Thermochemistry and kinetics of the Cl + O2 association reaction

Theoretical Study of ClOO + NO Reaction: Mechanism and Kinetics

Theoretical investigations are performed on mechanism and kinetics of the reaction of halogen peroxy radical ClOO with NO radical. The electronic structure information for both of the singlet and triplet potential energy surfaces (PESs) is obtained at the MP2/6-311 + G(2df) level of theory, and the single-point energies are refined by the CCSD(T)/6-311 + G(2df) level. The rate constants for various product channels of the reaction in the pressure range of 1-7600 Torr are predicted. The main results are as follows: On the singlet surface, the addition-elimination mechanism is the most important. First, the N atom of the NO radical can attack the O atom of the ClOO radical to form an energy-riched intermediate IM1 ClOONOtp (21.3 kcal/mol) barrierlessly, then IM1 could isomerizes to IM2 ClOONOcp (22.1 kcal/mol) via a low energy barrier. Both IM1 and IM2 can dissociate to the primary product P₁ ClNO + ¹O₂ and the secondary product P₂ ClO + NO₂. On the triplet surface, the direct Cl-abstraction reaction is the most feasible pathway. The Cl-abstraction can take place via a van der Waals complex, ³IM1 ONClOO (4.1 kcal/mol), then it fragments readily to give P₁' ClNO + ³O₂ with a small barrier. The kinetic calculations show that at low temperatures, the singlet bimolecular product P₁ is the primary product, while at high temperatures, the triplet product P₁' becomes the primary one; only at high pressures and low temperatures, the unimolecular products IM1 and IM2 can be found with quite small yields. At experimentally measured temperature 213 K, ClNO is the primary product in the whole pressure range, which is consistent with the previous experiment. The present study may be useful for further experimental studies for the title reaction.

Kinetic Study of the ClOO + NO Reaction Using Cavity Ring-Down Spectroscopy

Cavity ring-down spectroscopy was used to study the reaction of ClOO with NO in 50-150 Torr total pressure of O2/N2 diluent at 205-243 K. A value of k(ClOO+NO) = (4.5 +/- 0.9) x 10(-11) cm3 molecule(-1) s(-1) at 213 K was determined (quoted uncertainties are two standard deviations). The yield of NO(2) in the ClOO + NO reaction was 0.18 +/- 0.02 at 213 K and 0.15 +/- 0.02 at 223 K. An upper limit of k(ClOO+Cl2) < 3.5 x 10(-14) cm3 molecule(-1) s(-1) was established at 213 K. Results are discussed with respect to the atmospheric chemistry of ClOO and other peroxy radicals.

Formation and Characterization of the XeOO+ Cation in Solid Argon

This report presents the preparation and characterization of a xenon-containing cationic radical species, XeOO+. The XeOO+ cation was produced either by co-deposition of the reactive species generated by laser ablation of different transition metals with dioxygen and xenon mixtures in excess argon or by condensation of high-frequency discharged O2/Xe/Ar mixtures at 12 K and is identified by infrared absorptions. High-level quantum chemical calculations indicate that XeOO+ has a bent structure with direct xenon-oxygen dative bonding, and the doublet ground state is much more stable than the Xe + O2+ reactants.

Kinetics and product studies of the reaction of Br, Cl, and NO with ClOOCl using discharge-flow mass spectrometry

The kinetics of the reactions Cl + ClOOCl --> products, Br + ClOOCl --> products (7), and NO + ClOOCl --> products have been studied as a function of temperature at 1 Torr total pressure using a discharge-flow mass spectrometric technique. The measured rate coefficients, expressed in Arrhenius form, are k5 = (7.60 +/- 0.56) x 10(-11)exp((65.4 +/- 17.9)/T) cm3 s(-1) for 217 K < T < 298 K, and k7 = (5.88 +/- 0.50) x 10(-12) exp(-173 +/- 20/T) cm3 s(-1) for 223 K < T< 298 K. The observed temperature dependencies of these rate coefficients indicate a common direct halogen atom abstraction mechanism. Mass spectral product studies indicate that BrCl is the only major Br-containing product from reaction. Extensive product studies were used to estimate that the peroxide form of the ClO-dimer is formed in > 90% yield from the ClO self-reaction. No evidence for the formation of ClOClO and ClClO2 was observed. No reaction between NO and ClOOCl was observed and an upper limit of k8 < 1 x 10(-15) cm3 s(-1) for 220 K < T < 298 K was determined.

Fourier transform microwave spectroscopy and Fourier transform microwave–millimeter wave double resonance spectroscopy of the ClOO radical

Pure rotational spectra of the ClOO radical for the (35)Cl and (37)Cl isotopomers have been observed using Fourier transform microwave and Fourier transform microwave-millimeter wave double resonance spectroscopy. The rotational, centrifugal, spin-rotation coupling, and hyperfine coupling constants have been determined by least-squares fits of the observed transition frequencies. The molecular constants indicate that the electronic ground state is 2A". The r(0) structure is determined to be r(0)(ClO)=2.075 A, r(0)(OO)=1.227 A, and theta;(0)(ClOO)=116.4 degrees . Several highly accurate ab initio calculations have also been performed. Some of them turned out to be inaccurate because it is necessary to take into account both static and dynamic electronic correlations. Only multireference (single and double) configuration interaction calculations with large basis sets reproduce the present experimental results. The anharmonic force constants obtained by the ab initio calculations are used to determine the r(e) structure, r(e)(ClO)=2.084(1) A, r(e)(OO)=1.206(2) A, and theta;(e)(ClOO)=115.4(1) degrees . Unique features of the ClOO radical have become clear by the present experiment and the ab initio calculations.