Photochemical Water Decomposition in the Troposphere: DFT Study with a Symmetrized Kohn–Sham Formalism

Abstract

Photochemical reaction of the electronically excited NO(2)* species with the water molecule is studied in terms of a new version of density functional theory by selecting the specific (2)A'' symmetry of the whole system, which is different from the ground-state pattern. The excited C(2)A(2) state of the NO(2) molecule is found to be distorted to the equilibrium structure O=N-O(.), which poses the (2)A'' symmetry in the C(s) point group. With the B3LYP functional it is shown that such an electronically excited NO(2)* molecule, generated by visible light (λ=420 nm), can react with water vapor to produce OH+HONO species, an important source of tropospheric hydroxyl radicals. This photochemical process can be considered as a possible mechanism of atmosphere self-cleaning.

Vibronic structures and dynamics of the predissociating dimethyl sulfide and its isotopomers (CH3SCH3, CD3SCD3, CH3SCD3) at the conical intersection

“…The contribution of the singlet-to-triplet excitation cannot be completely excluded. 35,36 The Lorentzian fits to the individual vibronic bands give the full widths at half-maxima of B100 cm À1 corresponding to the lifetime of B100 fs from the uncertainty principle. The band width remains more or less constant for all vibronic bands.…”

Theoretical study of the triplet state aryl cations recombination: A possible route to unusually stable doubly charged biphenyl cations

“…According to this concept, the nature of the activation barrier in bimolecular chemical reactions being determined by exchange repulsion between two closed shell molecules can also be interpreted in terms of their excited triplet state behavior, as shown in Figure . The height of the barrier and the heat of reaction are determined predominantly by the properties of the “double–triplet” singlet excited states of the reactants …”

“…The role of the double–triplet singlet state becomes more natural and more important in those reactions when it can be realized in a form of the ground state reactivity. This happens in the recombination of two triplet reactants: CH 2 ( 3 B 1 ) + CH 2 ( 3 B 1 ) = C 2 H 4 ( 1 A g ), an example representing the calculated reaction 2NO + O 2 ( 3 Σ g − ) = 2NO 2 . Here, the two NO radicals and molecular oxygen collide within the zero spin state, which finally dissociates to two NO 2 molecules.…”

Theoretical Investigation of the Photoexcited NO2+H2O reaction at the Air–Water Interface and Its Atmospheric Implications

“…The reaction mechanism of Equation (5 b) was theoretically studied by Minaev et al., who described the process as hydrogen transfer from water to distorted NO 2 in the third 2 A′′ electronic state, after formation of an intermediate complex that prevents vibronic relaxation to the ground state. The process is exoergic and has an activation barrier of 21.1 kJ mol −1 .…”

“…The authors confirm the possibility for excited NO 2 * to react with water but they report small OH yields [10] k 5b /k 5 = 6 10 À6 -1.4 10 À4 ,f rom which one deduces k 5b % 10 À15 -3.4 10 À14 cm 3 molecule À1 ·s À1 ,t hat is one to two orders of magnitude smaller than the value of Li et al [7] (we assume k 5 % k 5a % 1.7 10 À10 cm 3 molecule À1 s À1 ). [6] The reaction mechanism of Equation (5 b) was theoretically studied by Minaev et al, [11] who described the process as hydrogen transfer from water to distorted NO 2 in the third 2 A'' electronic state, after formation of an intermediate complex that prevents vibronic relaxation to the ground state. The process is exoergic and has an activation barriero f2 1.1 kJ mol À1 .…”