Louis J. Stief

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 parameters for the reaction of ground state atomic oxygen with carbonyl sulfide

The rate parameters for the reaction of O(3P) with carbonyl sulfide, O(3P) + OCS → CO + SO, (1) have been determined directly by monitoring O(3P) using the flash photolysis‐resonance fluorescence technique. The value for k1 was measured over a temperature range of 263–502°K and the data were fitted to an Arrhenius expression with good linearity, k1 = (1.65±0.13)×10−11 exp(−4305±55/R T) cm3 molecule−1·sec−1. A comparison of the present results with those from previous studies of Reaction (1) is also presented.

Branching ratios in the N + CH3 reaction - Formation of the methylene amidogen (H2CN) radical

The branching ratios for the reaction N+CH3 →Products, have been determined in a discharge‐flow system coupled with mass‐spectrometric detection of both reactants and products. The major products are H2 CN+H, with about 10% of the reaction proceeding to give HCN+H2 . Experiments carried out on the reaction of N atoms with the deuterated methyl radical showed that the branching ratio for formation of D2 CN+D is about 0.9 and for DCN+D2 formation about 0.1 independent of T from 200 to 363 K. The results are consistent with the energetics and orbital symmetry properties of the reactant and product molecules. Implications for the atmosphere of Titan are discussed.

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...

Pressure dependence of the absolute rate constant for the reaction OH+C2H2 from 228 to 413 K

The pressure dependence of absolute rate constants for the reaction of OH +C2H2→ products has been examined at five temperatures ranging from 228 to 413 K. The experimental technique which was used is flash photolysis–resonance fluorescence (FP–RF). OH was produced by water photolysis and hydroxyl resonance fluorescent photons were measured by multiscaling techniques. The results indicate that the low pressure bimolecular rate constant is ∼4×10−13 cm3 molecule−1 s−1 over the temperature range studied. A substantial increase in the bimolecular rate constant with an increase in pressure was observed at all temperatures except 228 K. This indicates the importance of initial adduct formation and subsequent stablization. The high pressure results are well represented by the Arrhenius expression (kbi)∞=(6.8.3±1.19)×10−12 exp(−646±47/T) cm3 molecule−1 s−1. The present results are compared to previous investigations and are theoretically discussed. The implications of these results on modeling of terrestrial and ...

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 Constant for the Reaction H+H2CO

The photolysis of formaldehyde in the pronounced absorption region ∼1700–1760 A has been investigated. The production of H atoms has been established by direct observation using pulsed photolysis and time dependent observation of the Lyman‐α resonance fluorescence at 1216 A. From the measurement of the H‐atom decay under pseudo‐first order conditions the rate constant for the reaction H+H2CO→ H2+HCO has been obtained. The result is 5.4± 0.5× 10−14 cm3 molecule−1· sec−1 at 297°K.

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.