Fritz S. Klein

Kinetic Isotope Effects in the Reaction between Atomic Chlorine and Molecular Hydrogen. Tunnel Coefficients of the Hydrogen Atom through an Asymmetric Potential Barrier

Kinetic isotope effects for the reactions between atomic chlorine and molecular hydrogen have been measured in the range of −30° to +70°C. The following expressions were obtained: RH2/HT=(1.27±0.03) exp[(797±14)/RT],RH2/D2=(1.44±0.06)exp[(1128±17)/RT],RH2/DT=1.534exp(1422/RT),RH2/T2=1.545exp(1693/RT).The isotope effect of HD, RH2/HD=(1.24±0.03) exp[(490±6)/RT], has been redetermined and found to agree with previous measurements.Theoretical calculations of these isotope effects, using (1) a Sato model, (2) a generalized Sato model, and (3) the Johnston—Parr method, were made to compare the calculated effects with experimental results.Tunnel corrections were applied using (1) an asymmetric Eckart barrier, or (2) the Johnston—Rapp method with an asymmetric barrier. Best agreement (within 15%) of calculated values with experiment was obtained for a generalized Sato model including Johnston—Rapp tunnel corrections. Empirical sets of four force constants describing the transition state H–H–Cl are also given. Th...

Force field and tunneling effects in the H--H--Cl reaction system. Determination from kinetic-isotope-effect measurements

An iterative method is used to obtain, within the framework of the transition state theory, sets of force constants from experimental kinetic‐isotope‐effect data for the reaction system H2 + Cl → [H–H–Cl]‡ → H+HCl. Two sets of force constants, describing quite different transition‐state structures, are found to be equally compatible with all available rate data for the reactions of chlorine atoms with H2, HD, HT, DT, D2, and T2. These force fields are compared with force fields derived by semiempirical methods. Measurements of the intramolecular kinetic isotope effect, i.e., the relative rate of production of HCl/DCl in the reaction HD+Cl, are shown to be especially suited for selecting compatible transition‐state models.

Deuterium‐Isotope Effect in the Chlorine Exchange between Hydrogen Chloride and Chlorine Atoms. A Study of Models for the Tunnel Effect

The rates of the exchange reactions of chlorine atoms with hydrogen chloride and with deuterium chloride were measured as a function of temperature. Chlorine atoms were produced by photodecomposition of chlorine gas and their relative concentration was monitored by their reaction with deuterium: Cl+D2→DCl+D. The temperature dependence of the logarithm of the ratio of rates was found to be nonlinear in the temperature range of 30° to 150°C. Various attempts to calculate the isotope effect assuming different types of tunneling are discussed.

Isotopic exchange reactions of atomic oxygen produced by the photolysis of NO2 at 3660 Å

Isotopically labelled atomic oxygen, produced by the photolysis of N18O2 at 3660 A, was allowed to react with CO, CO2, N2O, O2 and COCl2, respectively. The rates and mechanisms of the exchange reactions are discussed. The specific rate constants were determined for the process, O*+XO→O*X+O. They are 6.2 × 1010 exp [(–6900±700)/RT], 6.3 × 108 exp [(–3500±200)/RT], 9.6 × 108 exp [(–4400±800)/RT], and 3.9 × 109 exp [(–1100±400)/RT] 1. mole–1 sec–1 for CO, CO2, N2O and O2 respectively.

Reactive sputtering of simple condensed gases by keV heavy ion bombardment

Abstract Condensed layers of H2O, CO, NH3 and a mixture of H2O+CO have been bombarded by 3 keV Ar+ ions. Various newly formed molecules were sputtered and detected by mass spectrometry. To establish the chemical nature of the sputtered species these experiments have been performed with various stable isotopes. In order to prove that the detected fragment-ions did not originate from sputtered Van der Waals clusters, fragmentation patterns of various clusters as produced by a nozzle have been determined in situ. We could definitely establish sputtering of CO2 from CO; N2 and N2H4 from NH3; O2, OH and HO2 from H2O. From the mixture of H2O and CO the CO2 production was greatly enhanced as compared to that of pure CO. The oxygen atom released from H2O is chemically most active in this process. The sputtering yields of some molecules were very large. Energy distributions have also been measured, showing an asymptotic behaviour in agreement with a collision cascade model.

Competitive Reaction Rates of Hydrogen Atoms with HCl and Cl2. Entropy Considerations of the HCl2 Transition State

The relative rates of the reactions H+HCl→ lim k3H2+Cl and H+Cl2→ lim k6HCl+Cl, were determined in the temperature range of 0° to 62°C and found to be given by k3/k6=(0.143±0.033) exp−(1540±130/RT). The temperature‐independent factor in the above expression is interpreted in terms of the structure and the vibrational frequencies of the HCl2 transition state. The doubly degenerate bending frequency of this transition state is found to have a value of about 105 cm−1.

Temperature dependence of the intramolecular kinetic isotope effect in the reaction system Cl + HD

The relative rates of the two competing isotopic reactions, (1) Cl + HD → HCl + D and (2) Cl + DH → DCl + H were measured as a function of reaction temperature in the range of 297–443 °K. The ratio of rates can be expressed as an Arrhenius type equation; k1/k2 = (0.81 ± 0.04) × exp[(460 ± 50)/RT]. The very fast reaction of the hydrogen atoms formed with residual molecular chlorine, which under conventional experimental conditions would mask any isotope effect, was eliminated by adding NO2 as an efficient hydrogen atom scavenger to the stream of reactants in a fast flow reactor.

Ultraviolet‐Induced Isotope Exchanges in Gaseous Mixtures of HCl and D2 and of DCl and H2

Mixtures of HCl and D2 and of DCl and H2 were irradiated with an ultraviolet mercury resonance lamp and analyzed mass spectrometrically for the different isotopic species of hydrogen. It was found that at room temperature the reaction H+DCl→HD+Cl is slower than the exchange reaction H+DCl→D+HCl. This is to be expected from a consideration of activation energies, but it is in apparent contradiction to earlier results obtained by Leighton and Cross and by Steiner and Rideal. The reaction between hydrogen atoms and hydrogen molecules was found to be much faster at this temperature than is usually estimated.

Ion cyclotron resonance study of the gas-phase ion chemistry of the carbonyl halides: Cl2CO, F2CO and ClFCO

Abstract The gas-phase ion chemistry of Cl2CO, F2CO and ClFCO has been studied by ion cyclotron resonance mass spectrometry. The relative abundance of the primary negative ions X−, X2−, and XCO− (X  F or Cl) formed by electron impact, have been measured. The electron energy dependence of the dissociative electron attachment cross sections for the negative ion formation have been determined. In phosgene negative ions are formed at near thermal energies, while in F2CO and ClFCO resonance maxima were found between 1.5 and 3.5 eV. Negative ion-molecule reactions leading to the formation of secondary COX3− ions were observed in all three compounds. The mechanism of these reactions, determined by double resonance techniques, was found to be a halide ion transfer. The relative rates of these reactions were determined by pressure dependence measurements. Lower limits for the heats of formation of the secondary negative ions COX3− were calculated. The relative abundances of the positive ions formed by electron impact of 70 V electrons were determined. No positive ion-molecule reactions were observed.

Ion-Molecule chemistry in formaldehyde by ion cyclotron resonance mass spectrometry

Abstract The ion—molecule reactions taking place in gaseous monomeric formaldehyde under electron impact have been studied by ion cyclotron resonance techniques. The main reaction product at low pressures is the secondary ion CH 3 O + , which is formed by proton transfer from either of the two primary ions, CH 2 O + or CHO + , to the neutral formaldehyde molecule. At higher pressures a number of proton transfer and hydrogen abstraction reactions are observed involving additional fragment ions producing secondary and tertiary ions, such as CH 4 O + CH 5 O + , CH 2 + and CH 3 + . At still higher pressures, product ions containing two carbon atoms are formed by complex reactions. The identity of all ions was verified by use of deuterium and 18 O-labelled formaldehyde. Double resonance techniques were applied to confirm the reaction channel and to determine some of the reaction mechanisms. Relative rate constants of the main reactions were measured.