Myron Kaufman

The rate of homogeneous recombination of fluorine atoms

Abstract The recombination rate of fluorine atoms has been determined in a Teflon-coated flow reactor at 295°K and pressures of 10–81 torr with Ar as the carrier gas. Concentrations of atomic fluorine are measured by titrating with Cl 2 and using the intensity of chlorine atom recombination emission as an endpoint indicator. The data is fit with a third-order homogeneous recombination rate constant of 2.9 × 10 13 cm 6 /mole 2 sec. Possible systematic errors in the titration lead us to claim only a factor of two accuracy for the result. The measured rate constant is ca. a factor of 10 less than values calculated by two different theories and ca. a factor of 100 less than the accepted rate constants for homogeneous recombination of most other atoms under similar conditions.

Principles of Thermodynamics

Introduction and Background Thermodynamics: The Zeroth and First Laws The Second Law of Thermodynamics The Third Law and Free Energies Statistical Mechanics Phase Transformations in Single-Component Systems Chemical Reactions Ideal Solutions Nonideal Solutions Ionized Systems Surfaces Steady-State Systems Appendix A Multivariable Calculus Appendix B Numerical Methods Appendix C Tables of Thermodynamic Data Appendix D Glossary of Symbols Index

Kinetics of the reaction of bromine atoms with molecular fluorine

The rate constant of the reaction of bromine atoms with molecular fluorine is determined by mass spectrometrically monitoring BrF produced at fixed reaction time as a function of the concentration of F2 added to a flowing mixture of Br and Br2 in He diluent. The rate constant is 1.31×10−13 exp(−17.9 kJ mole−1/RT) cm3 molecule−1 sec−1 over the temperature range 296–418° K. Br+F2 is thus another example of the anomalously slow rate which is characteristic of the reactions of F2 with many atoms.

Kinetics studies relevant to possible coupling between the stratospheric chlorine and sulfur cycles

Abstract In order to probe possible coupling between the stratospheric chlorine and sulfur cycles, the kinetics of the reactions of Cl and ClO with SO 2 and SCO are investigated in a fast-flow reactor with mass spectrometric monitoring of reactants and products. For the reaction Cl + SO 2 + M → ClSO 2 + M over the temperature range 266–331 K, k = (2.2 ± 1.8) × 10 −34 exp [(1240 ± 1050)/ RT ] and (9.9 ± 8.1) × 10 −34 exp [(1770 ± 970)/ RT ] cm 6 molec −2 s −1 with Ar and SO 2 as third bodies, respectively. The room temperature rate constant for the reaction Cl + SCO → SCl + CO appears to be between 10 −18 and 10 −16 cm 3 molec −1 s −1 . Neither of these reactions are significant for stratospheric chlorine chemistry. No reactions are observed between ClO and SO 2 and SCO. The upper limits which we can place on the rate constants for these reactions, however, do not completely rule out their importance for stratospheric chlorine chemistry.

Rate constant of the reaction between chlorine atoms and sulfur dioxide and its significance for stratospheric chlorine chemistry

Abstract The rate constant of the reaction Cl + SO2 + M → ClSO2 + M is measured in a fast-flow reactor with mass spectrometric monitoring of chlorine atoms and product Cl2SO2. At 295K, k = 1.3± 0.9,2.3±0.5 and 19±3 × 10 − 33 cm6molec − 2s − 1,withAr,N2,andSO2as third bodies respectively.Ifstratospheric [SO2] is as low as 2 × 10 − 10 v/v , this reaction is probably not an important sink for stratospheric chlorine in our atmosphere, although it may have greater significance in the atmosphere of Venus.

Some Novel Diagnostic Techniques for Plasma Chemistry

Abstract In order to probe the mechanisms of chemical transformations in electric discharges it is most useful to monitor concentrations of reactants, products and reactive intermediates as a function of discharge parameters. Mass spectrometry, a popular technique for observing intermediates in chemical reactions, meets with particular difficulty when applied to discharges, due to the presence of excited molecules as well as free radicals in such systems. Molecular beam analysis, a synthesis of mass spectrometry with molecular beam measurements of electric and magnetic moments and velocity distributions, is a technique developed in our laboratory which offers distinct advantages for the analysis of intermediates in electric discharges. In low pressure discharges, end-product analysis can be facilitated by sample compression. A chromatographic sampling system which employs compression in order to achieve high sensitivity has been developed and evaluated. There is some question concerning the appropriate discharge parameters to be employed in correlating measured variations in concentrations. We are investigating the use of discharge “actinometers” as a means of measuring the intensity of electric discharges. In discharges the intensity (number and energy of the electrons) and the chemistry are strongly coupled. Thus, it is necessary that the actinometer be present in the reactor; it is not permissible to substitute vessels as is customary in photochemical investigations. Since the actinometer is to measure only the discharge intensity, it must not participate in any chemical reactions with molecules and intermediates in the discharge. Finally, the ratio of the rates of the primary interactions of the actinometer and reactant with the discharge must be independent of discharge parameters.

Coal liquefaction in a fluorocarbon medium. 1. Nitrogen compounds as hydrogen transfer agents

Abstract Coal processed in a perfluorocarbon liquid at 250 °C with low concentrations of additives may undergo chemical reactions, but does not dissolve. Under these conditions quinoline has little effect on coal, while 1,2,3,4-tetrahydroquinoline produces marked increases in coal solubility, presumably due to hydrogen donation. While the hydrogen requirements of a bituminous coal are satisfied by tetrahydroquinoline at a tetrahydroquinoline: coal ratio of 0.2, for a lignitic coal, addition of gaseous hydrogen is necessary for substantial solubility increase.

Luminescence from hydrogenfluorine flames, dilute in methane☆

Abstract Mechanisms producing luminescence from CH, C 2 , and CHF in CH 4 F 2 flames are studied by the method of very dilute flames, whereby small amounts of CH 4 (below 2%) are added to H 2 F 2 flames. This technique allows the dependence of the emission intensities on the concentration of CH 4 and carbon-containing radicals to be separated from its dependence on equivalence ratio and pressure, which determines flame temperature and the concentration of hydrogen and fluorine atoms. The most likely mechanism for C 2 emission is the reaction of two CH radicals, while CH emission (both A and B states) and CHF emission probably result from vibration-to-electronic (V-E) energy transfer from vibrationally excited HF. Experiments using CD 4 and D 2 are in agreement with the mechanism proposed for CH emission. The isotope experiments, as well as laser-induced fluorescence measurements on CH, indicate that the V-E energy transfer is by a single step, rather than by stepwise excitation up the vibrational ladder of CH(X). A diagnostics for the [F] [F 2 ] ratio in F 2 H 2 or F 2 hydrocarbon combustion is suggested. The mechanisms proposed for CH and C 2 luminescence are different from those generally discussed for the same emissions in oxygen-supported combustion.

Combustion of hydrocarbons in purified fluorine

Abstract Emission spectra and ionization are compared in premixed flames of CH 4 burning in commercial F 2 (0.4% O 2 ) with those burning in purified F 2 . Oxygen impurity is reduced to below 0.02% in the purified F 2 by reaction with SbF 5 . No appreciable differences exist between the spectra of flames burning in commercial and purified F 2 ; both are dominated by bands of CHF and CH. CH emission is thus an intrinsic property of F 2 -hydrocarbon combustion. In contrast, ionization (as measured by a Langmuir probe) is reduced to an undetectable level in flames with purified F 2 and is roughly proportional to O 2 concentration in flames with unpurified F 2 . Ionization is thus not an inherent property of F 2 -hydrocarbon combustion.

Recombination emission in hydrogen-fluorine systems

Abstract Visible emission which is generated when H 2 is added to partially dissociated F 2 is found to be due to Δυ = 4, 5, and 6 transitions of HF(X). The temporal and stoichiometric dependence of this emission strongly suggests that it results from direct combination of hydrogen and fluorine atoms and/or from recombination of hydrogen atoms with subsequent transfer of vibrational energy from H 2 to HF.