Theoretical calculation of strong complex formation by the hydroperoxo radical: hydroperoxo.cntdot.water and hydroperoxo.cntdot.ammonia

Abstract

Exploratory ab initio calculations using a minimal basis set support the existence of the 02• 20 and H02• NH3 complexes, as proposed earlier by experiment. For the minimum energy configurations having H02 as the H donor within a linear H-bond structure, electronic stabilization energies of 9.1 and 12.0 kcal/mol are calculated for H02-H20 and HC^-NHb, respectively, compared with 5.3 kcal/mol for (H20)2. Values of AH°a nd AS°for the complex formations are estimated and found consistent with available experimental data. A plausible model is proposed to explain the reactivity of these complexes. These calculations indicate that in the troposphere a significant fraction of the H02 is complexed with H20.

Potential energy surface for the hydroperoxy and water (HO2·H2O) radical complex

“…To make such calculations more practical, stochastic optimizations using classical potential energy functions can be performed ®rst to determine good starting points for the quantum optimizations. [24] performed an ab initio calculation of the HO 2 H 2 O complex using an STO-3G basis set. Their study did not use a fully optimized structure.…”

Complexes and Clusters of Water Relevant to Atmospheric Chemistry: H2O Complexes with Oxidants

“…[87] The results of Nelander's experimental study [82] are in good agreement with quantum chemical calculations. [88][89][90][91] Among the theoretical works, it is believed that the most reliable results are those of Aloisio and Francisco, [90] where calculations were carried out at the MP2/6-311 + + G(2df,2p) level of theory, and those of Aloisio et al [91] (calculations of the excitation energies of the three lowest electronic states of HOOC and H 2 O·HOOC using CASSCF and MRCI methods). It was found that the most favorable conformation of the complex is an asymmetric five-membered cyclic structure [···O(H)ÀH···OÀOÀH···] with one of the water hydrogen atoms located out of the molecular plane (Figure 12).…”

Theoretical Studies of Atmospheric Water Complexes

“…This complex H 2 0. H0 2 has been studied by Hamilton [32], but because of technology and theory limitations at that time, the calculation remained at the SCF level and the geometry was only partially optimized.…”

“…Previous work [32] on HzO· HO z performed a point-by-point partial geometry optimization and derived an almost planar structure (the HzO plane was 4°out of the HO z plane). In our studies, first we tried to determine the complex symmetry.…”

“…Previously, Hamilton [32] and Rao [33] studied the complex HzO. HO zl while Del Bene calculated the complex HzO.…”