J. L. Franklin

Correlation of Excess Energies of Electron‐Impact Dissociations with the Translational Energies of the Products

Translational energies of products of unimolecular dissociations resulting from electron impact have been measured at the appearance potentials of the fragment ions. Excess energies for each process were determined from the measured appearance potentials and the known heats of formation of ground‐state products and reactants. Results are compared with the predictions of the statistical theory and found to be in agreement if the classical density of states is used. Application of the method to accurate determinations of heats of formation of radicals and radical ions is demonstrated.

Partitioning of excess energy in dissociative resonance capture processes

The translational energies of selected negative ions formed by dissociative resonance capture processes from the polyatomic systems NF3, BF3, CF4, C2F6, C3F8, and c‐C4F8 have been measured as functions of excess energy over the resonances. The excess energy in the molecular negative ion intermediate prior to dissociation has been calculated and partitioned into translational, vibrational, and, in some cases, electronic excitation of the dissociation products. The degree of vibrational activation in the intermediate state before dissociation is found to depend on the particular molecule under investigation and to vary from one dissociation channel to another. These observations are discussed in relation to theoretical concepts of dissociative resonance capture and given a qualitative explanation. The measurement of translational energy has led to a more complete interpretation of the states involved in the various processes and in computing ground state thermochemical properties of the decomposition products.

Proton affinities of neutral molecules

Abstract Values for proton affinities (gas-phase basicities) published during the past ca. 25 years are given. Methods for determining these values are discussed.

Heats of Formation of H3O+, H3S+, and NH4+ by Electron Impact

Electron impact fragmentations of some simple organic molecules have been investigated, making use of excess energy measurements. The results give values for the heats of formation to be 143, 191, and 148 kcal/mole for H3O+, H3S+, and NH4+, respectively. These values are consistent with limitations imposed by ion–molecule reactions and with crystal‐lattice calculations.

Excess energies in mass spectra of some oxygen-containing organic compounds

Excess energies of the electron-impact induced dissociation of several oxygen-containing compounds have been estimated by measuring the translational energies of the fragment ions. The heats of formation of CH3O, C2H5O, CH3CO, HCO, COOH, and their positive ions have been determined. The formyl radical has a heat of formation of 8 ± 3 kcal/mole. Ions of composition CH3O+ and C2H5O+ from these compounds always have the hydroxy carbinyl structure at threshold energies. The method is shown to be competitive with the best methods of chemical kinetics for determining bond dissociation energies.

Electron Affinities of the Halogen Molecules by Dissociative Electron Attachment

The electron affinities of the halogen molecules have been determined mass spectrometrically. This was accomplished by measuring both the appearance potentials and average translational energy of the negative halogen molecular ion resulting from dissociative electron attachment reactions. The values reported in this work agree favorably with those found in the recent literature. Also reported are the heats of formation of several free radicals used as auxiliary data.

Erratum: Use of translational energy measurements in the evaluation of the energetics for dissociative attachment processes

The translational energies of negative ions formed by dissociative resonance capture processes from CO, NO, CO2, and SO2 have been measured as functions of excess energy. The sums of the translational energies of O− and the corresponding neutral from CO and NO were found to be equal to the electron energy above onset over a range of about 1 eV. At higher energies, the translational energies dropped down from the expected values because of loss of the more energetic ions to the walls. With CO2 and SO2 the total translational energy was always E*/N, where E* is excess energy and N the number of vibrational modes, 3 in each case. The measurement of translational energy has also helped in interpreting the states involved in the various processes and in computing the ground state thermochemical properties of the decomposition products.

Correlation of Excess Energies of Dissociative Electron Attachment Processes with the Translational Energies of Their Products

Appearance potentials and translational energies of the products resulting from several dissociative electron capture processes have been measured. Excess energies were determined for each process from the measured appearance potentials and known ground‐state heats of formation of the products and reactants. As with positive ions, the results were found to agree with the predictions of classical statistical theory. Application of the method is demonstrated in determination of the electron affinity of radicals.

High‐Pressure Ion–Molecule Reactions in Carbon Monoxide and Carbon Monoxide–Methane Mixtures

In carbon monoxide at pressures above 0.2 torr, the principal product ion is C2O2+ formed by a three‐body process. The rate constant for the reaction is 1.43 × 10−28 cm6 molecule−2·sec−1. Above about 0.8 torr, the reaction appears to approach equilibrium with an equilibrium constant of 1482 referred to 1 atm as standard. At pressures of methane above 0.2 torr and small additions of CO, the only reaction observed in the protonation of CO by CH5+ with a rate constant of 5.54 × 10−10 cm3 molecule−1·sec−1. All other reactions are endothermic and are not observed. At pressures of carbon monoxide above 0.2 torr, the addition of small amounts of methane results in an H‐atom transfer reaction to CO+ with a rate constant of 13.7 × 10−10 cm3 molecule−1·sec−1. In addition, C2O2+ reacts to form HCO+, C2H3O+, and C3H3O+ with rate constants of 9.44, 4.37, and 0.76 × 10−10 cm3 molecule−1·sec−1, respectively.

High temperature negative ions: Electron impact of As4 vapor

Appearance potentials and ion translational energies have been measured for the negative ions As−, As2−, and As3− formed by dissociative resonance capture of As4. The following thermochemical values (all in kilocalorie/mole) have been obtained: Δ Hf,298o(As2−)=43.1± 4.5; Δ Hf,298o(As3−)=38.3± 4.3; E.A.(As2)=2.4± 4.1; E.A.(As3)=19.3± 8.2 and Δ Hf,298o(As3)=57.6± 3.9. The measurement of the increase in translational energy through resonance gave α = 0.43 for the three processes studied.