Denis J. Bogan

Internal energy of hydroxyl radicals desorbing from polycrystalline Pt surfaces

Abstract The internal energy distribution of OH radicals desorbing from a polycrystalline Pt surface at 1130 K was measured by laser-induced fluorescence at pressures near collisionless conditions. Both the rotational and vibrational temperatures are equal to that of the Pt, suggesting that the rate of energy randomization of OH with the surface is greater than the rate of desorption.

Dynamics of hydroxyl radical desorption from a polycrystalline platinum surface

Laser‐induced fluorescence was used to determine the internal energy distribution of OH radicals desorbing from a polycrystalline Pt surface at T = 1130 K. The measurements were performed in a low‐pressure flow system under conditions which were shown to be nearly collisionless by determining the energy distribution as a function of pressure. A Cu surface surrounding the reaction zone removed OH radicals efficiently and prevented scattering back into the laser beam. Both the rotational and vibrational temperatures were found to be equal to that of the Pt catalyst, suggesting that the product OH reaches thermal equilibrium with the surface at a rate which is greater than the rate of desorption. For the systems investigated (H2+O2, H2+NO2, H2O), the energy distributions were independent of the source of OH radicals.

FORMATION AND CHEMILUMINESCENT DECOMPOSITION OF DIOXETANES IN THE GAS PHASE

Abstract— High resolution chemiluminescence spectra have been obtained of the singlet electronically excited products of O2(1Δ) plus alkene, dioxetane forming, reactions. The experiments were conducted in a flow apparatus at pressures of 1–5 torr. The spectra are a measure of the unrelaxed initial distribution of energy in the excited product. Results are reported for ethylene, 1, 1‐difluoroethylene. methyl vinyl ether, ethyl vinyl ether, n‐butyl vinyl ether, ketene, ketene‐d2, allene, unsymdimethyl allene, dimethyl ketene, 2‐methoxy propene, 1‐ethoxy propene, 2‐bromo propene, and N, N‐dimethyl isobutenyl amine. Chemiluminescence activation energies, representing the cycloaddition process, and absolute quantum yields for singlet excited product, ranging from 10‐‐4 to 2.5 × 10‐‐2. are reported for 10 alkenes. Several of the reactions, 1,1‐difluoroethylene, ketene, ethylene and allene give formaldehyde 1nπ* product with excess vibrational‐rotational energy and a higher quantum yield than reactions not displaying this phenomenon. This is an indication of at least partially statistical partitioning of the energy in excess of that needed to electronically excite the formaldehyde. The experiments with ketene and ketene‐d2 provide the first evidence for the existence of unsubstituted 1,2‐dioxetanone. The results from several of the experiments, particularly those with 2‐methoxy propene and I‐ethoxy propene are consistent with the mechanism of Goddard, which predicts regioselective and stereoselective attack of O2(1Δ) upon alkoxy substituted alkenes having allylic hydrogen.

Observation of O2(b 1Σg+ → X 3Σg−) chemiluminescence from the self-reaction of isopropylperoxy radicals

Abstract We report the first direct observation of singlet oxygen product resulting from a gas phase self-reaction of alkylperoxy radicals. The evidence is a rotationally resolved O2(b 1Σg+ → X 3Σg−) chemiluminescence spectrum observed in a 12 l integrating sphere reactor containing less than 1014 isopropylperoxy radicals per cubic centimeter diluted in helium and O2 at a total pressure of 80 Pa (0.6 Torr). According to a mechanism proposed by Russell in 1957, the self-reactions of non-tertiary alkylperoxy radicals proceed by formation of a weakly bound dialkyl tetraoxide intermediate which can decompose to yield a carbonyl, an alcohol and O2. There are five energetically accessible product state potential energy surfaces. Spin conservation forbids the ground state products, but allows the formation of O2 in the 1Σg+ or 1Δg states or of T1 carbonyl. We claim these results to be strong evidence for the occurrence of Russells mechanism in the gas phase.

Simple and reliable system for gas flow regulation and measurement

An automatic regulation and measurement system for the delivery of gases at flow rates from about 0.01 to 1 cm3 (STP)/s is described. Flow measurement is based on the familiar direct method of determining pressure drop per unit time in a calibrated volume. The regulation and measurement functions are accomplished by simple electronic circuits. Pressure drop from the primary gas supply to the delivery point occurs in two stages. In the first stage, gas is admitted to the calibrated volume by a solenoid valve that can be opened for times as short as 10−3 s. In the second stage the gas flows through a needle valve to the delivery point. The pressure in the calibrated volume is measured by a transducer. The circuit reads the transducer output and regulates the pressure by controlling the frequency and duration of the solenoid valve opening. The fluctuations in delivered gas flow are typically ±0.5%, and could be made much smaller with modest effort. This sytem has several advantages over commercial ‘‘mass flo...

Quantitative product study of russell termination reactions of peroxy radicals in the gas phase

Detailed product patterns have been obtained from flowing alkylperoxy radical mixtures by cryogenic trapping of the total gas stream, followed by analysis. A discharge flow reactor was used, and initiation of the reaction sequence was by O(3P) or Cl(2P) atoms. R H + O → R · + O H ( a 1 ) R H + C l → R · + H C l ( a 2 ) The gas composition was >98% O2, 1% RH and R R ′ C H · + O 2 → R R ′ C H O O · ( a 3 ) 2 R R ′ C H O O · → 2 R R ′ C H O · + O 2 ( a 4 ) 2 R R ′ C H O O · → R R ′ C = O + R R ′ C H O H + O 2 ( a 5 ) R R ′ C H O · → R C H O + R ′ · ( a 6 ) The β-scission reaction, a6, consumes virtually all alkoxy, hence carbonyl and alcohol products having the unaltered carbon skeleton of the RH reactant (≥50% of all products) were assigned exclusively to termination by reaction a5. Experiments were done in mixed primary and/or secondary and/or tertiary systems, and quantitative structural isomer analyses obtained. These establish that the formation mechanism for the unfragmented carbonyls and alcohols involves a peroxy radical dimer. An independent experiment showed the presence of O2(1Σ→3Σ) chemiluminescence which we attribute to termination by a5, in the isopropylperoxy system. It is claimed that these results are conclusive evidence for the occurrence of termination reaction, a5, by the concerted Russell mechanism: Download : Download full-size image