R. Bruce Klemm

Absolute rate parameters for the reactions of formaldehyde with O atoms and H atoms over the temperature range 250–500 K

Absolute rate coefficients for the reaction of H atoms and O atoms with formaldehyde were determined over the temperature range of 250 to 500 K. Linear Arrhenius behavior was observed in log(ki) vs 1/T plots for both reactions and the following rate parameters were obtained: k1(T) = (3.27±1.61) ×10−11 exp (−3670±365/RT) cm3 molec−1 s−1, k2(T) = (2.78±0.32) ×10−11 exp (−3030±80/RT) cm3 molec−1 s−1. Indicated error limits are two standard deviations. These results are compared with those of previous studies and are further discussed in terms of extrapolation to higher temperatures.

Evaluation of the rate constant for the reaction OH+H2CO: Application of modeling and sensitivity analysis techniques for determination of the product branching ratio

Novel modeling and sensitivity analysis techniques are used with experimental data obtained from discharge flow–resonance fluorescence experiments to evaluate the product branching ratio of OH+H2CO. Two channels are considered: the H‐atom abstraction reaction (R2) to form HCO and H2O; and the addition reaction (R17) followed by rearrangement and decomposition to form HCOOH and H. The rate constant values obtained at 298 K are kR2 =(7.75±1.24)×10−12 cm3/molecule s and kR17=(0.2+0.8−0.2) ×10−12 cm3/molecule s. The results demonstrate that the reaction proceeds almost exclusively via the H‐atom abstraction pathway.

Absolute rate parameters for the reaction of O(3P) with H2CO over the temperature range 250 to 750 K

Absolute rate constants for the reaction of ground state oxygen atoms with formaldehyde were determined over the temperature range 298 to 748 K using the discharge flow‐resonance fluorescence technique. The results were combined with rate data from a flash photolysis‐resonance fluorescence study (250 to 498 K) of this reaction to obtain an Arrhenius expression that is linear from 250 to 748 K: k1(T) = (2.94±0.26) ×10−11 exp  (−3065±67/RT) cm3 molecule−1 s−1. This result is compared with those of previous studies and possible kinetic complications are discussed in terms of a detailed mechanism. The significance of an extrapolation of this determination of k1 to higher and lower temperatures is also discussed.

Rate constants for the reaction of ground state atomic oxygen with methanol

The reaction of O(3P) with methanol has been studied using the complementary discharge flow and flash photolysis techniques. In both cases, resonance fluorescence detection of atomic oxygen was employed. The discharge flow (DF) apparatus was used in a temperature range of 298–998 K while the flash photolysis (FP) apparatus was used in the overlapping range of 329–527 K. The apparent bimolecular rate constants for the O‐atom/methanol reaction obtained from DF experiments at low temperatures (T?450 K) were independent of both the initial O‐atom concentration and the mode of O‐atom production. In addition, large excesses of O2 were added to the flow to intercept the primary reaction product (CH2OH), but had no apparent effect on the measured rate constant. Results from the two methods were in good agreement within this limited temperature range (∼300–500 K). At temperatures above ∼450 K, the apparent rate constants obtained from DF experiments were increasingly sensitive to the O2 concentration, with the rat...

Rate constants for the reaction, O(3P)+H2O¶OH+OH, over the temperature range 1053 K to 2033 K using two direct techniques

The rate constant for the reaction of O( 3 P) with H 2 O (reaction (1)) was measured over the temperature range 1288 K≤T≤2033 K using the flash photolysis-shock tube technique and at 1053, 1090 and 1123 K using the flash photolysis-resonance fluorescence method. The photolytic source for O( 3 P) atoms was nitric oxide. The results were given by the Arrhenius expression: k 1 (T)=(9.2±0.9)×10 −11 exp(−19100±300 cal mol −1 /RT) cm 3 molecule −1 s −1 The present results were equally well fit to the three parameter expression: k 1 (T)=4.93×10 −18 T 2.02 exp(−13400 cal mol −1 /RT) cm 3 molecule −1 s −1 . Uncertainties in the Arrhenius expressions are given at the one standard deviation level and the mean deviation of the data from each expression is ±16%. Corresponding rate constants for the reverse reaction (reaction (−1)) were computed from the known values of the equilibrium constant and were fitted to the Arrhenius equation: k −1 (T)=(8.9±0.9)×10 −12 exp(−2100±300 cal mol −1 /RT) cm 3 molecule −1 s −1 . These direct experimental results for k −1 (T) and k 1 (T) are compared with previously reported experimental measurements and with available theoretical expressions.

A discharge flow-photoionization mass spectrometric study of the FO(X 2 Pi i) radical. Photoionization efficiency spectrum and ionization energy

Photoionization efficiency spectra of FO were measured over the wavelength range 80.0–100.0 nm and in the ionization threshold region, 94.0–100.0 nm, using a discharge flow-photoionization mass spectrometer apparatus coupled to a synchrotron radiation source, FO was generated by the reaction of F(2P) atoms with NO3 and via a F2/O2 discharge. A value of 12.78 ± 0.03 eV was obtained for the adiabatic ionization energy of FO from photoion thresholds which corresponds to FO+ (X 3∑−) ← FO(X 2Πi). These results, which are the first to be obtained by direct PIMS measurements, corroborate those of a photoelectron spectroscopy study; however, the ionization energy determined here is free from interferences due to other species which complicated the PES measurement. A value of 109.5 ± 8.0 kJ mol−1 for ΔfH0298(FO) is computed from the present value of IE(FO) and a previous appearance energy measurement, and a value for the proton affinity of FO is calculated to be 511.5 ± 10.0 kJ mol−1.