R. B. Klemm

Rate constants for the reaction of hydroxyl radicals with acetaldehyde from 244--528 K

The rate constant for the reaction of hydroxyl radical with acetaldehyde OH+CH3CHO → products has been measured from 244–528 K with the discharge flow‐resonance fluorescence technique. The temperature dependence, expressed in Arrhenius form, is k1(T)=(5.52±0.80)×10−12 exp(610±103/RT) cm3 molecule−1 s−1, where R is in cal mol−1 and the errors are at the two standard deviation level. This result is compared to earlier flash photolysis‐resonance fluorescence work. Mechanistic considerations are additionally discussed, and it is concluded that acetyl radicals are the most probable products of the reaction. Lastly, theoretical calculations are presented which delineate theoretical issues to be addressed in ab initio potential energy calculations.

Rate constant for the reaction of O(3P) with H2 by the flash photolysis—shock tube and flash photolysis—resonance fluorescence techniques; 504K≤T≤2495K

The rate constant for the reaction, O ( P 3 ) + H 2 → O H + H , ( 1 ) was measured over the temperature range of 504K to 2495 K by two independent experimental methods. The flash photolysis-shock tube (FP-ST) technique, combined with atomic resonance absorption spectroscopy (ARAS), was used over the temperature range 880K to 2495K. The results from the FP-ST work, expressed in simple Arrhenius form, are: k 1 ( T ) = ( 3.1 ± 0.2 ) × 10 − 10 exp ⁡ ( − 13620 ± 170 / R T ) c m 3 molecule − 1 s − 1 , where the units of R in this and succeeding expressions are cal mole −1 K −1 . The flash photolysis-resonance fluorescence (FP-RF) technique was utilized to measure rate constants from 504K to 923K. Results from the FP-RF experiments, also expressed in simple Arrhenius form, are: k 1 ( T ) = ( 7.2 ± 0.4 ) × 10 − 11 exp ⁡ ( − 10430 ± 70 / R T ) c m 3 molecule − 1 s − 1 . These kinetic results for the reaction of O( 3 P) with H 2 exhibit non-Arrhenius behavior. This conclusion is confirmed by the recent kinetic data of Presser and Gordon (297K≤T≤471K). The combined results from these three data sets are expressed by the three parameter fit: k 1 ( T ) = 8.4 × 10 − 20 T 2.67 exp ⁡ ( − 6290 / R T ) c m 3 molecule − 1 s − 1 . The estimated error in this expression is about ±30% over the entire temperature range, 297K to 2495K. Rate constants for reaction (1) from recent ab initio calculations are in excellent agreement with these experimental results.

Rate constant and reaction channels for the reaction of atomic nitrogen with the ethyl radical

The absolute rate constant and primary reaction products have been determined at T=298 K for the atom–radical reaction N(4S)+C2H5 in a discharge flow system with collision‐free sampling to a mass spectrometer. The rate constant measurements employed low energy electron impact ionization while the product study used dispersed synchrotron radiation as the photoionization source. The rate constant was determined under pseudo‐first‐order conditions by monitoring the decay of C2H5 or C2D5 as a function of time in the presence of excess N atoms. The result is k=(1.1±0.3)×10−10 cm3 molecule−1 s−1. For the reaction product experiments using photoionization mass spectrometry, products observed at 114 nm (10.9 eV) were CD3, D2CN and C2D4 for the N+C2D5 reaction. The product identification is based on the unambiguous combination of product m/z values, the shift of the m/z peaks observed for the N+C2D5 reaction products with respect to the N+C2H5 reaction products and the photoionization threshold measured for the ma...

Absolute rate constant for the reaction of O(3P) with CH3SCH3 from 272 to 472 K

Rate constants for the oxidation reactions of organic sulfur compounds have become increasingly important due to their potential role in the formation of tropospheric and stratospheric sulfate aerosols. The present study deals with the reaction of the ground state oxygen atom with dimethyl sulfide. A discharge fast flow–resonance fluorescence technique was used to follow the decay of O(3P) atoms in the presence of excess CH3SCH3 under pseudo‐first‐order conditions. Kinetic data, obtained over the temperature range 272 to 472 K, are well represented by the Arrhenius expression, kbi= (1.28±0.12) ×10−11 exp[(803±60)/RT] cm3 molecule−1 sec−1. The results are compared to those of previous studies which employed different experimental techniques.

A discharge flow‐photoionization mass spectrometric study of HOBr(X 1A’): Photoion yield spectrum, ionization energy, and thermochemistry

The photoion yield spectrum of HOBr was measured over the wavelength range λ=108–121 nm by using a discharge flow‐photoionization mass spectrometer apparatus coupled to a synchrotron radiation source. HOBr was generated by the reaction of OH with molecular bromine. A value of (10.62±0.04) eV was obtained for the adiabatic ionization energy (I.E.) of HOBr from photoion thresholds, corresponding to the HOBr+(2A‘)←HOBr(1A’) transition. The structure observed in the spectrum is discussed in terms of the available states for HOBr+, which have been determined using multiconfiguration‐self‐consistent field calculations. A new value for ΔH0f 298(HOBr) of −9 kcal mol−1 is derived from I.E.(HOBr) and estimates of ΔHf(HOBr+).

Comment on “A study of HeI photoelectron spectroscopy on the electronic structure of the nitrate free radical NO3” [J. Chem. Phys. 106, 3003 (1997)]

The recent photoelectron spectroscopy (PES) paper by Wang, et al. confirms our earlier photoionization mass spectrometric (PIMS) determination of the adiabatic ionization energy of NO3. The PES results are also consistent with our conclusion that the ground-state neutral geometry for NO3 is D3h. However, the PE spectrum shows a second band (and higher bands) with a vertical I.E. (ionization energy) at 13.18 eV that was absent in our photoionization efficiency spectrum. A possible reason for the apparent discrepancy is suggested and further differences between the two studies are discussed.

A resonance fluorescence kinetic study of oxygen atom+hydrocarbon reactions, V:O(3P)+neopentane (415–922 K)

Absolute values of the rate constants for the reaction of O( 3 P) with neo-C 5 H 12 were determined directly with the use of the complementary techniques: flash photolysis (FP) and discharge flow (DF). The O-atoms were monitored via resonance fluorescence (RF) in both systems, allowing experiments to be carried out at very low [O]. Secondary reactions were averted in this way, and the rate data thus obtained were stoichiometry-free. The DF-RF experiments were performed over the temperature range, 427–922 K while those with the FP-RF apparatus were performed from 415–528 K. Over the common range of temperature the absolute rate constants were in excellent agreement. The combined set of data from 415–922 K is well described by k 1 =(1.52±0.28)×10 −10 exp (−7143±196/RT) cm 3 molecule −1 s −1 where R is expressed in cal mole −1 K −1 and the errors are taken at the two standard deviation level (95% confidence). The bond energy-bond order (BEBO) method along with activated complex theory was applied to the title reaction, and satisfactory agreement with experimental rate constants was obtained.