Rate Coefficients for the Thermal Decomposition of BrONO2 and the Heat of Formation of BrONO2

Midlatitude Ozone Depletion and Air Quality Impacts from Industrial Halogen Emissions in the Great Salt Lake Basin

We report aircraft observations of extreme levels of HCl and the dihalogens Cl₂, Br₂, and BrCl in an industrial plume near the Great Salt Lake, Utah. Complete depletion of O₃ was observed concurrently with halogen enhancements as a direct result of photochemically produced halogen radicals. Observed fluxes for Cl₂, HCl, and NO_x agreed with facility-reported emissions inventories. Bromine emissions are not required to be reported in the inventory, but are estimated as 173 Mg year^-1 Br₂ and 949 Mg year^-1 BrCl, representing a major uncounted oxidant source. A zero-dimensional photochemical box model reproduced the observed O₃ depletions and demonstrated that bromine radical cycling was principally responsible for the rapid O₃ depletion. Inclusion of observed halogen emissions in both the box model and a 3D chemical model showed significant increases in oxidants and particulate matter (PM_2.5) in the populated regions of the Great Salt Lake Basin, where winter PM_2.5 is among the most severe air quality issues in the U.S. The model shows regional PM_2.5 increases of 10%-25% attributable to this single industrial halogen source, demonstrating the impact of underreported industrial bromine emissions on oxidation sources and air quality within a major urban area of the western U.S.

Delocalized π36 bond in OX2 (X=halogen) molecules

OX2 (X=halogen) molecules was studied theoretically. Calculation results show that delocalized [Formula: see text] bonds exist in their electronic structures and O atoms adopt the sp2 type of hybridization, which violates the prediction of the valence shell electron pair repulsion theory of sp3 type. Delocalization stabilization energy is proposed to measure the contribution of delocalized [Formula: see text] bond to energy decrease and proves to bring extra-stability to the molecule. These phenomena can be summarized as a kind of coordinating effect.

Temperature-Dependent Kinetics Study of the Gas-Phase Reactions of OH with n- and i-Propyl Bromide

An experimental, temperature-dependent kinetics study of the gas-phase reactions of hydroxyl radical with n-propyl bromide, OH+n-C3H7Br-->products (reaction 1), and i-propyl bromide, OH+i-C3H7Br-->products (reaction 2), has been performed over wide ranges of temperatures 297-725 and 297-715 K, respectively, and at pressures between 6.67 and 26.76 kPa by a pulsed laser photolysis/pulsed laser-induced fluorescence technique. Data sets of absolute bimolecular rate coefficients obtained in this study for reactions 1 and 2 demonstrate no correlation with pressure and exhibit positive temperature dependencies that can be represented with modified three-parameter Arrhenius expressions within their corresponding experimental temperature ranges: k1(T)=(1.32x10(-17))T1.95 exp(+25/T) cm3 molecule(-1) s(-1) for reaction 1 and k2(T)=(1.56x10(-24))T4.18exp(+922/T) cm3 molecule(-1) s(-1) for reaction 2. The present results, which extend the current kinetics data base of reactions 1 and 2 to high temperatures, are compared with those from previous works. On the basis of the present data and available data from previous studies, the following bimolecular rate coefficient temperature dependencies can be recommended for the purpose of kinetic modeling: k1(T)=(1.89x10(-19))T2.54exp(+301/T) cm3 molecule-1 s-1 for reaction 1 in a temperature range 210-725 K, and k2(T)=(2.83x10(-21))T3.1exp(+521/T) cm3 molecule(-1) s(-1) and k2(T)=(4.54x10(-24))T4.03exp(+860/T) cm3 molecule(-1) s(-1) for reaction 2 in temperature ranges 210-480 and 297-715 K, respectively.

Kinetic study of the gas-phase reaction of OH with Br2

An experimental, temperature-dependent kinetic study of the gas-phase reaction of the hydroxyl radical with molecular bromine (reaction 1) has been performed by using a pulsed laser photolysis/pulsed-laser-induced fluorescence technique over a wide temperature range of 297-766 K, and at pressures between 6.68 and 40.29 kPa of helium. The experimental rate coefficients for reaction 1 demonstrate no correlation with pressure and exhibit a negative temperature dependence with a slight negative curvature in the Arrhenius plot. A nonlinear least-squares fit with two floating parameters of the temperature-dependent k(1)(T) data set using an equation of the form k(1)(T) = AT(n) yields the recommended expression k(1)(T) = (1.85 x 10(-9))T(-0.66) cm(3) molecule(-1) s(-1) for the temperature dependence of the reaction 1 rate coefficient. The potential energy surface (PES) of reaction 1 was investigated with use of quantum chemistry methods. The reaction proceeds through formation of a weakly bound OH...Br(2) complex and a PES saddle point with an energy below that of the reactants. Temperature dependence of the reaction rate coefficient was modeled by using the RRKM method on the basis of the calculated PES.

Theoretical study of chlorine nitrates: implications for stratospheric chlorine chemistry

Reported here is a theoretical study of possible stratospheric chlorine reservoir species including isomers of chemical formula ClNO(4) and ClNO(5), in addition to the well-known ClONO(2) reservoir species. Density functional theory (DFT) in conjunction with large one-particle basis sets has been used to determine equilibrium structures, dipole moments, rotational constants, harmonic vibrational frequencies, and infrared intensities. The B3LYP functional was used since it has previously been shown to perform well for similar compounds. The equilibrium geometry and vibrational spectra of ClONO(2) are shown to be in good agreement with the experimental data and also with high-level coupled-cluster calculations reported previously. Three stable isomers have been identified for each ClNO(4) and ClNO(5). The vibrational spectrum of O(2)ClONO(2) has been compared with the available experimental data and found to be in good agreement. The relative energetics of the ClNO(4) and ClNO(5) isomers have been determined using large atomic natural orbital (ANO) basis sets in conjunction with the singles and doubles coupled-cluster method that includes a perturbational correction for triple excitations, denoted CCSD(T). Accurate heats of formation have been evaluated by computing energies for isodesmic reactions involving the ClNO(4) and ClNO(5) isomers. The stability of these molecules with respect to thermal dissociation is examined. The present study suggests that isomers of ClNO(4) and ClNO(5) may have no atmospheric chemical relevance because the atmospheric concentrations of the necessary reactants are insufficient, but it is also found that under laboratory conditions the formation of O(2)ClONO(2) cannot be ignored.