Region-wise and state-wise synthesis of vehicular emissions in India and their mitigation due to vehicular emissions standards.

The implementation of different stages of Bharat Stage Emission standards (BSES) in India for reducing the vehicular emissions has been in different parts of the country at various points of time. A quantitative assessment of the emission standards in mitigating vehicular emissions at different Indian states will provide an estimate of achievable emissions standards for future norms. In this regard, the present work reports an assessment of the BS standards - BS-III, BS-IV and BS-VI in reducing the exhaust emissions in each of the Indian states.

Tailoring the mechanistic pathways and kinetics of OH-addition reaction of sulfoxaflor and its ecotoxicity assessment.

Sulfoxaflor is one of the widely used insecticides in agricultural lands to protect crops from insects. Due to its persistent nature, sulfoxaflor is identified as an environmental pollutant. In the present work, the mechanism and kinetics of sulfoxaflor degradation initiated by OH radical addition reaction are studied by using quantum chemical calculations.

Chemical dynamics simulations of energy transfer in CH and N collisions.

Chemical dynamics simulations have been performed to study the energy transfer from a hot N bath at 1000 K to CH fuel at 300 K at different bath densities ranging from 1000 kg m to 30 kg m. At higher bath densities, the energy transfer from the bath to the fuel was rapid and as the density was decreased, the energy transfer rate constant decreased. The results show that in combustion systems with CH as a prototype fuel, the super pressure regimes control the fuel heating and combustion processes.

Autoxidation of Formaldehyde with Oxygen-A Comparison of Reaction Channels.

The autoxidation of formaldehyde through initiation by triplet oxygen is studied via two initial steps: (1) H-atom abstraction and (2) O addition reaction. The reaction energy profiles show that the reactions are thermodynamically and kinetically demanding. A comparison of the pathways of these initial reactions and the search for a less energy-demanding pathway is presented.

Mechanism and kinetics for the reaction of methyl peroxy radical with O.

Quantum chemical calculations and dynamics simulations were performed to study the reaction between methyl peroxy radical (CHO) and O. The reaction proceeds through three different pathways (1) H-atom abstraction, (2) O addition and (3) concerted H-atom shift and O addition reactions. The concerted H-atom shift and O addition pathway is the most favourable reaction both kinetically and thermodynamically.

Direct Dynamics Simulations of the CH + O Reaction at High Temperature.

Direct dynamics simulations with the M06/6-311++G(d,p) level of theory were performed to study the CH + O reaction at 1000 K temperature on the ground state singlet surface. The reaction is complex with formation of many different product channels in highly exothermic reactions. CO, CO, HO, OH, H, O, H, and HCO are the products formed from the reaction.

Direct Dynamics Simulations of the Unimolecular Decomposition of the Randomly Excited CHO Criegee Intermediate. Comparison with CH + O Reaction Dynamics.

The CH + O reaction has a quite complex ground state singlet potential energy surface (PES). There are multiple minima and transition states before forming the 10 possible reaction products. A previous direct chemical dynamics simulation at the UM06/6-311++G(d,p) level of theory ( 2019, 123, 4360-4369) found that reaction on this PES is predominantly direct without trapping in the potential minima.

Mechanism and kinetics of diuron oxidation by hydroxyl radical addition reaction.

Diuron is a phenyl urea herbicide used to control weeds in agricultural lands. The degradation of diuron in the atmosphere takes place dominantly via reaction with OH radicals. In this work, the OH addition reaction of diuron has been studied by using density functional theory methods M06-2X, ωB97X-D and MPWB1K with 6-31G(d,p) basis set.

Molecule-Induced Radical Formation (MIRF) Reactions-A Reappraisal.

Radical chain reactions are commonly initiated through the thermal or photochemical activation of purpose-built initiators, through photochemical activation of substrates, or through well-designed redox processes. Where radicals come from in the absence of these initiation strategies is much less obvious and are often assumed to derive from unknown impurities. In this situation, molecule-induced radical formation (MIRF) reactions should be considered as well-defined alternative initiation modes.

Potential Energy Curves for Formation of the CHO Criegee Intermediate on the CH + O Singlet and Triplet Potential Energy Surfaces.

The potential energy curves (PECs) for the interaction of CH with O in singlet and triplet potential energy surfaces (PESs) leading to singlet and triplet Criegee intermediates (CHOO) are studied using electronic structure calculations. The bonding mechanism is interpreted by analyzing the ground state multireference configuration interaction (MRCI) wave function of the reacting species and at all points along the PES. The interaction of CH with O on the singlet surface leads to a flat long-range attractive PEC lacking any maxima or minima along the curve.

Radical-Pair Formation in Hydrocarbon (Aut)Oxidation.

The reaction profiles for the uni- and bimolecular decomposition of benzyl hydroperoxide have been studied in the context of initiation reactions for the (aut)oxidation of hydrocarbons. The unimolecular dissociation of benzyl hydroperoxide was found to proceed through the formation of a hydrogen-bonded radical-pair minimum located +181 kJ mol above the hydroperoxide substrate and around 15 kJ mol below the separated radical products. The reaction of toluene with benzyl hydroperoxide proceeds such that O-O bond homolysis is coupled with a C-H bond abstraction event in a single kinetic step.

Direct Dynamics Simulations of the CH + O Reaction on the Ground- and Excited-State Singlet Surfaces.

In a previous work [ Lakshmanan , S. ; J. Phys.

Mechanism and kinetics of the oxidation of dimethyl carbonate by hydroxyl radical in the atmosphere.

The mechanism and kinetics for the reaction of dimethyl carbonate (DMC) with OH radical have been studied by using quantum chemical methods. Four reaction pathways were identified for the initial reaction. In the first two pathways, hydrogen atom abstraction is taking place and alkyl radical intermediate is formed with the energy barrier of 6.

Direct Dynamics Simulation of the Thermal CH + O Reaction. Rate Constant and Product Branching Ratios.

The reaction of CH with O is of fundamental importance in combustion, and the reaction is complex as a result of multiple extremely exothermic product channels. In the present study, direct dynamics simulations were performed to study the reaction on both the singlet and triplet potential energy surfaces (PESs). The simulations were performed at the UM06/6-311++G(d,p) level of theory.

OO bond homolysis in hydrogen peroxide.

OO bond homolysis in hydrogen peroxide (H O ) has been studied using theoretical methods of four conceptually different types: hybrid DFT (B3LYP, M06-2X), double-hybrid DFT (B2-PLYP), coupled-cluster (CCSD(T)), and multiconfigurational (CASPT2). In addition, the effects of basis set size have also been analyzed. For all of these methods, the OO bond homolysis in hydrogen peroxide has been found to proceed through hydrogen bonded radical pair complexes.

Initiation Chemistries in Hydrocarbon (Aut)Oxidation.

For the (aut)oxidation of toluene to benzyl hydroperoxide, benzyl alcohol, benzaldehyde, and benzoic acid, the thermochemical profiles for various radical-generating reactions have been compared. A key intermediate in all of these reactions is benzyl hydroperoxide, the heat of formation of which has been estimated by using results from CBS-QB3, G4, and G3B3 calculations. Homolytic O-O bond cleavage in this hydroperoxide is strongly endothermic and thus unlikely to contribute significantly to initiation processes.