W. A. Payne

A flasch photolysis–resonance fluorescence study of the formation of O(1D) in the photolysis of water and the reaction of O(1D) with H2, Ar, and He −

The relative importance of two primary processes in the photolysis of water, H2O+hν → H+OH d in Processes I and II, respectively. The initially formed O(1D) was deactivated to ground state O(3P) prior to detection via resonance fluorescence. The relative quantum yields for Porcesses I and II are 0.89 and 0.11 for the wavelength interval 105–145 nm and ?0.99 and ?0.01 for the wavelength interval 145–185 nm. Rate constants at 300 °K have been determined relative to that for Reaction (1), O(1D)+O2 → O(3P)+O2 decrease in O signal as a function of H2, Ar, or He pressure for the following reactions: O(1D)+H2 → H+OH % (2), O(1D)+Ar → O(3P)+Ar e−1⋅s−1, we obtain the following results: %k2 = (2.5±1.5) ×10−10, k3 = (8±4) ×10−13, and k4 < 5×10−14 cm3 molecule−1⋅s−1.

Absolute rate constant for the reaction of atomic hydrogen with acetylene over an extended pressure and temperature range

The technique of flash photolysis coupled with time resolved detection of H via resonance fluorescence has been used to obtain absolute rate parameters for the reaction of atomic hydrogen with acetylene, i.e., H+C2H2?C2H3* (1); C2H3*+M→C2H3+M (2). The rate constant for the reaction is strongly pressure dependent and was measured over the pressure range 10 to 700 torr. The reaction was also studied as a function of temperature over the range 193 to 400 °K and the high pressure limit of the rate constant at each temperature was used to obtain the Arrhenius expression k1= (9.63±0.60) ×10−12 exp(−2430±30/1.987T) cm3 molecule−1⋅sec−1. The present results are compared with those of previous studies.

Absolute rate of the reaction of N(4S) with NO from 196–400 K with DF–RF and FP–RF techniques

Rate constants for the reaction of N(4S) with NO have been measured from 196–400 K with two independent techniques both which utilize resonance fluoresence detection for temporal analysis of N(4S). The reaction has been studied at 196, 297, and 370 K by the discharge flow‐resonance fluorescence technique (DF‐RF) and the measured rate constant is best represented by the temperature independent value of (2.7±0.4) ×10−11 cm3 molecule−1 s−1. The technique of flash photolysis‐resonance fluorescence (FP‐RF) has been used to study the reaction at 233, 298, and 400 K, and the results are best represented by the temperature independent value of (4.0±0.2) ×10−11 cm3 molecule−1 s−1. Combination of the results suggests a value of (3.4±0.9) ×10−11 cm3 molecule−1 s−1 between 196–400 K. In this work discrimination between O(3P) atom and N(4S) atom fluorescence was necessary, and this was accomplished by inclusion of an O atom resonance line filtering section as an integral part of the resonance lamp. The suggested value...

Absolute rate constants for the reaction of atomic hydrogen with ketene from 298 to 500 K

Rate constants for the reaction of atomic hydrogen with ketene have been measured at room temperature by two techniques, flash photolysis–resonance fluorescence (FP–RF) and discharge flow–resonance fluorescence (DP–RF). The measured values are (6.19±1.68) ×10−14 and (7.3±1.3) ×10−14 cm3 molecule−1 s−1, respectively. In addition rate constants as a function of temperature have been measured over the temperature range 298–500 K by the FP–RF technique. The results are best represented by the Arrhenius expression k= (1.88±1.12) ×10−11 exp(−1725±190/T) cm3 molecule−1 s−1, where the indicated errors are at the two standard deviation level. These results are compared to two previous investigations both of which employed the discharge flow–mass spectrometric technique. Also they are compared to the analogous reaction, H+C2H4 (high pressure limit) since both reactions refer to addition across a carbon–carbon double bond. The reaction is considered theoretically from the activated complex point of view. Lastly, the...

Rate constants for the reaction of atomic chlorine with methanol and dimethyl ether from 200 to 500 K

Absolute rate constants for the reaction of atomic chlorine with dimethyl ether and methanol, Cl+CH3OCH3→HCl+CH2OCH3 (1),Cl+CH3OH→HCl+CH2OH (2), have been measured over the temperature range 200–500 K, using the flash photolysis–resonance fluorescence technique. In both systems, the results were independent of substantial variations in reactant concentration, total pressure (Ar) and flash intensity (i.e., initial [Cl]). The rate constants were also shown to be invariant with temperature. The best representation for this temperature range was found to be k1= (1.76±0.15) ×10−10 cm3 molecule−1 s−1 and k2= (6.33±0.70) ×10−11 cm3 molecule−1 s−1, respectively, where the error is one standard deviation. These are the first determinations of the rate constants for Reactions (1) and (2). These reactions are theoretically discussed and compared to the related reactions of Cl with CH4, C2H6, and H2CO. Molecules of the type CH3OX (where X=H, OH, etc.) are likely to be formed in the stratosphere as products of the oxi...

Absolute rate of the reaction of atomic hydrogen with ethylene from 198 to 320 K at high pressure

The rate constant for the H+C2H4 reaction has been measured as a function of temperature. Experiments were performed with high pressures of Ar heat bath gas at seven temperatures from 198 to 320 K with the flash photolysis–resonance fluorescence (FP–RF) technique. Pressures were chosen so as to isolate the addition rate constant k1. The results are well represented by the Arrhenius expression k1= (3.67±0.66) ×10−11 exp(−1040±42/T) cm3 molecule−1 s−1 (quoted errors are two standard deviations). The results are compared with other studies and are theoretically discussed.

Absolute rate of the reaction of Cl(2P) with methane from 200–500 K

Rate constants for the reaction of atomic chlorine with methane have been measured from 200–500 K using the flash photolysis–resonance fluorescence technique. When the results from 14 equally spaced experimental determinations are plotted in Arrhenius form a definite curvature is noted. The results are best represented by a statistically evaluated least squares three‐parameter fit given by k=5.44×10−19 T2.50 exp(−608/T) cm3 molecule−1 s−1. Over the range 299–500 K, the data are well represented by the Arrhenius expression k= (18.4±2.8) ×10−12 exp(−1545±52/T) cm3 molecule−1 s−1, while the corresponding expression for the 200–299 K range is k= (6.51±0.79) ×10−12 exp(−1229±27/T) cm3 molecule−1 s−1. The error limits are the standard deviations of the least squares fit.. The results are compared to previous work and are theoretically discussed.

Rate constant for the reaction of hydroxyl radical with formaldehyde over the temperature range 228–362 K

Absolute rate constants for the reaction OH+H2CO have been measured over the temperature range 228–362 K using the flash photolysis–resonance fluorescence technique. The results were independent of variations in [H2CO], total pressure [Ar] and flash intensity (i.e., initial [OH]). The rate constant was found to be invariant with temperature in this range, the best representation being k1?0.11)×10−11 cm3 molecule−1 s−1 where the error is two standard deviations. This result is compared with previous absolute and relative determinations of k1. The reaction is also discussed from a theoretical point of view.

Absolute rate of the reaction of hydrogen atoms with ozone from 219-360 K

Absolute rate constants for the reaction of atomic hydrogen with ozone were obtained over the temperature range 219–360 K by the flash photolysis–resonance fluorescence (FP–RF) technique. The results can be expressed in Arrhenius form by k = (1.33±0.32) ×10−10 exp(−449±58/T) cm3 molecule−1 s−1 (two standard deviations). The present work is compared to two previous determinations and is theoretically discussed.

Absolute rate of the reaction of O(3P) with hydrogen sulfide over the temperature range 263 to 495 K

The technique of flash photolysis coupled with time resolved detection of O via resonance fluorescence has been used to obtain rate constants for the reaction of O(3P) with H2S at temperatures from 263 to 495 K and at pressures in the range 10–400 torr. Under conditions where secondary reactions are avoided, the measured rate constants for the primary step obey the Arrhenius equation k= (7.24±1.07) ×10−12 exp(−3300±100/1.987 T) cm3 molecule−1 sec−1. The results are discussed and comparisons are made with previous work and theoretical predictions. Experiments with D2S show that the reaction exhibits a primary isotope effect, in support of a hydrogen abstraction mechanism.