Mechanism and Kinetics of the Reaction NO3 + C2H4

A theoretical study of the gas-phase reactions of propadiene with NO3: mechanism, kinetics and insights

In this study, the conversion mechanisms and kinetics of propadiene (CH₂[double bond, length as m-dash]C[double bond, length as m-dash]CH₂) induced by NO₃ were researched using density functional theory (DFT) and transition state theory (TST) measurements. The NO₃-addition pathways to generate IM1 (CH₂ONO₂CCH₂) and IM2 (CH₂CONO₂CH₂) play a significant role. P3 (CH₂CONOCHO + H) was the dominant addition/elimination product. Moreover, the results manifested that one H atom from the -CH₂- group has to be abstracted by NO₃ radicals, leading to the final product h-P1 (CH₂CCH + HNO₃). Due to the high barrier, the H-abstraction pathway is not important for the propadiene + NO₃ reaction. In addition, the computed k_tot value of propadiene reacting with NO₃ at 298 K is 3.34 × 10^-15 cm³ per molecule per s, which is in accordance with the experimental value. The computed lifetime of propadiene oxidized by NO₃ radicals was assessed to be 130.16-6.08 days at 200-298 K and an altitude of 0-12 km. This study provides insights into the transformation of propadiene in a complex environment.

Quantum calculation on night-time degradation of 2-chloroethyl ethyl ether (CH3CH2OCH2CH2Cl) initiated by NO3 radical

A dual-level quantum chemical calculations have been carried out on the initiation of night-time degradation of 2-chloroethyl ethyl ether (CH3CH2OCH2CH2Cl) via H-abstraction by NO3 radical. Within the scope of density functional theory, the electronic structure of all the species involved in the titled reaction has been optimized at M06-2X functional along with 6-31[Formula: see text]G(d,p) basis set. A higher level of couple cluster CCSD(T) method in conjunction with 6-311[Formula: see text]G(d,p) basis set has been used for the refined energy of the species. All minima and saddle states involved in the reaction channel have been characterized on the potential energy surface (PES). From PES, it is confirmed that H-abstraction from methylene (–CH2–) of ethyl (CH3CH2–) part of CH3CH2OCH2CH2Cl follows the minimum energy path. The rate constants (individual and overall) of the titled reaction are obtained using Canonical Transition State Theory (CTST) over the temperature range of 250–350[Formula: see text]K. The atmospheric lifetime and radiative efficiency of the titled molecule have also been estimated, amounting to 0.23 years and 0.024 years, respectively. The Global Warming Potentials of the 2-chloroethyl ethyl ether in 20 years, 100 years and 500 years time horizon were found to be 0.13, 0.04 and 0.01, respectively.

Reaction Mechanism of 4-Chlorobiphenyl and the NO3 Radical: An Experimental and Theoretical Study

Experiment and theoretical chemistry calculations were conducted to elucidate the mechanism of the reaction between 4-chlorobiphenyl (4-CB) and the NO₃ radical. The degradation of PCBs was investigated mechanistically through transient absorption spectroscopy technology and high-accuracy theoretical calculation by using 4-CB as the model. Laser flash photolysis (LFP) experiments were performed at 355 nm. The main intermediate was analyzed through transient absorption spectroscopy and identified to be a charge transfer complex (CTC). The final products were identified through GC-MS analysis. The ground states and excited states of the reactants were calculated through density functional theory (DFT) method. The absorption bands at 400 and 700 nm show good agreement with the experimental results. The ratio of absorbance at 400 and 700 nm is 1.6, and the experimental value is 1.8. Analysis of the charge population indicated that one unit charge transfer from 4-CB to NO₃. The entire reaction process was divided into two phases. In the first phase, the CTC intermediate was formed by electrostatic attraction between 4-CB and the NO₃ radical. In the second phase, the most important channel of subsequent reactions is the σ-complex as an intermediate formed by N-C coupling. The final product 4-chloro,2-nitrobiphenyl was generated with the breakage of B_C-H and B_N-O, and benzene derivatives were formed by other channels.