Xing-Feng Tan

Theoretical studies on reactions of the stabilized H2COO with HO2 and the HO2···H2O complex.

The reactions of H(2)COO with HO(2) and the HO(2)···H(2)O complex are studied by employing the high-level quantum chemical calculations with B3LYP and CCSD(T) theoretical methods, the conventional transition-state theory (CTST), and the Rice-Ramsperger-Kassel-Marcus (RRKM) with Eckart tunneling correction. The calculated results show that the proton transfer plus the addition reaction channel (TS1A) is preferable for the reaction of H(2)COO with HO(2) because the barriers are -10.8 and 1.6 kcal/mol relative to the free reactants and the prereactive complex, respectively, at the CCSD(T)/6-311++G(3df,2p)//B3LYP/6-311++G(d,p) level of theory. Furthermore, the rate constant via TS1A (2.23 × 10(-10) cm(3) molecule(-1) s(-1)) combined with the concentrations of the species in the atmosphere demonstrates that the HO(2) radical would be the dominant sink of H(2)COO in some areas, where the concentration of water is less than 10(17) molecules cm(-3). In addition, although the single water molecule would lower the activated barrier of TS1A from 1.0 to 0.1 kcal/mol with respect to the respective complexes, the rate constant is lower than that of the reaction of HO(2) with H(2)COO.

Theoretical Study on the Gas Phase Reaction of Sulfuric Acid with Hydroxyl Radical in the Presence of Water

The reactions of H2SO4 with the OH radical without water and with water are investigated employing the quantum chemical calculations at the B3LYP/6-311+G(2df,2p) and MP2/aug-cc-pv(T+d)z levels of theory, respectively. The calculated results show that the reaction of H2SO4 with OH and H2O is a very complex mechanism because of the formation of the prereactive complex prior to the transition state and product. There are two prereactive complexes with stabilization energies being -20.28 and -20.67 kcal/mol, respectively. In addition, the single water can lower the energy barriers of the hydrogen abstraction and the proton transfer to 7.51 and 6.37 kcal/mol, respectively from 13.79 and 8.82 kcal/mol with respect to the corresponding prereactive complex. The computed rate constants indicate that the water-assisted reaction of sulfuric acid with OH radical is of greater importance than the reaction of the naked sulfuric acid with the OH radical because the rate constant of the water-assisted process is about 10(3) faster than that of the reaction sulfuric acid with OH. Therefore, the conclusion is obtained that the water-assisted process plays an important role in the sink for the gaseous sulfuric acid in the clean area.

Theoretical studies on gas-phase reactions of sulfuric acid catalyzed hydrolysis of formaldehyde and formaldehyde with sulfuric acid and H2SO4···H2O complex.

The gas-phase reactions of sulfuric acid catalyzed hydrolysis of formaldehyde and formaldehyde with sulfuric acid and H2SO4···H2O complex are investigated employing the high-level quantum chemical calculations with M06-2X and CCSD(T) theoretical methods and the conventional transition state theory (CTST) with Eckart tunneling correction. The calculated results show that the energy barrier of hydrolysis of formaldehyde in gas phase is lowered to 6.09 kcal/mol from 38.04 kcal/mol, when the sulfuric acid is acted as a catalyst at the CCSD(T)/aug-cc-pv(T+d)z//M06-2X/6-311++G(3df,3pd) level of theory. Furthermore, the rate constant of the sulfuric acid catalyzed hydrolysis of formaldehyde combined with the concentrations of the species in the atmosphere demonstrates that the gas-phase hydrolysis of formaldehyde of sulfuric acid catalyst is feasible and could be of great importance for the sink of formaldehyde, which is in previously forbidden hydrolysis reaction. However, it is shown that the gas-phase reactions of formaldehyde with sulfuric acid and H2SO4···H2O complex lead to the formation of H2C(OH)OSO3H, which is of minor importance in the atmosphere.

New insights in atmospheric acid-catalyzed gas phase hydrolysis of formaldehyde: a theoretical study

The gas phase hydrolysis of HCHO catalyzed via nitric acid and acetic acid, the typical atmospheric acids has been theoretically investigated using M06-2X, CCSD(T), and CCSD(T)-F12A theoretical methods using the 6-311++G(d,p), aug-cc-pVTZ, and VTZ-F12 basis sets and utilizing transition state theory. Our studies predict that when the HNO3 or CH3COOH and HCHO⋯H2O act as reactants, the reactions occur in one step, whereas the reactions of HNO3⋯H2O or CH3COOH⋯H2O with HCHO proceed via a two-step mechanism. Our results also show that the free energy barrier of the gas phase hydrolysis of HCHO assisted by HNO3 or CH3COOH is reduced to 13.95 or 14.27 kcal mol−1 relative to the respective pre-reactive complex from 40.23 kcal mol−1 in the naked HCHO + H2O reaction. The calculated kinetic data suggests that the HCHO + HNO3⋯H2O entrance channel with a two-step mechanism is 1.84–2.76 times faster than HNO3 + HCHO⋯H2O with a one-step mechanism, whereas the HCHO⋯H2O + CH3COOH entrance path is significantly more favorable than that of HCHO + CH3COOH⋯H2O, in the temperature range of 200–300 K. The reaction rates of the gas phase hydrolysis of HCHO catalyzed by HNO3 or CH3COOH are much slower than that of the gas phase reaction of HCHO with an OH radical, which demonstrates that the contributions of both catalytic reactions are of minor importance for the sink of HCHO in gas-phase atmospheric chemistry. However, the new findings in this investigation are not only of great necessity and importance for elucidating the gas phase hydrolysis of formaldehyde, but are also of great interest for understanding the importance of other carbonyl compounds in the atmosphere.