Kinetic study of gas-phase Lu(D3/2) with O2, N2O and CO2

The second-order rate constants of gas-phase Lu(²D_3/2) with O₂, N₂O and CO₂ from 348 to 573 K are reported. In all cases, the reactions are relatively fast with small barriers. The disappearance rates are independent of total pressure indicating bimolecular abstraction processes. The bimolecular rate constants (in molecule⁻¹ cm³ s⁻¹) are described in Arrhenius form by k(O₂)=(2.3±0.4)×10⁻¹⁰exp(−3.1±0.7 kJmol⁻¹/RT), k(N₂O)=(2.2±0.4)×10⁻¹⁰exp(−7.1±0.8 kJmol⁻¹/RT), k(CO₂)=(2.0±0.6)×10⁻¹⁰exp(−7.6±1.3 kJmol⁻¹/RT), where the uncertainties are ±2σ.     

Temperature dependence of the reaction C2H (C2D) + O2 between 295 and 700 K

The rate coefficients for the reactions of C₂H and C₂D with O₂ have been measured in the temperature range 295 K T 700 K. Both reactions show a slightly negative temperature dependence in this temperature range, with k_C2H+O2 = (3.15 ± 0.04) × 10⁻¹¹ (T/295 K)^{−(0.16 ± 0.02)} cm³ molecule⁻¹ s⁻¹. The kinetic isotope effect is k_C2H/k_C2D = 1.04 ± 0.03 and is constant with temperature to within experimental error. The temperature dependence and the C₂H + O₂ kinetic isotope effect are consistent with a capture-limited metathesis reaction, and suggest that formation of the initial HCCOO adduct is rate-limiting.     

Direct kinetic studies of the reactions of 2-butoxy radicals with NO and O2

This Letter reports the first kinetic study of 2-butoxy radicals to employ direct monitoring of the radical. The reactions of 2-butoxy with O₂ and NO are investigated using laser-induced fluorescence (LIF). The Arrhenius expressions for the reactions of 2-butoxy with NO (k₁) and O₂ (k₂) in the temperature range 223–311 K have been determined to be k₁=(7.50±1.69)×10⁻¹²×exp((2.98±0.47) kJmol⁻¹/RT) cm³ molecule⁻¹ s⁻¹ and k₂=(1.33±0.43)×10⁻¹⁵×exp((5.48±0.69) kJmol⁻¹/RT) cm³ molecule⁻¹ s⁻¹. No pressure dependence was found for the rate constants of the reaction of 2-butoxy with NO at 223 K between 50 and 175 Torr.     

The multichannel reaction NH2 + NH2 at ambient temperature and low pressures

NH₂ profiles were measured in a discharge flow reactor at ambient temperature by monitoring reactants and products with an electron impact mass spectrometer. At the low pressures used (0.7 and 1.0 mbar) the gas-phase self-reaction is dominated by a ‘bimolecular’ H₂-eliminating exit channel with a rate coefficient of k_3b(300 K) = (1.3 ± 0.5) × 10⁻¹² cm³ molecule⁻¹ s⁻¹ and leading to N₂H₂ + H₂ or NNH₂ + H₂. Although the wall loss for NH₂ radicals is relatively small (k_w ≈ 6–14 s⁻¹), the contribution to the overall NH₂ decay is important due to the relatively slow gas-phase reaction. The heterogeneous reaction yields N₂H₄ molecules.     

Rates of the reactions CN + H2CO and NCO + H2CO in the temperature range 294–769 K

The rate coefficients of the reactions: (1) CN + H₂CO → products and (2) NCO + H₂CO → products in the temperature range 294–769 K have been determined by means of the laser photolysis-laser induced fluorescence technique. Our measurements show that reaction (1) is rapid: k₁(294 K) = (1.64 ± 0.25) x 10⁻¹¹ cm³ molecule⁻¹ s⁻¹; the Arrhenius relation was determined as k₁ = (6.7 ± 1.0) x 10⁻¹¹ exp[(−412 ± 20)/T] cm³ molecule⁻¹ s⁻¹. Reaction (2) is approximately a tenth as rapid as reaction (1) and the temperature dependence of k₂ does not conform to the Arrhenius form: k₂ = 4.62 x 10⁻¹⁷T^1.71 exp(198/T) cm³ molecule⁻¹ s⁻¹. Our values are in reasonable agreement with the only reported measurement of k₁; the rate coefficients for reaction (2) have not been previously reported.     

Experimental and theoretical investigation of the reaction CF3 + NO + M → CF3NO + M from 0.5 to 12 Torr and from 253 to 373 K

The kinetics of the association reaction of CF₃ with NO was studied as a function of temperature near the low-pressure limit, using pulsed laser photolysis and time-resolved mass spectrometry. CF₃ radicals were generated by photolysis of CF₃I at 248 nm and the kinetics was determined by monitoring the time-resolved formation of CF₃NO. The bimolecular rate constants were measured from 0.5 to 12 Torr, using nitrogen as the buffer gas. The results are in very good agreement with recent data published by Vakhtin and Petrov, obtained at room temperature in a higher pressure range and, therefore, the two studies are quite complementary. A RRKM model was developed for fitting all the data, including those of Vakhtin and Petrov and for extrapolating the experimental results to the low- and high-pressure limits. The rate expressions obtained are the following: k₁(0) = (3.2 ± 0.8) × 10⁻²⁹ (T/298)^{−(3.4±0.6)} cm⁶ molecule⁻² s⁻¹ for nitrogen used as the bath gas and k₁(∞) = (2.0 ± 0.4) × 10⁻¹¹ (T/298)^(0±1) cm³ molecule⁻¹ s⁻¹. RRKM calculations also help to understand the differences in reactivity between CF₃ and other radicals, for the same association reaction with NO.     

Kinetics study of the gas-phase reactions of C2F5OC(O)H and n-C3F7OC(O)H with OH radicals at 253–328 K

The rate constants, k₁ and k₂ for the reactions of C₂F₅OC(O)H and n-C₃F₇OC(O)H with OH radicals were measured using an FT-IR technique at 253–328 K. k₁ and k₂ were determined as (9.24 ± 1.33) × 10⁻¹³ exp[−(1230 ± 40)/T] and (1.41 ± 0.26) × 10⁻¹² exp[−(1260 ± 50)/T] cm³ molecule⁻¹ s⁻¹. The random errors reported are ±2 σ, and potential systematic errors of 10% could add to the k₁ and k₂. The atmospheric lifetimes of C₂F₅OC(O)H and n-C₃F₇OC(O)H with respect to reaction with OH radicals were estimated at 3.6 and 2.6 years, respectively.     

Collisional quenching of electronically excited germanium atoms, Ge[4p(S0)], by small molecules investigated by time-resolved atomic resonance absorption spectroscopy

The collisional quenching of electronically excited germanium atoms, Ge[4p²(¹S₀)], 2.029 eV above the 4p²(³P₀) ground state, has been investigated by time-resolved atomic resonance absorption spectroscopy in the ultraviolet at λ = 274.04 nm [4d(¹P₁⁰) ← 4p²(¹S₀)]. In contrast to previous investigations using the ‘single-shot mode’ at high energy, Ge(¹S₀) has been generated by the repetitive pulsed irradiation of Ge(CH₃)₄ in the presence of excess helium gas and added gases in a slow flow system, kinetically equivalent to a static system. This technique was originally developed for the study of Ge[4p²(¹D₂)] which had eluded direct quantitative kinetic study until recently. Absolute second-order rate constants obtained using signal averaging techniques from data capture of total digitised atomic decay profiles are reported for the removal of Ge(¹S₀) with the following gases (k_R in cm³ molecule⁻¹ s⁻¹, 300 K): Xe, 7.1 ± 0.4 × 10⁻¹³; N₂, 4.7 ± 0.6 × 10⁻¹²; O₂, 3.6 ± 0.9 × 10⁻¹¹; NO, 1.5 ± 0.3 × 10⁻¹¹; CO, 3.4 ± 0.5 × 10⁻¹²; N₂O, 4.5 ± 0.5 × 10⁻¹²; CO₂, 1.1 ± 0.3 × 10⁻¹¹; CH₄, 1.7 ± 0.2 × 10⁻¹¹; CF₄, 4.8 ± 0.3 × 10⁻¹²; SF₆, 9.5 ± 1.0 × 10⁻¹³; C₂H₄, 3.3 ± 0.1 × 10⁻¹⁰; C₂H₂, 2.9 ± 0.2 × 10⁻¹⁰; Ge(CH₃)₄, 5.4 ± 0.2 × 10⁻¹¹. The results are compared with previous data for Ge(¹S₀) derived in the single-shot mode where there is general agreement though with some exceptions which are discussed. The present data are also compared with analogous quenching rate data for the collisional removal of the lower lying Ge[4p²(¹D₂)] state (0.883 eV), also characterized by signal averaging methods similar to that described here.     

Flash photolysis/temperature jump study of the vibrational relaxation of N2O(010) by O(P) and NO

This survey begins with the photochemistry at 254 nm and 298 K in the system H₂O₂COO₂RH, the primary objective of which is to determine the rate constants for the reaction OH + RH → H₂O + R relative to the well-known rate constant for the reaction OH + CO → CO₂ + H. Inherent in the scheme is that the reaction HO₂+CO→OH+CO₂ is negligible compared with the OH reaction, and a literature consensus gives k_HO2 < 10⁻¹⁹ cm³ molecule⁻¹ s⁻¹, or some 10⁶ less than k_OH at 298 K. Theoretical calculations establish that the first stage in the HO₂ reaction is the formation of a free radical intermediate HO₂ + CO → HOOCO (perhydroxooxomethyl) which decomposes to yield the products, and that the rate of formation of the intermediate is equal to the rate of formation of the products. The structure of the intermediate and a reaction profile are shown.

High temperature rate data reported subsequent to the data in the consensus and theoretical calculations lead here to a recommendation that, in the range 250–800 K, k_HO2 = 3.45 × 10⁻¹²T^1/2 exp(1.15 × 10⁴/T) cm³ molecule⁻¹ s⁻¹, the hard-sphere-collision Arrhenius modification. This yields k_HO2(298) = 1.0 × 10⁻²⁷ cm³ molecule⁻¹ s⁻¹ or some 10¹⁴ slower than k_OH(298).     

State-selected reaction and relaxation of CH with H2

The state-selected reaction of CH(X₂Πν″ = 0, 1) with H₂ has been studied, in which CH was generated by IRMPD of a precursor gas, CH₃OH. The subsequent evolution of CH (ν″ = 0, 1) was monitored by the sensitive LIF technique. For the ground state and vibrationally excited state CH, the reaction with H₂ is found to depend on the total pressure in the sample cell at room temperature, which suggests that the reaction proceeds through an intermediate adduct, CH₃. The backward dissociation process is found to depend on the buffer pressure, which can be rationalized via a collision-induced backward dissociation. The decay rates of CH (ν″ = 0, 1) due to collisions with H₂ and Ar at a buffer pressure of 10 Torr are k_H2 (ν″ = 1) = (2.3±0.1) × 10⁻¹ cm³ molecule⁻¹ s⁻¹ and k_Ar (ν″ = 1) = (4.4±0.1) × 10⁻¹³ cm³ molecule⁻¹ s⁻¹. Possible effects of the vibrational excitation on the reaction rate of CH (ν″ = 1) are discussed.     

Rate constants for the reaction of OH radicals with CH3CN, C2H5CN AND CH2=CH-CN in the temperature range 298–424 K

Rate constants for the reactions of OH with CH₃CN, CH₃CH₂CN and CH₂=CH-CN have been measured to be 5.86 × 10⁻¹³ exp(−1500 ± 250 cal mole⁻¹/RT), 2.69 × 10⁻¹³ exp(−1590 ± 350 cal mole⁻¹/RT and 4.04 × 10⁻¹² cm³ molecule⁻¹ s⁻¹, respectively in the temperature range 298–424 K. These results are discussed in terms of the atmospheric lifetimes of nitrfles.     

Pulse radiolysis study of reactions of alkyl and alkylperoxy radicals originating from methyl tert-butyl ether in the gas phase

UV spectra and kinetics for the reactions of alkyl and alkylperoxy radicals from methyl tert-butyl ether (MTBE) were studied in 1 atm of SF₆ by the pulse radiolysis-UV absorption technique. UV spectra for the radical mixtures were quantified from 215 to 340 nm. At 240 nm. σ_R = (2.6 ± 0.4) × 10⁻¹⁸ cm² molecule⁻¹ and σ_RO2 = (4.1 ± 0.6) × 10⁻¹⁸ cm² molecule⁻¹ (base e). The rate constant for the self-reaction of the alkyl radicals is (2.5 ± 1.1) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹. The rate constants for reaction of the alkyl radicals with molecular oxygen and the alkylperoxy radicals with NO and NO₂ are (9.1 ± 1.5) × 10⁻¹³, (4.3 ± 1.6) × 10⁻¹² and (1.2 ± 0.3) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹, respectively. The rate constants given above refer to reaction at the tert-butyl side of the molecule.     

Cooperative two-photon-induced chemical bond formation during a Kr+F2 collision to form KrF

The reactive Kr⁺F₂⁻ potential energy surface is probed by two-photon, laser-induced chemical bond formation during a Kr+F₂ collision. This is compared with the pulsed laser excitation (two-photon) of Kr(2p₉) followed by collision with F₂ leading to the formation of KrF(B, C). In addition to reporting the excitation spectrum for the two-phonon-induced collision process, these techniques were used to determine quenching rate constants of Kr₂F^*. Quenching by Xe gives XeF(B, C) with rate constant (1.5±0.2)×10⁻¹⁰ cm³ s⁻¹; the quenching rate constant for F₂ is (1.5±0.2)×10⁻¹⁰ cm³ s⁻¹, and the radiative lifetime of Kr₂F^* is 240±35 ns. The quenching rate constant for the coupled Kr(2p₈) and Kr(2p₉) levels by F₂ is (13±2)×10⁻¹⁰ cm³ s⁻¹.     

Ab initio CI study of the reaction between NH2 and NO

Using ab initio CI calculations we have evaluated the structural, energetic and kinetic parameters of the reaction between NH₂ and NO. In light of the results obtained, it appears that while the formation of molecular nitrogen is highly probable, the reaction pathway leading to N₂H+OH cannot be thermodynamically excluded. The kinetic model based on the RRKM and TST methods leads to a calculated rate constant at 298 K (k = 1.64×10⁻¹¹ cm³ molecule⁻¹ s⁻¹) which is comparable to that determined experimentally and which decreases with temperature in the range 200–700 K.     

Kinetics and mechanisms of the redox reaction of hexaaquotitanium(III) and the ethylenediamine tetraacetato titanium(III) complex by aqueous solutions of bromine

At 25°C, I = 1.0 M (CF₃SO₃⁻Li⁺+CF₃SO₃H), [H⁺] = 0.034–0.274 M and λ = 453 nm, the rate equation for the oxidation of Ti(H₂O), ₆³⁺ by bromine was found to be: −d/[Br₂]T/dt=kK/[Br₂][Ti^III]/[H⁺]+K+kK/[Br₃⁻][Ti^III]/[H⁺+K, where k = 9.2 × 10⁻³ M ⁻¹ s ⁻¹ and K = 4.5 × 10⁻³ M. At [H⁺] = 1.0 M, [Br⁻] = 0.05–0.4 M, the apparent second-order rate constant decreases as [Br⁻] increases.

The pH-dependence of the oxidation of Ti^III-edta by bromine is interpreted in terms of the change in identity of the Ti^III-edta species as the pH of the reaction medium changes. The second-order rate constants were fitted using a non-linear least-square computer program with (1/k₀^edta)² weighting into an equation of the form: k₀^edta =k₁+k₂K₁[H⁺]⁻¹+k₃K₁K₂[H⁺]^−2/1+K₁[H⁺[H⁺⁻¹+K₁K₂[H⁺]⁻², with K₁ and K₂ fixed as earlier determined at 9.55 × 10⁻³ and 2.29 × 10⁻⁹ M, respectively, for the oxidation of bromine. k₁=k₂=(3.1±0.32)×10³M⁻¹s⁻¹ k₃=(2.3±0.45)×10⁶N⁻¹s⁻¹.

It is proposed that these electron transfer reactions proceed by univalent changes with the production of Br₂^.− as a transient intermediate. An outer-sphere mechanism is proposed for these reactions. The homonuclear exchange rate for Ti^III-edta+Ti^IV-edta is estimated at 32 M⁻¹ s⁻¹.     

Temperature dependence of the rate constant for reactions of hydrated electrons with H, OH and H2O2

The temperature dependence of the rate constants, for the reactions of hydrated electrons with H atoms, OH radicals and H₂O₂ has been determined. The reaction with H atoms, studied in the temperature range 20–250°C gives k(20°C) = 2.4 × 10¹⁰M^-1s¹ and the activation energy E_A = 14.0 kJ mol^-1 (3.3 kcal mol^-1). For reaction with OH radicals the corresponding values are, k(20°C) = 3.1 × 10¹⁰M^-1s^-1 and E_A = 14.7 kJ mol^-1 (3.5 kcal mol^-1) determined in the temperature range 5–175°C. For reaction with H₂O₂ the values are, k(20°C) = 1.2 × 10¹⁰M^-1s^-1 and E_A = 15.6 kJ mol^-1 (3.7 kcal mol^-1) measured from 5–150°C. Thus, the activation energy for all three fast reactions is close to that expected for diffusion controlled reactions. As phosphates were used as buffer system, the rate constant and activation energy for the reaction of hydrated electron with H₂PO₄^- was determined to k(20°C) = 1.5 × 10⁷M^-1s^-1 and E_A = 7.4 kJ mol^-1 (1.8 kcal mol^-1) in the temperature range 20–200°C.     

Rate coefficients for the reactions of cyclohexadienyl (c-C6H7) radicals with O2 and NO at room temperature

Rate coefficients for the reactions of cyclohexadienyl (c-C₆H₇) radicals with O₂ and NO were measured at 296 ± 2 K. The c-C₆H₇ radicals were detected selectively by laser-induced fluorescence. The rate coefficient for the reaction of c-C₆H₇ with O₂, (4.4 ± 0.5) × 10⁻¹⁴ cm³ molecule⁻¹ s⁻¹, was independent of the bath-gas (He) pressure (13–80 Torr). In the reaction of c-C₆H₇ with NO, thermal equilibrium among c-C₆H₇, NO, and C₆H₇NO was observed. The forward and reverse reactions were in the falloff region, and the equilibrium constant was (1.5 ± 0.6) × 10⁻¹⁵ cm³ molecule⁻¹.     

Synthesis, crystal structure and third-order non-linear optical property of heterobimetallic cluster compound [MoOICu3S3(2,2′-bipy)2]

Nest-shaped cluster [MoOICu₃S₃(2,2′-bipy)₂] (1) was synthesized by the treatment of (NH₄)₂MoS₄, CuI, (n-Bu)₄NI, and 2,2′-bipyridine (2,2′-bipy) through a solid-state reaction. It crystallizes in monoclinic space group P2₁/n, a=9.591(2) Å, b=14.820(3) Å, c=17.951(4) Å, β=91.98(2)°, V=2549.9(10) ų, and Z=4. The nest-shaped cluster was obtained for the first time with a neutral skeleton containing 2,2′-bipy ligand. The non-linear optical (NLO) property of [MoOICu₃S₃(2,2′-bipy)₂] in DMF solution was measured by using a Z-scan technique with 15 ns and 532 nm laser pulses. The cluster has large third-order NLO absorption and the third-order NLO refraction, its ₂ and n₂ values were calculated as 6.2×10⁻¹⁰ and −3.8×10⁻¹⁷ m² W⁻¹ in a 3.7×10⁻⁴ M DMF solution.     

Rate constant of the reaction of NO3 with CH2I2 measured with use of cavity ring-down spectroscopy

We have applied cavity ring-down spectroscopy to a kinetic study of the reaction of NO₃ with CH₂I₂ in 25–100 Torr of N₂ diluent at 298 K. The rate constant of reaction of NO₃ + CH₂I₂ is determined to be (4.0 ± 1.2) × 10⁻¹³ cm³ molecule⁻¹ s⁻¹ in 100 Torr of N₂ diluent at 298 K. The rate constant increases with increasing pressure of buffer gas below 100 Torr. The reaction of CH₂I₂ with NO₃ has the potential importance at nighttime in the atmosphere.     

Kinetics and mechanism of the gas phase reaction of Cl atoms with iodobenzene

Smog chamber/FTIR techniques were used to study the kinetics and mechanism of the reaction of Cl atoms with iodobenzene (C₆H₅I) in 20–700 Torr of N₂, air, or O₂ diluent at 296 K. The reaction proceeds with a rate constant k(Cl+C₆H₅I)=(3.3±0.7)×10⁻¹¹ cm³ molecule⁻¹ s⁻¹ to give chlorobenzene (C₆H₅Cl) in a yield which is indistinguishable from 100%. The title reaction proceeds via a displacement mechanism (probably addition followed by elimination).