Computational study of hydrogen-bonded complexes of HOCO with acids: HOCO⋯HCOOH, HOCO⋯H2SO4, and HOCO⋯H2CO3

• Published in: The Journal of Chemical Physics
• Main Authors: Hazra, Montu K., Francisco, Joseph S., Sinha, Amitabha
• Other Authors: National Science Foundation
• Format: Article in Journal/Newspaper
• Language: English
• Published: AIP Publishing 2012
• Subjects: Physical and Theoretical Chemistry; General Physics and Astronomy; Zero Point; Carbonic acid
• Online Access: http://dx.doi.org/10.1063/1.4742817; https://pubs.aip.org/aip/jcp/article-pdf/doi/10.1063/1.4742817/14081318/064319_1_online.pdf

Quantum chemistry calculations at the density functional theory (DFT) (B3LYP), MP2, QCISD, QCISD(T), and CCSD(T) levels in conjunction with 6-311++G(2d,2p) and 6-311++G(2df,2p) basis sets have been performed to explore the binding energies of open-shell hydrogen bonded complexes formed between the HOCO radical (both cis-HOCO and trans-HOCO) and trans-HCOOH (formic acid), H2SO4 (sulfuric acid), and cis-cis-H2CO3 (carbonic acid). Calculations at the CCSD(T)/6-311++G(2df,2p) level predict that these open-shell complexes have relatively large binding energies ranging between 9.4 to 13.5 kcal/mol and that cis-HOCO (cH) binds more strongly compared to trans-HOCO in these complexes. The zero-point-energy-corrected binding strengths of the cH⋯Acid complexes are comparable to that of the formic acid homodimer complex (∼13–14 kcal/mol). Infrared fundamental frequencies and intensities of the complexes are computed within the harmonic approximation. Infrared spectroscopy is suggested as a potential useful tool for detection of these HOCO⋯Acid complexes in the laboratory as well as in various planetary atmospheres since complex formation is found to induce large frequency shifts and intensity enhancement of the H-bonded OH stretching fundamental relative to that of the corresponding parent monomers. Finally, the ability of an acid molecule such as formic acid to catalyze the inter-conversion between the cis- and trans-HOCO isomers in the gas phase is also discussed.