Paul Goldfinger

Mass spectrometric and Knudsen-cell vaporization studies of group 2B-6B compounds

The vaporization of the nine compounds of Zn, Cd and Hg with S, Se and Te has been investigated by mass spectrometry. The typical process is the decomposition into gaseous metal atoms and diatomic group 6B molecules. Small amounts of polymeric species of sulphur were observed in the vapour above HgS and considerable amounts of polymeric selenium molecules above HgSe; HgTe yields Hg(g) and solid Te. No gaseous group 2B-6B molecules were observed; their concentration is below 1 part in 103-105. Estimates of dissociation energies are made and the possibility of observing these molecules is discussed. Decomposition pressures of all nine compounds were measured by the Knudsen method and corresponding enthalpy and entropy data deduced and compared with literature data. The heat of vaporization of lead has been remeasured. The heats of atomization of the group 2B-6B compounds are compared with those of isosteric compounds and elements, and the trends are discussed.

Stability of the Gaseous Ammonium Chloride Molecule

The equilibrium vapor effusing from a Knudsen cell, in which solid ND4Cl was evaporated, was analyzed by a quadrupole mass spectrometer. In the temperature range considered (335°–485°K) the main vaporization process corresponds to the decomposition of the solid towards gaseous ND3 and DCl; the measured enthalpy change ΔH°407dec[ND4Cl(s)] = 42.6 ± 2.0 kcal mole−1 is very close to that measured for NH4Cl: ΔH°407dec[NH4Cl(s)] = 42.5 kcal mole−1. Apart from the main gaseous species, small proportions (5 × 10−5–2 × 10−3) of ND4Cl molecules were also observed. The ND4Cl molecule fragments (> 99%) under electron impact and yields the ND4+(m / e = 22) ion. From the observed ion intensity ratios, as well as their dependence on temperature, D0°(NH4Cl ⇋ NH3 + HCl) = 10.0 ± 3.0 kcal mole−1 was obtained confirming Clementis computed prediction < 14.0 kcal mole−1.

Theoretical interpretation of reactions occurring in photochlorination

The Arrhenius A and E factors of over 60 elementary reactions in photochlorination systems have recently been evaluated experimentally in this and other laboratories. In this article a uniform treatment of most of these reactions is given by activated complex theories. Two parameters are fit to the data from two activation energies. The other activation energies follow the expected trend for reactions of chlorine atoms with hydrocarbons, but the reactions of chlorine atoms with chlorinated hydrocarbons do not follow the expected trends. For reactions with activation energy, the theory accounts very well for the magnitudes and trends of the Arrhenius A factors. For reactions with no activation energy, the activated complex theory as used by Gorin accounts for the order of magnitude of the rate constants of the group as a whole, but it fails to account for several pronounced trends in the data and is judged to be of no predictive value. For certain limited types of chemical reactions and over restricted ran...

Hydrogen abstraction from chlorinated ethanes by chlorine atoms

The hydrogen abstraction from the chlorinated ethanes by chlorine atoms has been investigated in the gas phase between 323 and 423°K. Absolute values of the rate constants have been obtained using a competition method with chloroform or methyl chloride as competitor. The activation energies and the pre-exponential factors are discussed.

Elementary rate constants in atomic chlorination reactions. Part 3.—Bond dissociation energies and entropies of the activated state

The experimental determination of numerous elementary rate constants in photochlorination reactions had been presented in preceding papers. These permit one to calculate bond dissociation energies, entropics of free radicals and of activated states. Schumachers results on the photochlorination of ethylene and Howlett and Bartons experiments on the pyrolysis of chlorinated ethanes are re-interpreted. The entropy of activation for hydrogen-abstraction reactions is interpreted in terms of translational electronic, rotational and vibrational terms.

Thermal dimerization of 1,3-cyclohexadiene in the gas phase

The thermal dimerizations of 1,3-cyclohexadiene(Chd), 2 Chd→exo-dicyclohexadiene (D3)kD3(a) and 2 Chd→endo-dicyclohexadiene (D4)kD4(b) have been studied between 471.1 and 638.5 K at pressures ranging from 25 to 630 Torr. These reactions are second order and the rates are unaffected by the surface-to-volume ratio or by the presence of added propene. The rate constants are given by log10kD3(1.mol–1s–1)=–(25 100 ± 500)/4.576 T+(5.97 ± 0.25), and log10kD4(1.mol–1s–1)=–(24 300 ± 500)/4.576 T+(6.08±0.25).

Mass-spectrometric studies of the vaporization of the sulphides of calcium, strontium and barium. The dissociation energy of S2 and SO

Abstract : CaS, SrS and BaS have been evaporated and the vapor analyzed by mass spectrometry.

Zur Thermodynamik von Selendampf: Massenspektrometrische Untersuchungen mit der elektrochemischen Knudsen-Zelle

Eine elektrochemische Knudsen-Zelle mit galvanischen Festkorperketten der Art Ag/AgJ /Ag2Se, wobei AgJ ein praktisch reiner Ionenleiter fur Silberionen ist, wird im Temperaturbereich von 200—450 C verwendet, um einen Selen-Dampfstrahl zu erzeugen, der dann im Massenspektrometer analysiert wird. Die Kombination dieser Techniken ergibt folgende Moglichkeiten: 1. Die Verdampfungsgeschwindigkeit des Selens kann coulometrisch bestimmt werden. Hierdurch ergibt sich eine Moglichkeit zur Druck-Eichung des Massenspektrometers. 2. Das chemische Potential des Selens ist bekannt und kann bei konstanter Temperatur in weiten Grenzen variiert werden. Es ist daher moglich, die verschiedenen Selenmolekule Sex getrennt zu untersuchen und ihr Verhalten bei Elektronenstos-Ionisation — speziell die Fragmentation — zu studieren. Mit Hilfe dieser Methode werden im Selendampf folgende Teilchen eindeutig identifiziert: Se2, Se3, Se4, Se5, Se6, Se7, Se8 und relative Ionisierungsquerschnitte, Partialdrucke und genaue thermodynamische Daten ermittelt.

Elementary rate constants in atomic chlorination reactions. Part 2.—Experiments in competitive systems

The gas-phase photochlorinations of mixtures of tetrachloroethylene with methane, methyl chloride, methylene chloride, chloroform and pentachloroethane have been studied in a static system. Reaction rates have been followed manometrically and photometrically. This technique permitted us to measure two elementary rate constants C2Cl4+Cl→C 2Cl5 (2); log k2=9.4, C2Cl 5H+Cl→C2Cl5+HCl(2′); log k′2=-723/T+9.8. Further experiments permitted us to measure the complex rate constant log (k′2k4/k 2k3)1/2=-1605/T+2.50, where k3 and k4 refer to the elementary reactions, C2Cl 5+Cl2→C2Cl6+Cl (k3) C2Cl5→C2Cl4+Cl.(k4) Using the results of the preceding paper and the calculated equilibrium constants for the chlorination of C2Cl4 and C 2Cl5H, all the eight elementary constants determining the rate of these photochlorinations have been calculated. Numerous cross-checks can further be performed and show complete agreement. Incidentally, the relative values of the rate constants for hydrogen abstraction from CH4, CH3Cl, CH2Cl2, CHCl3 measured previously by Knox have been checked.

Oxygen effect in the photochlorination of ethane

The inhibitory effect of oxygen on the photochlorination of ethane has been studied between 253 and 423°K. It can be explained by the removal of ethyl radicals by molecular oxygen: C2H5+O2→ C2H5O2 k9. The value k9 = 0.63 × 109 mole-1 l. sec-1 is in good agreement with literature data. The dependence of the rate on concentrations and light intensity is discussed and permits one to discard an alternative explanation involving the reaction Cl+O2→ClO2.