Kyle D. Bayes

CO Chemiluminescence from Flames

The chemiluminescence from the reaction of oxygen atoms and carbon suboxide in a flow system has been reinvestigated. In addition to the “triplet” bands reported previously, two other band systems of CO were observed: the Herman bands, also in the red, and the Fourth Positive bands in the vacuum ultraviolet. The three electronic states show a common excitation limit of almost 9 eV above the ground state. The emission intensity in the red and in the vacuum ultraviolet vary together as the flame conditions are changed, showing that the three excited states are formed in a single reaction. Traces of hydrogen are not necessary for the chemiluminescence. The reaction responsible for the emission is probably O(3P) + C2O(X 3Σ)→CO(A 1Π, d 3Δ, e 3Σ) + CO(X 1Σ). Quenching of the CO emission depends on the ratios (NO) / (O) and (O2) / (O). NO is a more efficient quencher than O2, in agreement with the behavior found for C2O(X 3Σ) formed by the photolysis of C3O2. The vacuum‐ultraviolet emission from a O + C2H2 flame...

Rates of reaction of butyl radicals with molecular oxygen

Rate constants for the reaction of four different butyl radicals with molecular oxygen have been measured at room temperature. The radicals were generated by flash photolysis and their time decay was followed with a photoionization mass spectrometer. The radical concentrations were kept low to avoid complications from radical–radical reactions. Radical lifetimes were long, up to 50 msec, thus assuring that thermalized radicals were being studied. The rate constants, in units of 10−11 cm3 molecule−1 sec−1, are: n‐butyl (0.75±0.14); s‐butyl (1.66±0.22); t‐butyl (2.34±0.39); 3‐hydroxy s‐butyl (2.8±1.8). No pressure dependence of the rate constants was observed over the range 1 to 4 Torr. In the absence of O2, the butyl radicals decay mainly by loss on the quartz surface of the reaction cell, with sticking coefficients in the range of 10−2 to 10−3. The Adiabatic Channel Model can predict the approximate absolute values of these rate constants using reasonable molecular parameters, but it fails to reproduce th...

Direct determination of the equilibrium constant and thermodynamic parameters for the reaction. C3H5+ O2⇌ C3H5O2

The reaction of allyl radicals with oxygen has been studied using argon fluoride laser flash photolysis coupled with ultraviolet absorption detection. At temperatures between 382 and 453 K it was possible to observe directly the establishment of equilibrium between allyl, oxygen and allyl peroxy (C3H5+ O2⇌ C3H5O2). From analysis of the allyl radical decay signals the temperature dependences of both the forward and reverse rate constants, k1 and k–1, were obtained. The temperature dependence of the equilibrium constant, Kp=k1/(k–1RT) gave a value for ΔS⊖298 of –(122 ± 5) J mol–1 K–1 and for ΔH⊖298 of –(76.2 ± 2.1) kJ mol–1. The equilibrium constants were shown to be pressure-independent, although both k1 and k–1 were below their high-pressure limits. Above 453 K the form of the decay and the apparent value of the equilibrium constant deviate from the lower-temperature behaviour because of the onset of an additional reaction channel.

Photolysis of nitrogen dioxide

Relative quantum yields for the photolysis of NO2 to give NO have been measured at 5 or 10 nm intervals in the range of 295 to 445 nm, and also at several longer wavelengths. The behavior of the quantum yield as a function of photon energy can be separated into three distinct wavelength regions. At all wavelengths shorter than 398 nm the quantum yield is almost constant and independent of NO2 pressure in the range 0.5–4 torr. Hence, by comparison with previous work, the photodissociation probability of NO2 remains close to unity for photolysis by all wavelengths shorter than the dissociation limit at 398 nm. At wavelengths longer than 430 nm, there is a small quantum yield for NO formation which decreases slowly with increasing wavelength. Quenching studies and variations in light intensity show that these small yields are caused by reaction of an electronically excited NO2 molecule with ground state NO2. In the wavelength region between 400 and 430 nm, the quantum yield falls abruptly. Isotopic exchange ...

Rate constants for CH(X 2Π) reactions at low total pressures

Abstract Rate constants for the reactions of CH(X 2 Π) with N 2 , O 2 , N 2 O, H 2 , D 2 and H were measured under pseudo- first-order conditions at 297 K and 2 Torr total pressure. CH (X 2 Π) radicals were generated by excimer laser photolysis (248 nm) of CH 2 Br 2 /Ar and CHClBr 2 /Ar mixtures and detected by laser-induced fluorescence (LIF). The values obtained (cm 3 s −1 ) are: k N 2 = (8.0 ± 0.6) × 10 −14 , k O 2 = (5.1 ± 0.3) × 10 −11 , k N 2 O = (6.9 ± 0.9) × 10 −11 , k H 2 = (2.0 ± 0.3) × 10 −12 , k D 2 = (1.7 ± 0.4) × 10 −11 and k H = (1.4 ± 0.5) × 10 −11 .

Measuring rate constants for reactions of the simplest Criegee intermediate (CH2OO) by monitoring the OH radical.

While generating the CH2OO molecule by reacting CH2I with O2, significant amounts of the OH radical were observed by laser-induced fluorescence. At least two different processes formed OH. A fast process was probably initiated by a reaction of vibrationally hot CH2I radicals. The second process appeared to be associated with the decay of the CH2OO molecule. The addition of molecules known to react with CH2OO increased the observed decay rates of the OH signal. Using the OH signals as a proxy for the CH2OO concentration, the rate constant for the reaction of hexafluoroacetone with CH2OO was determined to be (3.33 ± 0.27) × 10(-11) cm(3) molecule(-1) s(-1), in good agreement with the value measured by Taatjes et al.1 The rate constant for the reaction of SO2 with CH2OO, (3.53 ± 0.29) × 10(-11) cm(3) molecule(-1) s(-1), showed no pressure dependence over the range of 50-200 Torr and was in agreement with the value at 4 Torr reported by Welz et al.

Spectroscopic Study of the Chemiluminescent Reaction O + CCO

Further spectroscopic studies of the chemiluminescence from oxygen atom–acetylene and oxygen atom–carbon suboxide flames are reported. The reaction18 O + CC16O→C18O + C16O results in the emission of Fourth Positive bands by both C18O and C16O with comparable intensities, suggesting that the intermediate OCCO exists for at least several vibrations. Some bands in the d 3Δ→X 1Σ+ system are identified. Partially resolved rotational structure of the Fourth Positive bands show irregular intensities which are interpreted as strong emission from perturbed rotational levels. It is concluded that the reaction forming excited CO in hydrocarbon flames populates the A 1Π, d 3Δ, e 3Σ−, I 1Σ−, and a′ 3Σ+ states of CO at comparable rates. Possible reactions of the metastable CO molecules are suggested.

Kinetic isotopic fractionation and the origin of HDO and CH3D in the solar system

It is argued that photochemical processes, driven by ultraviolet starlight, could lead to large deuterium fractionation for H2O and CH4 relative to H2 in the primitive solar nebula. Implications for deuterium enrichment observed in planetary atmospheres are briefly discussed.

The rate of reaction of methyl radicals with atomic oxygen

Abstract The absolute rate constant for the reaction of ground state oxygen atoms with methyl radicals is reported. The methyl radicals were generated by the reaction of oxygen atoms with ethylene in a fast flow reactor, and were detected by a photoionization mass spectrometer. For sufficiently long reacton times, the methyl radicals were observed at their steady state concentration. For shorter reaction times, especially at low oxygen atom concentrations, the methyl radical concentration was less than the steady state value. From the observed approach of the methyl radicals totheir steady state concentration, the rate constant for the reaction, O + CH 3 , was determined to be (1.23 ± 0.25) × 10 −10 cm 3 molecule −1 sec −1 , corresponding to one reaction in every two gas kinetic collisions.

Kinetics of C2O radicals formed in the photolysis of carbon suboxide at 308 and 248 nm

Abstract The photolysis of carbon suboxide (C 3 O 2 ) at 248 and 308 nm was investigated by monitoring laser-induced fluorescence (LIF) of the product C 2 O(X 3 Σ − ). At 308 nm the C 2 O(X 3 Σ − ) appears immediately after the photolysis flash followed by a slow decay. This clean source of C 2 O(X 3 Σ − ) was used to measure rate constants for reactions with O 2 and CO and to set an upper limit on its reactivity with CO 2 . Measurements were also made of rate constants for the quenching of C 2 O(A 3 Π i ) by N 2 , SF 6 , CO and CO 2 . At 248 nm the LIF signal starts at a small value and increases for several hundred microseconds before decaying. Both the maximum intensity of the LIF signal and its rate of rise can be increased by adding CO. It is concluded that photolysis at 248 nm initially forms one of the low-lying singlet states of C 2 O, probably a 1 Δ, and that most of this singlet state is lost by reaction with C 3 O 2 . CO has the unique ability to convert the singlet state of C 2 O to the X 3 Σ − state by intersystem crossing on the attractive C 3 O 2 surface. A semiquantitative model for this system has been proposed and its agreement with the experimental results is discussed.