Mechanism and rate constants for ammonia photochemical oxidation with O2 on the singlet and triplet potential energy surfaces

The mechanism and thermodynamic of NH₃ + O₂ reaction on the singlet and triplet potential energy surfaces (PES), were carried out using the RMP2 and CCSD (T)//RMP2 theoretical approaches in connection with the 6-311++G(d, p) basis set. Three pre-reactive complexes, ¹C1, ¹C2, and ³C1 on the singlet and triplet PES were formed between ammonia and molecular oxygen. With variety of pre-reactive complexes, six types of products are obtained, of which two types are found to be thermodynamically stable. The mechanistic properties of all products channels are discussed. Results show that production of HONO + H₂ and HN(OH)₂ are the main reaction channels in thermodynamic viewpoint with the Gibbs free energy of ?G° = ?34.681 and ?27.153 kcal/mol, respectively. Rate constants of the title reaction over the temperature range of (200–1000 K) show kinetic products are different from thermodynamic products.     

Theoretical study on the atmospheric formation of sulfur trioxide as the primary agent for acid rain

The reaction mechanism of SO₂ with O₃ on the singlet potential energy surface has been investigated theoretically at the G3MP2B3//B3LYP/6-311+G(3df) level of theory. The reactants are initially associated with adducts IN1(O₂S–OOO) and IN2(OS-cyclic O₄) in a barrier-less process. Subsequently, these adducts undergo isomerization and dissociation processes to produce cis-OSOO + ³O₂, SO₃(C _s ) + ³O₂ and SO₃(D _3h ) + ³O₂ products. The SO₃(D _3h ) + ³O₂ is major product and the cis-OSOO + ³O₂ and SO₃(C _s ) + ³O₂ are minor products. No stable pathway has been found for the formation of trans-OSOO and cyclic-SOOO isomers in the reaction of SO₂ + O₃. For major product, the rate constant of SO₂ + O₃ reaction is 2.30 × 10⁻²³ cm³ molecule⁻¹ s⁻¹, at room temperature and atmospheric pressure.     

Mechanistic Study on the Ozone‐Mercury Reaction and the Effect of Water and Water Dimer Molecules

The thermodynamics and mechanism of the reaction of elemental mercury with ozone has been studied computationally. The effect of water and water dimer molecules on the reaction has also been investigated. For dry reaction, we obtained two pathways and geometry optimization, atoms in molecules analysis and vibrational frequencies of all component of reaction have been used for confirming of reaction mechanism. Thermodynamic variable of reaction has been calculated. For the reaction in the presence of the water, our studies focus on ozone‐mercury complex reaction with water and water dimer and obtained the mechanism of reactions. Comparison of wet and dry reaction shows the energy profile of reaction decreases with water molecule correspond to experimental prediction. Calculated thermodynamic variable of all reaction shows the Gibbs free energy of reaction decreases with the number of water molecule.     

Theoretical study of reaction mechanism for Se + O<Subscript>3</Subscript>

The reaction mechanism of Se + O₃ on the singlet potential energy has been investigated at CCSD(T)/6-311++G(2df,2pd) level of theory based on the geometric parameters optimized at the B3LYP/6-311++G(3df,3pd) level of theory. The calculated results show that the reactants are firstly associated into the adduct Se–O₃ with any intrinsic barrier. Subsequently, through a variety of transformations of isomer Se–O₃, two kinds of products P₁(SeO₃(D_3h)) and P₂(SeO + ³O₂) are obtained. The breakage and formation of the chemical bonds in the reaction have been studied by the topological analysis of electronic density. The topological analysis results show that the ring transitional structure region does not only occur in cis-OSeOO → SeO₃(C_s) process but also occur in SeO₃(C_s) → SeO₃(D_3h).     

Concentration dependent tautomerism in green [Cu(HL¹)(L²)] and brown [Cu(L¹)(HL²)] with H₂L¹ = (E)-N'-(2-hydroxy-3-methoxybenzylidene)benzoylhydrazone and HL² = pyridine-4-carboxylic (isonicotinic) acid

The in situ formed hydrazone Schiff base ligand (E)-N'-(2-hydroxy-3-methoxybenzylidene)benzoylhydrazone (H?L1) reacts with copper(II) acetate in ethanol in the presence of pyridine-4-carboxylic acid (isonicotinic acid, HL2) to green-[Cu(HL1)(L2)]·H?O·C?H?OH (1) and brown-[Cu(L1)(HL2)] (2) complexes which crystallize as concomitant tautomers where either the mono-anion (HL1)? or di-anion (L1)2? of the Schiff base and simultaneously the pyridine-carboxylate (L2)? or the acid (HL2) (both through the pyridine nitrogen atom) function as ligands. The square-planar molecular copper(II) complexes differ in only a localized proton position either on the amide nitrogen of the hydrazone Schiff base in 1 or on the carboxyl group of the isonicotin ligand in 2. The proportion of the tautomeric forms in the crystalline solid-state can be controlled over a wide range from 1:2 = 95?:?5 to ～2?:?98 by increasing the solution concentration. UV/Vis spectral studies show both tautomers to be kinetically stable (inert), that is, with no apparent tautomerization, in acetonitrile solution. The UB3LYP/6-31+G* level optimized structures of the two complexes are in close agreement with experimental findings. The solid-state structures feature 1D hydrogen-bonded chain from charge-assisted O((-))H-N and O-H((-))N hydrogen bonding in 1 and 2, respectively. In 1 pyridine-4-carboxylate also assumes a metal-bridging action by coordinating a weakly bound carboxylate group as a fifth ligand to a Cu axial site. Neighboring chains in 1 and 2 are connected by strong π-stacking interactions involving also the five- and six-membered, presumably metalloaromatic Cu-chelate rings.     

Mechanistic study on the atmospheric formation of acid rain base on the sulfur dioxide

The reaction pathways of acid rain formation from reaction of sulfur dioxide vapor and water vapor on the singlet potential energy surface have been investigated theoretically. The calculated results show that the reactants are initially associated with the adduct SO₂–H₂O through a barrier less process. Subsequently, via a variety of transformations of isomer SO₂–H₂O, three kinds of products H₂SO₃, SO₃ + H₂, and H₂O₂ + ³SO are obtained. The cleavage and formation of the chemical bonds in the reaction pathways have been discussed using the structural parameters. Also, by means of the transition states and their connected intermediates or products at the CCSD(T)//B3LYP level, mechanism of H₂O + SO₂ reaction on the singlet potential energy surface are plotted. The calculation results show that the most suitable reaction pathways are the formation of H₂SO₃. Finally, the rate constants have been calculated only for these suitable pathways by the RRKM and TST theories at temperature range of 250–2500 K.     

Computational mechanistic study of methanol and molecular oxygen reaction on the triplet and singlet potential energy surfaces

The reaction of CH₃OH with the O₂ on the triplet and singlet potential energy surfaces (PES) was carried out using the B3LYP, MP2, and CCSD(T)//B3LYP theoretical approaches in connection with the 6-311++G(3df–3pd) basis set. Three pre-reactive complexes, ¹C1, ¹C2, and ³C1, on the singlet and triplet PES were formed between methanol and molecular oxygen. From a variety of the complexes, seven types of products are obtained, of which four types are found to be thermodynamically stable. Results reveal that there exists one intersystem crossing between triplet and singlet PES. For P4 adduct that is the main and kinetically the most favorable product, the rate constants are calculated in the temperature range of 200–1,000 K in the reliable pathway.     

Investigation of the formation of acid rain based on the sulfur tetroxide (SO4 (C2v)) and OH radical reaction

Structural Chemistry - The reaction pathways of sulfur tetroxide (SO4 (C2v)) with OH radical have been investigated at the MP2/6-31++G(d,p) and G3MP2B3 levels. The mechanism I (Transfer of O-atom...     

Atmospheric reaction pathways of methanimine and nitroxyl: a theoretical study

Structural Chemistry - The kinetics and mechanisms of atmospheric reaction of methanimine (H2CNH) with nitroxyl on the singlet surface were studied by employing DFT, MP2, and CCSD(T) methods along...     

Vanadiumoxo–aroylhydrazone complexes: Synthesis,structure and DFT calculations

The aroylhydrazone Schiff base ligands (E)-N’-(2-hydroxybenzylidene)benzohydrazide = H₂L¹, (E)-N’-(2-hydroxy-3-methoxybenzylidene)benzohydrazide = H₂L² and = (E)-N’-(5-bromo-2-hydroxybenzylidene)benzohydrazide = H₂L³ gave the vanadium(V)oxo-aroylhydrazone complexes [V^VOL¹(OCH₃)(OHCH₃] (1), [V^VOL²(OCH₃)(OHCH₃]·CH₃OH (2) and [V^VOL³(OCH₃)(OHCH₃] (3) on reaction with vanadium(IV) oxide acetylacetonate. The complexes were characterized by spectroscopic methods in the solid state (IR) and in solution (UV–Vis, ¹H NMR). Single crystal X-ray analysis was performed with 3. In methanol solution six-coordinated V^VOL³(OCH₃)(OHCH₃) was formed. V^IV was oxidized to V^v by aerial oxygen in the synthesis. In the VO₅N coordination sphere the alcohol oxygen lies trans to the oxo oxygen. The general V–O bond length order is oxo < methoxylato < phenoxidic < enolato < alcoholic. The complexes are mononuclear, but intermolecular O–H?N hydrogen bonding affords a zigzag chain. DFT calculations on complex 3 reproduced the geometric parameters, IR and UV–Vis spectroscopic data well in a reasonable range.