Cornelius E. Klots

Thermochemical and kinetic information from metastable decompositions of ions

Formulations are examined for connecting average kinetic energies of the products of a unimolecular decomposition with the total available energy. A straightforward method for the calculation of kinetic shifts is then described. Existing data suggest, nevertheless, that the effective number of internal degrees‐of‐freedom for energy disposal may be greater than the physical number, a result inaccessible to existing theory. A formal reconciliation is indicated here.

Kinetic energy distributions from unimolecular decay: Predictions of the Langevin model

The kinetic energy released in a unimolecular decomposition is examined within the framework of quasiequilibrium theory. It is assumed that the motion is governed by the long‐range forces between the separating moieties. Explicit formulas are obtained for cases where the total angular momentum is either very low or very high. Comparison with experiment and with other formulations is made.

Electron attachment to van der Waals polymers of carbon dioxide and nitrous oxide

Negative ions formed by electron attachment to carbon dioxide and nitrous oxide, expanded through a sonic nozzle, are reported. In each case the dominant ions have the formula O−(M)n, where M is the parent monomer. The appearance potential of O− in each case indicates the absence of ’’hot bands.’’ Ions with the formula (CO2)−n, with n?2, evidently formed by evaporative electron attachment, seem to be stable with respect to autodetachment. The ’’three‐body’’ mechanism for attachment of thermal electrons to nitrous oxide and oxygen is discussed.

Production of negative ions from CH3X molecules (CH3NO2, CH3CN, CH3I, CH3Br) by electron impact and by collisions with atoms in excited Rydberg states

Thermal electron attachment to nitromethane, methylcyanide, methyliodide, and methylbromide is compared with capture of electrons by these molecules from highly excited Rydberg states of atoms. Data on thermal electron attachment to CH3NO2 are consistent with a three‐body attachment process, with the nature of the third body being important. The thermal energy electron attachment rate constant for CH3CN is ≤1.24×10−14 cm3 sec−1. Some results on dissociative electron attachment and ion pairing processes in CH3NO2, CH3CN, CH3I, and CH3Br are also presented.

Rate constants for unimolecular decomposition at threshold

Abstract The character of rate constants for a dissociation occurring near threshold on an attractive potential-energy surface is discussed. Application is made to the attachment of electrons to SF6 and CCl4, and to the autoionization of SF6-. Implications for isotope separation schemes based on the competition between the autoionization and dissociation of SF6- are noted.

Electron attachment to carbon dioxide clusters in a supersonic beam

Negative ions have been observed in a time‐of‐flight man spectrometer with charge‐to‐man satios corresponding to (CO2)−n with 2⩽n⩽6. It is concluded that these ions are formed by electron attachment to clusters formed in the rapidly expanding CO2 beam from a sonic nozzle. (AIP)

Quasiequilibrium rate constants for thermionic emission from small particles

Abstract A modified hard-sphere model for electron capture by small aggregates is used to derive an expression for the rate constants for thermionic emission from isolated aggregates of matter. Its connection with earlier models for autoionization is indicated. The use of generalized Arrhenius plots for comparing experiment and theory is outlined.

Kinetics of dissociation and thermionic emission in the C60 and C70 molecules

Abstract Kinetic energy release distributions are reported for the emission of C2 from the positive ions of C60 and C70. These are transformed into Arrhenius activation energies for dissociation of the neutral molecules. Microcanonical rate constants for dissociation the thermionic electron emission from these molecules are then presented. It is concluded that the latter process is parasitic to dissociation in each case.

Electron attachment to van der Waals polymers of water

Negative ions resulting from electron attachment to van der Waals polymers of water are reported. The most prominent ions observed consititute a homologous series with the stoichiometric formula OH−(H2O)m. They and the positive ions H+(H2O)m are ascribed to ion–molecule half‐reactions. The ionization of van der Waals complexes as a method for preparing ’’collision complexes’’ is discussed.

Thermal kinetics in small systems

Standard microcanonical rate‐constant theory can be cast in a form which closely resembles and, in the case of a sufficiently large medium, reduces to that of the canonical ensemble. This relation permits a new understanding of the role of an activation energy in a chemical reaction. A facile methodology is also proposed for the extraction of thermodynamic data from kinetic studies of small media.