Richard W. Fox

Bio: Richard W. Fox is an academic researcher from Cooperative Institute for Research in Environmental Sciences. The author has contributed to research in topics: Photodissociation & Reaction rate constant. The author has an hindex of 2, co-authored 2 publications receiving 24 citations.

Reaction of Hydroxyl Radical with Nitric Acid: Insights into Its Mechanism†

Abstract: The rate constant for the reaction of hydroxyl radicals with nitric acid has an unusual pressure and temperature dependence. To explore the mechanism for this reaction, we have measured rate constants for reactions of isotopically substituted species OD + DNO3, OH + DNO3, OD + HNO3, and 18OH + HNO3 and the yield of NO3 product. Deuterium substitution on nitric acid results in more than a 10-fold reduction in the rate constant, removes the pressure dependence (over the observed range of 20−200 Torr in He and SF6), and leads to a strongly curved Arrhenius temperature dependence. Deuterium substitution on hydroxyl increases the rate constant slightly but does not change the pressure dependence. There is no evidence for exchange reactions in the isotopically mixed reactions. Absorption measurements of the NO3 product yield show that the title reaction produces nitrate radical with unit efficiency over all temperatures and pressures studied. We discuss the implications of the measured rate constants, product y...

Cluster Ion Reactions: Insights into Processes of Atmospheric Significance

Abstract: Experimental results of ion cluster reactions withatmospherically relevant species are considered hereinto provide a unified overview of the current state ofunderstanding brought about through experimentalstudies of cluster ion reactions. This isaccomplished by first outlining the atmospheric issuesaddressed by cluster ion studies and then, summarizingthe results of numerous studies. The recent, as wellas previously published studies of cluster ionreactions, are considered in the context of gainingnew insights into the molecular details ofheterogeneous processes involving the interactions ofelectrolytes with cloud droplets, ice crystals andaerosol particles. In addition to elucidating themechanisms of these and other selected reactions andtransformations of atmospheric significance, thefindings of the uptake of acid molecules in waterclusters are shown to lead to the suggestion of a newmodel that accounts for the formation of reactioncenters involving charged sites at aqueous surfaces.

Reaction of OH with HO2NO2 (Peroxynitric Acid): Rate Coefficients between 218 and 335 K and Product Yields at 298 K

Abstract: Rate coefficients (k 3 (T)) for the reaction of OH with HO 2 NO 2 (peroxynitric acid, PNA) in the gas phase were measured in the temperature range of 218-335 K by producing OH via pulsed laser photolysis and detecting it via laser-induced fluorescence. The PNA concentration was measured in situ by UV and IR absorption. The H 2 O 2 , HNO 3 , and NO 2 impurities present in the PNA sample were quantified by mass spectrometry and/or UV/IR absorption. The measured value of k 3 (298 K) is (3.4 ′ 1.0) x 10 - 1 2 cm 3 molecule - 1 s - 1 . The temperature dependence of k 3 is best described by the relation k 3 (T) = (8.8 ′ 2.6) × 10 - 1 9 T 2 exp[(1130 ′ 20)/T] cm 3 molecule - 1 s - 1 . The quoted errors for k 3 are at the 2σ level and include estimated systematic errors, which contribute the most to this uncertainty. The measured values of k 3 (T) were independent of pressure between 10 and 100 Torr of helium. The branching ratios of the reaction OH + HO 2 NO 2 → products, for the production of HO 2 and HNO 3 and of NO 3 and H 2 O 2 , respectively, were determined to be <10% and <5%, respectively, at 298 K. Thus, it was deduced that the main pathway for reaction 3 produces H 2 O, O 2 , and NO 2 at 298 K. Our measurements reduce the uncertainties but do not significantly alter the currently calculated impacts of HO 2 NO 2 in the upper troposphere and lower stratosphere. In the course of this study, the rate coefficient for the reaction of OH with H 2 O 2 was measured to be k 4 (T) = (2.9 ′ 1.8) × 10 - 1 2 exp[-(110 ′ 150)/T] cm 3 molecule - 1 s - 1 in the temperature range of 273-356 K.

Photodissociation of brono2 and n2o5 : quantum yields for no3 production at 248, 308, and 352.5 nm

Abstract: Quantum yields for NO3 production in the photolysis of BrONO2 and N2O5 were measured at 248, 308, and 352.5 nm. The measured values for BrONO2 were found to be independent of pressure over the range 150−600 Torr and bath gas (N2 or O2) and are 0.28 ± 0.09, 1.01 ± 0.35, and 0.92 ± 0.43 at 248, 308, and 352.5 nm, respectively. Quantum yields of Br and BrO in the photolysis of BrONO2 were also estimated. The measured values for NO3 production in the photolysis of N2O5 were 0.64 ± 0.10, 0.96 ± 0.15, and 1.03 ± 0.15 at 248, 308, and 352.5 nm, respectively. Rate coefficients for the reactions Br + BrONO2 → Br2 + NO3 (18) and Cl + BrONO2 → ClBr + NO3 (19) were measured at 298 K to be k18 = (6.7 ± 0.7) × 10-11 cm3 molecule-1 s-1 and k19 = (1.27 ± 0.16) × 10-10 cm3 molecule-1 s-1. The NO3 product yields for reactions 18 and 19 were measured to be 0.88 ± 0.08 and 1.04 ± 0.24, respectively. The absorption cross sections for N2O5 between 208 and 398 nm are also reported. All quoted uncertainties are 2σ and include es...

A kinetic study of chlorine radical reactions with ketones by laser photolysis technique

Abstract: Rate coefficients for reactions between CI radicals and four ketones were determined at 294 +/- 1 K with a relative rate method using a laser photolysis technique. The experiments were conducted in ...