Frank P. Tully

Hydrogen-atom abstraction from alkenes by OH, ethene and 1-butene

Abstract Absolute rate coefficients for the reactions of the hydroxyl radical with ethene ( k 1 ), ethene- d 4 ( k 2 ), 1-butene ( k 3 ), and 1-butene- d 8 ( k 4 ) were measured over the temperature range 650–901 K. The rate coelTlcient data, in the units cm 3 molecule −1 s −1 , are fitted to the Arrhenius equations k 1 ( T ) = (3.36 ±0.64) × 10 −11 exp[-(5955 ± 287) cal mol −1 / RT ], k 2 ( T ) = (5.85 ± 1.54) × 10 −11 exp[-(7816±407) cal mol−1/ RT ], k 3 ( T ) =(3.74±0.63) × 10 −11 exp[-(2217±243) cal mol-1/ RT ], and k 4 ( T )= (3.56 ± 0.25) × 10 −11 exp [-(2730 ± 98) cal mol −1 / RT ], in which the stated error limits are 2σ values. These data are compared with previous results, and kinetic isotope effects are discussed.

Laser photolysis/laser-induced fluorescence study of the reaction of hydroxyl radical with ethylene☆

Abstract A new, laser-based chemical kinetics technique has been demonstrated in studies of the reaction of OH with C2H4. The reaction mechanism is dominated by electrophilic addition of OH to the double bond at low temperatures, and by increasingly rapid decomposition of the thermalized adduct HOC2H4 back to reactants as the temperature is raised.

Kinetic study of the hydroxyl radical-propene reaction

Abstract Absolute rate coefficients for the reactions of OH with C 3 H 6 and C 3 D 6 were measured at temperatures from 293 to 896 K and at pressures from 25 to 600 Torr helium. Mechanistic information of importance to atmospheric and combustion modeling was obtained.

Kinetic study of the reaction between CN and O2 from 295 to 710 K

Abstract We have extended the highly precise laser photolysis/cw laser-induced fluorescence technique to the study of CN-radical reaction kinetics. We investigated the reaction of CN with O2 over the temperature range 295–710 K. The measured reaction-rate coefficients are well represented over this temperature range by the two-parameter Arrhenius expression, k=(1.24±0.04) × 10−11 exp[(1630±100) J mol−1/RT] cm3 molecule−1 s−1, where the quoted uncertainties represent ± 2σ estimates of the total experimental error. NCO forms as a direct product of the reaction.

Catalytic conversion of alcohols to alkenes by OH

Abstract Kinetic and mechanistic studies of the gas-phase reactions between hydroxyl radicals and Cn alcohols (n⩾2) are described. Hydrogen-atom abstraction by OH from β-sites in alcohols produces HO-alkene intermediates that rapidly dissociate to OH + alkene at elevated temperatures. This reactive sequence consitutes a catalytic mechanism for the net transformation CnH2n+1OH→ H2O + CnH2n. The fraction of OH-alcohol reactivity that proceeds through this catalytic channel depends on the detailed molecular structure of the alcohol.

CH+H2 reaction kinetics: Temperature and pressure dependence and Rice–Ramsperger–Kassel–Marcus‐master‐equation calculation

We investigate the reaction of CH(X 2Π) with H2 as a function of temperature in the range 240–470 K at 8.2 and 750 Torr of helium pressure and as a function of helium pressure in the range 8–750 Torr at 294 K. Methylidyne forms upon excimer‐laser photolysis of CHBr3 or CHClBr2 in a slow‐flow reactor and we time‐resolve its concentration profile using cw laser‐induced fluorescence. The title reaction proceeds through the formation of an excited methyl radical with multiple open decay channels. We observe dramatically different temperature dependencies at high and low helium bath‐gas pressures. At high pressure, collisional stabilization of CH*3 to CH3 dominates the reaction mechanism and the CH‐loss rate constant exhibits a negative temperature dependence over the range studied. At low pressure, the predominant product channel switches from CH3 to CH2+H as the temperature increases. We employ a Rice–Ramsperger–Kassel–Marcus‐master‐equation calculation to model the experimental results.

Hydrogen-atom abstraction from alkanes by OH. I. Neopentane and neooctane

Absolute rate coefficients for reactions of the hydroxyl radical with neopentane, perdeuteroneopentane, and neooctane were measured with the laser photolysis/laser-induced fluorescence technique. Experiments were performed at 400 torr helium pressure over the temperature range 287–903 K. The data were fit to modified Arrhenius expressions of the form k(T)=ATn exp (−E/RT). From this study, it was found that common parameters could be used to characterize the kinetics of the three reactions. For the OH/neopentane system, an increase in the reaction activation barrier of ≈947 cal/mole resulted upon deuterium substitution in neopentane. Theoretical calculations of this energy shift were performed and excellent agreement with experiment was obtained.

Free-radical oxidation of isocyanic acid

Laser-based kinetic studies of the reactions OH+HNCO→Products (1) and O( 3 P)+HNCO→Products (2) are described. Deuteration of isocyanic acid demonstrates that hydrogen-atom abstraction is an important channel for reaction (1). The kinetic results may be represented by the Arrhenius expressions k 1 (T)=(4.4±0.9)×10 −12 exp [−(5.54±.28) kcal mol −1 /RT] cm 3 molecule −1 s −1 and k 2 (T)=5.4×10 −12 exp [−10.3 kcal mol −1 /RT] cm 3 molecule −1 s −1 . The mechanistic implications of these results on the RAPRENO x process are discussed.

Exalite 392E: a new laser dye for efficient cw operation between 373 and 408 nm

Exalite 392E is found to offer significant improvements in the preparation of dye solutions for efficient ultraviolet dye lasers./AIP/.

Catalytic dehydration of alcohols by OH. (H3C)3CCH2OH: A limiting case

We describe a laser-photolysis/laser-induced-fluorescence kinetic study of the reaction between OH and neopentyl alcohol, (H3C)3CCH2OH, over the temperature range 293–764 K. The experiments test our model of catalytic dehydration of alcohols by OH, proving that s-site hydrogen atoms must exist in the alcohol if the conversion alcohol→H2O+alkene is to occur efficiently. We achieve separation of reactivity among the (H3C)3- and CH2OH-sites, and find that kCH2OH exhibits a surprising temperature dependence. A minor channel that reforms OH at long times exists, and we present a phenomenological characterization of its kinetics.