dimer complexes combined with updated measurements of the corresponding monomer species. These results are analyzed with quantum-mechanical calculations, which provide further information about equilibrium structures, thermochemical parameters associated with the complex formation, and evaporation rates. We find that upon formation of the dimer complexes the electron binding energies increase by 1.3-1.7 eV (30.0-39.2 kcal/mol), indicating increased stability of the dimerized complexes. Calculations indicate that these dimer complexes are characterized by the presence of strong intermolecular hydrogen bonds with high binding energies and are thermodynamically favorable to form with low evaporation rates. Comparison with the previously studied HSO4(-)[HO2C(CH2)2CO2H] complex (J. Phys. Chem. Lett. 2013, 4, 779-785) shows that HO2C(CH2)2CO2(-)[HO2C(CH2)2CO2H] has very similar thermochemical properties. These results imply that dicarboxylic acids not only can contribute to the heterogeneous complexes formation involving sulfuric acid and dicarboxylic acids but also can promote the formation of homogeneous complexes by involving dicarboxylic acids themselves.

Direct Observation of Hierarchic Molecular Interactions Critical to Biogenic Aerosol Formation

“…• clustering with the organic compound, well reflecting the lower limits of the intermolecular binding or interaction strength in the anionic clusters ( Supplementary Figure 3) 17,29 . Thus, the larger the ΔEBE is, the stronger intermolecular binding of the organics with bisulfate in the corresponding anionic clusters will be.…”

“…Quantum chemical calculations were performed using the NWChem program suite 45 . We have shown previously that the combination of structure optimization using the B3LYP functional followed by single-point energy calculations using the M06-2× functional can give good agreement between calculations and experiments for the atmospheric pre-nucleation clusters 25,29 . Thus we employed the same theoretical approach in this work.…”

Sulfuric acid and aromatic carboxylate clusters H2SO4·ArCOO−: Structures, properties, and their relevance to the initial aerosol nucleation

“…This combination of the B3LYP structural optimization followed by the M06-2X single-point energy calculations has previously been shown to give good agreement between theory and experiment. [30,31,34] In addition, we also tested the accuracy of DFT calculated energies by performing CCSD(T) single point energy calculations on H 2 SO 4 /benzoic and H 2 SO 4 /m-toluic acid systems. It was found that the M06-2X calculated relative stabilities and binding energies are in good agreement with the CCSD(T) results.…”

“…[8] We have been interested in characterizing the small pre-nucleation clusters relevant to NPF, especially organic acid containing clusters, by combining negative ion photoelectron spectroscopy (NIPES) and quantum chemical calculations. [30][31][32][33][34][35][36][37] For example, we have shown that succinic acid molecule, HO 2 C(CH 2 ) 2 CO 2 H, is capable of stabilizing the bisulfate ion HSO 4 − and its own conjugate base succinate ion, HO 2 C(CH 2 ) 2 CO 2 − , indicating significant thermodynamic advantage of organic molecules in promoting bisulfate clusters and organic aerosol particles formation. [30,34] Most recently, we have studied the deprotonated sulfuric acid-formic acid anionic cluster [H 2 SO 4 •HCOOH−H + ] − , and found that the charge delocalization accompanying formation of two strong hydrogen bonds is strong enough to compensate the proton affinity imbalance in forming H 2 SO 4 •HCOO − cluster.…”

“…[30][31][32][33][34][35][36][37] For example, we have shown that succinic acid molecule, HO 2 C(CH 2 ) 2 CO 2 H, is capable of stabilizing the bisulfate ion HSO 4 − and its own conjugate base succinate ion, HO 2 C(CH 2 ) 2 CO 2 − , indicating significant thermodynamic advantage of organic molecules in promoting bisulfate clusters and organic aerosol particles formation. [30,34] Most recently, we have studied the deprotonated sulfuric acid-formic acid anionic cluster [H 2 SO 4 •HCOOH−H + ] − , and found that the charge delocalization accompanying formation of two strong hydrogen bonds is strong enough to compensate the proton affinity imbalance in forming H 2 SO 4 •HCOO − cluster. [38,39] In this work, we focus on the clusters formed between bisulfate ion and series of aromatic volatile organic compounds (VOCs), including benzoic and toluic acids.…”