The rate of the reactions of C2O radicals with H and H2

The rate constants for the reactions C₂O + H → products (1) and C₂O + H₂ → products (2) have been determined at room temperature by means of laser-induced fluorescence detection of C₂O radicals, generated either by the KrF excimer laser photolysis Of C₃O₂, or by the reaction of C₃O₂ with O atoms. Values of k₁ = (3.7 ± 1.0) × 10^?11 cm³ s^?1 and k₂ = (7 ± 3) × 10^?13 cm³ s^?1 were obtained.     

Kinetics of the reaction of NH2 with NO2

The absolute rate constant of the reaction of NH₂ with NO₂ has been measured using a flash-photolysis laser resonance-fluorescence technique. The value obtained at room temperature is k₁ = 2.3 (± 0.2) × 10^?11 cm³ molecule ^?1 s^?1. A negative temperature coefficient has been found between 298 and 505 K for this reaction, k₁ = 3.8 × 10^?8 × T^?1.30 cm³ molecule^?1 s^?1. It is thought that this is the major reaction of NH₂ in the troposphere.     

Absolute Rate constants for O + No + N2 → NO2 + N2 from 217–500 K

Flash photolysis of NO coupled with time resolved detection of O via resonance fluorescence has been used to obtain rate constants for the reaction O + NO + N₂ → NO₂ + N₂ at temperatures from 217 to 500 K. The measured rate constants obey the Arrhenius equation k = (15.5 ± 2.0) × 10^?33 exp(1160 ± 70)/1.987 T] cm⁶ molecule^?2 s^?1. An equally acceptable equation describing the temperature dependence of k is k = 3.80 × 10^?27/T^1.82 cm⁶ molecule^?2 s^?1. These results are discussed and compared with previous work.     

Kinetics of the association of H+3 with H2 at low temperatures

The rate constant for the formation of H⁺₅ (D⁺₅) at (86 ± 3) °K by the three-body process has been determined (k₃(H) = (2.16 ± 0.10) × 10^?28 × 10^?28 cm⁶/molecule² sec and k₃(D) = (1.47 ± 0.20) × 10^?28 cm⁶/molecule² sec) in a high pressure mass spectrometer. Comparison of this result with published rate data at 300 °K indicates the reaction has an apparent activation energy of ?1.5 kcal/mole.     

Rate coefficients for CS reactions with O2, O3 and NO2 AT 298 K

CS radicals have been produced by photodissociation of CS₂ at 193 nm and their disappearance monitored by LIF. The vibrationally excited CS radicals rapidly relax to CS(ν = 0). At 298 K, the rate coefficients for CS(ν = 0) reactions with O₂, O₃ and NO₂ are (2.9 ± 0.4) × 10_?19, (3.0 ± 0.4) × 10^?16 and (7.6 ± 1.1) × 10^?17 cm³ molecule^?1 s^?1 respectively. The quenching of CS(A ¹II)_ν=0 by He has a rate coefficient of (1.3 ± 0.2) × 10^?12 cm³ molecule^?1 s^?1.     

Upper limits for the rate constant for the reaction Br + H2O2 → HBr + HO2

Upper limits for the rate constant for the reaction Br + H₂O₂ → HBr + HO₂ have been measured over the temperature range 298 to 417 K in a discharge flow, system using a mass spectrometer as a detector. Results are K₁< 1.5 × 10^?15 cm³ s^?1 at 298 K and K₁< 3.0 × 10^?15 cm³ s^?1 at 417 K, respectively. The implication to Stratospheric chemistry is discus     

Oscillator strengths of the bands of the B̃2 A′1—X̃2 A″2 system of CD3 and a spectroscopic measurement of the recombination rate comparison with CH3

Absolute CD₃ concentrations were measured in the flash photolysis of d₆-HgMe₂. An oscillator strength of (0.99 ± 0.10) × 10^?2 was recorded for the 0O band of the B?—X? system, and a recombination rate coefficient of (4.9 ± 0.4) × 10^?11 cm³ molecule^?1 s^?1 was derived. It is suggested that the probability of recombination per collision is virtually the same as for the CH₃ radical.Some new bands of the B?—X? system have been discovered and tentatively assigned: from a study of the temperature dependence of the intensity of the 47300 cm^?1 transition, Herzberg's scheme ‘b’ has been established for the vibrational assignment.     

Reactions of HO2 with NO,OH and HO2 studied by EPR/LMR spectroscopy

A combined EPR/LMR spectrometer and fast-flow system has been used to investigate the reactions HO₂ + NO(k₁), HO₂ + OH(k₂), HO₂ + HO₂(k₃) at room temperature. The rate constants have been measured: k₁ = (7.0 ± 0.6) × 10^?12 cm³ s^?1 (P = 7–10 Torr);k₂ = (5.2 ± 1.2) × 10^?11 cm³ s^?1 (P = 8–10 Torr);k₃ = (1.65 ± 0.3) × 10^?12 cm³ s^?1 (P = 2.1–24.9 Torr). The conclusion is drawn from analysis of the literature and the present work that k₂ and k₃ do not depend on pressure up to 1 atm.     

The mechanism of SO2 oxidation by CH3O2 radicals. Rate coefficients for the reactions of CH3O2 with SO2 and NO

The reactions of CH₃O₂ with SO₂ and NO have been studied by steady state photolysis of azomethane in the presence of O₂SO₂→NO mixtures at 296 K and 1 atm total pressure. The quantum yield of NO oxidation by CH₃O₂ radicals is increased substantially when SO₂ is added to the system indicating an SO₂ induced chain oxidation of NO. The rate law gives k₁/k₂ = (2.5 ± 0.5) × 10^?3 for CH₃O₂ + SO₂ → CH₃O₂SO₂ (1), CH₃O₂ + NO → CH₃O + NO₂ (2). Combining this ratio with the absolute value of k₁ = 8.2 × 10^?15 cm³ s^?1 gives k₂ = 10^{?11.5 ± 02} cm³ s^?1.     

The time-resolved LMR method as used to measure elementary reaction rates of CI atoms and SiH3 radicals in pulse photolysis of S2Cl2 in the presence of SiH4

The time-resolved laser magnetic resonance (LMR) method has been applied to kinetic measurements for the first time. An intracavity spectrometer based on a CO₂ laser with resonant modulation of the magnetic field and with phase-sensitive detection of the signal has been used. Kinetic curves of generation and disappearance of CI atoms and SiH₃ radicals were obtained in the pulse photolysis of a mixture of S₂Cl₂ + SiH₄ under the fourth harmonic of a Nd laser (265 nm, 0.5 mJ, 12.5 Hz) at a total pressure of 520–980 Pa (he as diluent) and a temperature of 326 K. The reagent concentrations were: [S₂Cl₂ = (2.0?10.2)×10¹⁴ cm^?3, [SiH₄ = (2.4?17.4)×10¹³ cm^?3. To remove the transition saturation, 5.3×10¹⁵ cm^?3 CCl₄ was introduced into the reactor. The fraction of dissociated S₂Cl₂ was 1‰ Rate constants of the reactions (I) Cl+S₂Cl₂ → products, (II) Cl+SiH₄ → HCl+SiH₃ and a preliminary rate constant of the reaction (III) SiH₃ + S₂Cl₂ → products were obtained: k₁ ≤ (4.3±1.2)×10^?12 cm³/s, k₂ = (2.3±0.5)×10^?10 cm³/s, k₃ = (2.4±0.5)×10^?11 cm³/s. At a signal-to-noise ratio of 1:1, 1000 pulses and a 12 cm long detection zone the sensitivity to Cl atoms and to SiH₃ radicals was 4×10¹⁰ cm^?3 and = 10¹¹ cm^?3, respectively. The time resolution of the method was 4 μs. The method is shown to be promising for kinetic investigations and experiments on fast processes.     

Reactive and non-reactive quenching of O(1D2) by COF2

Quenching of O(¹D₂) by COF₂ has been investigated by time-resolved resonance fluorescence monitoring of the product O(³P_J) following 248 nm pulsed laser photolysis of O₃. The rate constant for total removal of O(¹D₂) by COF₂ is (7.4 ± 1.2) × 10^?11 cm³ molecule^?1 s^?1. 71 ± 7% of the quenching interactions result in formation of O(³P^J).     

Kinetics of the reactions OH (v = O) + NH3 →; H2O + NH2 and OH(v = O) + O3 → HO2 + O2 AT 298°K

The rate constants for the reactions OH(X₂Π, ν = O) + NH₃ → ^k1 H₂O + NH₂ and OH(X²Π, ν = O) + O₃^k2 → HO₂ + O₂ were measured at 298°K by the flash photolysis resonance fluorescence technique. The values of the rate constants thus obtained are K₁ = (4.1 ± 0.6) × 10^?14 and k₂ = (6.5 ± 1.0) × 10^?14 in units of cm³ molecule ^?1 sec¹. The results are discussed in terms of understanding the dynamics of the perturbed stratosphere.     

The temperature dependence of the HO2 + HO2 reaction

The temperature dependence of the rate constant for the reaction HO₂ + HO₂ → H₂O₂ + O₂ (2k₁) has been determined using flash photolysis techniques, over the temperature range 298–510 K, in a nitrogen diluent at a total pressure of 700 Torr. The overall second order state constant is given by k₁ = (4.14 ± 1.15) × 10^?13 exp[(630 ± 115)/T] cm³ molecule^?1 s^?1, where the quoted errors refer to one standard deviation. This result is compared with previous findings and the negative activation energy is shown to be consistent with the observation that the rate constant is pressure dependent at 700 Torr.     

Rate constant for the reaction NH3 + OH → NH2 + H2O over a wide temperature range

The rate constant for the reaction or NH₃ + OH → NH₂ + H₂O has been measured in a high temperature fast flow reactor over the range 294–1075 K k = (5.41 ± 0.86) × 10^-12 exp[?(2120 ± 143) cal mole^?1/RT cm³ molecule^?1 s^?1. This result is compared with literature values and discussed.     

Deuterium isotope effect in the T1 → S0 radiationless transition of propynal in the gas phase

The phosphorescence lifetimes of propynal-h₁ and propynal-d₁ have been measured at room temperature in the 40 mTorr-1 Torr pressure range The reciprocal of the zero-pressure lifetime (k₀) is (3.10 ± 0.05) × 10³ and (1.70 ± 0.04) × 10³ s^?1 for propynal-h₁ and propynal-d¹ For both compounds the rate constant for self-quenching between triplet and ground-state molecules is k_SQ = (1 2±007) × 10³ Torr^?1 s^?1 The deuterium isotope effect is attributed to the T₁ → S₀ radiationlcss decay, for which k^H_ISC/k^D_ISC = 2 4     

The collisional quenching of O2*(1Δg) by NO and CO2

Rate coefficients for the collisional quenching of O₂^*(¹Δ_g) by NO and CO₂ at 2–8 torr and 300 K have been determined. k_NO = (2.48 ± 0.23) × 10^?17 cm³ molecule^?1 s^?1 and

= (2.56 ± 0.12) × 10^?18 cm³ molecule^?1 s^?1.     

The 1B1u ← 1A1g 0—0 transition in crystal benzene

The transition linewidth ΔE in crystal C₆H₆, C₆D₆ and sym-C₆H₃D₃ has been measured as a function of temperature T from 4.2 to 135°K, and it extrapolates to a common value of ΔE_o = 50 cm^? at O°K. In C₆H₆ ΔE = (50 + 7T^{$\text{1}\text{2}$}) cm^?1, indicative of strong exciton—phonon coupling, and there is a line shift of +40 cm^?1 per substituent deuteron. Fluorescence excitation spectral data are used to separate the ¹B_1u(= S₂) decay rate k_H = 9.4 × 10¹² sec^?1, derived from ΔE₀, into S₂S₁ internal conversion (rate ≈ 6.6 × 10¹² sec^?1) and S₂S_x (channel 3) internal conversion (rate ≈ 2.8 × 10¹² sec^?1. A similar value of k_H = 9.9 × 10¹² sec^?1 is obtained from the S₂S_o fluorescence quantum yield of liquid benzene.     

Ternary association reactions leading to formation of CH+3·(H2O)n in the energy range 0.04–0.1 eV

The ion-molecule reaction CH₃⁺ + H₂O has been studied with a drift tube apparatus. The first step of the reaction was found to have a third-order rate constant with a negative temperature coefficient: k_He⁽³⁾ = 1.3 × 10^?26 (T/300)^?3.3 and K_w⁽³⁾ = 1 × 10^?24 (T/300)^?0.85. Both water molecules and helium atoms act as stabilizing third bodies.     

Temperature dependence of the reaction rate constants for O(3P) atoms with C2H4, C3H6 and NO(M = N2O), determined by a modulation technique

Rate constants for the reaction of O(³P) atoms with C₃H₄, C₃H₆ and NO(M = N₂O) have been measured over the temperature range 300–392°K using a modulation-phase shift technique. The Arrhenius expressions obtained are:C₂H₄, k₂ = 3.37 × 10⁹ exp[?(1270 ± 200)/RT]liter mole^?1 sec^?1,C₃H₆, k₂ = 2.08 × 10⁹ exp[?(0 ± 300)/RT]liter mole^?1 sec^?1,NO(M = N₂O), k₁ = 9.6 × 10⁹ exp[(900 ± 200/RT]liter² mole^?2 sec^?1.These temperature dependencies of k₂ are in good agreement with recent flash photolysis-resonance flourescence measurements, although lower than previous literature values.     

Rates of reaction of NH2 with N,NO AND NO2

The decay of NH₂ radicals, from 193 nm photolysis of NH₃, was monitored by 597.7 nm laser-induced fluorescence. Room-temperature rate constants of (1.21 ± 0.14) × 10^?10, (1.81 ± 0.12) × 10^?11, and (2.11 ± 0.18) × 10^?11 cm³ molecule^?1 s^?1 were obtained for the reactions of NH₂ with N, NO and NO₂, respectively. The production of NH in the reaction of NH₂ with N was observed by laser-induced fluorescence at 336.1 nm.