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In this paper, for the hydrogen abstraction reaction of HCHO by OH radicals assisted by water, formic acid, or sulfur acid, the possible reaction mechanisms and kinetics have been investigated theoretically using quantum chemistry methods and transition-state theory. The potential energy surfaces calculated at the CCSD(T)/6-311++G(df,pd)//MP2(full)/6-311++G(df,pd) levels of theory reveal that, due to the formation of strong hydrogen bond(s), the relative energies of the transition states involving catalyst are significantly reduced compared to that reaction without catalyst. However, the kinetics calculations show that the rate constants are smaller by about 3, 9, or 10 orders of magnitude for water, formic acid, or sulfur acid assisted reactions than that uncatalyzed reaction, respectively. Consequently, none of the water, formic acid, or sulfur acid can accelerate the title reaction in the atmosphere.

ABSTRACT:The hydrogen bonding complexes formed between the H 2 O and OH radical have been completely investigated for the first time in this study using density functional theory (DFT). A larger basis set 6-311ϩϩG(2d,2p) has been employed in conjunction with a hybrid density functional method, namely, UB3LYP/6-311ϩϩG(2d,2p). The two degenerate components of the OH radical 2 ⌸ ground electronic state give rise to independent states upon interaction with the water molecule, with hydrogen bonding occurring between the oxygen atom of H 2 O and the hydrogen atom of the OH radical. Another hydrogen bond occurs between one of the H atoms of H 2 O and the O atom of the OH radical. The extensive calculation reveals that there is still more hydrogen bonding form found first in this investigation, in which two or three hydrogen bonds occur at the same time. The optimized geometry parameter and interaction energy for various isomers at the present level of theory was estimated. The infrared (IR) spectrum frequencies, IR intensities, and vibrational frequency shifts are reported. The estimates of the H 2 O ⅐ OH complex's vibrational modes and predicted IR spectra for these structures are also made. It should be noted that a total of 10 stationary points have been confirmed to be genuine minima and transition states on the potential energy hypersurface of the H 2 O ⅐ HO system. Among them, four genuine minima were located.

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A surprising switch of the protonated site from methanol to water in protonated methanol-water mixed clusters, H(+)(MeOH)(m)(H(2)O)(1) (m = 1-9), was investigated by a joint theoretical and vibrational spectroscopic study. Extensive density functional calculations on all possible structural isomers revealed that the switch of the ion core is correlated with the size dependence and structural development of the hydrogen-bond network: (1) the CH(3)OH(2)(+) ion core is preferred for the small-sized clusters of m = 1 and 2, (2) coexistence of the H(3)O(+) and CH(3)OH(2)(+) ion cores is highly plausible for 3 < or = m < or = 7 clusters, and (3) obvious preference of the H(3)O(+) ion core appears from m > or = 8 with the appearance of the characteristic "tricyclic" structure of the hydrogen-bond network. The ion core switch at m approximately 8 is experimentally supported by the infrared photodissociation spectra of the size-selected clusters and the size dependence of the fragmentation channel following vibrational excitation.