W. E. Wentworth

A comparison of experimental determinations of electron affinities of pi charge transfer complex acceptors

The absolute electron affinities of pi charge transfer complex acceptors have been examined and the ’’best’’ values have been chosen. All of the results obtained by the magnetron method, including the estimates for hexafluorobenzene and tetracyanoethylene, were accepted. However, the magnetron results for anthraquinone and benzoquinone are not in agreement with charge transfer complex and half‐wave reduction potential data. The half‐wave reduction potential data and the charge transfer complex data for all of the other acceptors for which absolute electron affinities are available were found to be consistent with the usual correlation equations and their associated assumptions. The parameters from these correlations have been used to calculate the absolute electron affinities for about 150 acceptors.

Dissociative Thermal Electron Attachment to Some Aliphatic Chloro, Bromo, Iodo Compounds

Thermal electron attachment to several aliphatic fluoro, chloro, and bromo derivatives have been investigated in the range 30°–220°C and activation energies of 0–12 kcal have been determined. The relationship between the energy of activation (E*) and change in internal energy (ΔE) for the dissociative electron attachment reaction is uniquely linear with approximately a unit slope. Both chloro and bromo compounds apparently satisfy the same relationship. This empirical relationship can be used to predict bond dissociation energies for aliphatic chloro, bromo, and iodo compounds from the energy of activation for thermal electron attachment. Bond dissociation energies for 1,3‐dichloropropane, 1,2‐dibromoethane, and 1,3‐dibromopropane have been so determined as 75.6, 69.8, 70.9 kcal/mole, respectively. An expression for a two‐dimensional representation of the potential‐energy curve for the negative ion is proposed with which the linear relationship between E* and ΔE can be derived. The proposed potential‐ener...

Simple thermal decomposition reactions for storage of solar thermal energy

Abstract Simple thermal decomposition reactions have been investigated for the purpose of solar thermal energy storage. Ten criteria regarding the thermodynamics and kinetics of the reaction and the physical properties of the components of the reaction have been established. One particular reaction, the decomposition of ammonium hydrogen sulfate, has been evaluated in a preliminary manner and appears to satisfy all of the established criteria. The efficiency of storage is high and the decomposition occurs in the vicinity of 500°C. Other compounds such as ammonium halides, alkali and alkaline earth metal hydroxides, carbonates, sulfates and oxides have also been examined.

Chemical heat pumps—A basic thermodynamic analysis

Abstract The concept of a thermochemically driven chemical heat pump/refrigerator is discussed. Using Carnot analysis, it is shown that these systems can work closely to the maximal second-law efficiency. Criteria to be used in selection of chemical reactions for maximal efficiency are formulated.

The negative ion states of sulfur hexafluoride

Summary talk at the Lepton-Photon Symposium, Cornell University, Aug. 10-15, 1993.The reaction of SF6 with thermal electrons has been studied in a Ni‐63 atmospheric pressure ionization source for a quadrupole mass spectrometer (API/MS). The major ions that are observed are the parent negative ion (SF−6) and the parent minus a fluorine atom (SF−5). The ratio of [SF−5]/[SF−6] is highly temperature dependent above 500 K. The dissociation energy of the ground state negative ion into SF−5 and F has been determined to be 1.35±0.1 eV. This gives values of 3.8±0.15 eV for the electron affinity of SF5 and 1.15±0.15 eV for the electron affinity of SF6. The negative ion states of sulfur hexafluoride have been described by ‘‘pseudo‐two‐dimensional’’ Morse potentials calculated using experimental data.

Dependence of polyatomic ion mobilities on ionic size

The ion mobilities of 11 negative ions in nitrogen have been measured using a plasma chromatograph. The ions range from small negative ions such as NO2− to large organic ions such as the parent negative ion of 1‐naphthaldehyde, (C11H8O)−. The reduced ion mobilities for these negative ions, in addition to previously published ion mobilities of protonated hydrocarbons, were compared with the Langevin theory of ion mobility. The hard sphere average collision cross section between the ion and the neutral carrier gas N2 was estimated using two models: (1) static model where the ion is nonrotating and (2) rotational model where the ion is assumed to be rotating rapidly. Comparison of the calculated reduced ion mobilities with the experimental values reveals that the experimental collision cross sections are intermediate between those calculated using these two models. The experimental and calculated ion mobilities gave the best agreement using the mean collision cross section for the static and rotational model...

Correlation of Electron Beam and Thermal Electron Attachment Studies for Some Chloro, Bromo, Iodo Aromatic Compounds

The relationship between thermal electron attachment and electron beam studies for chlorobenzene, 0‐dichlorobenzene, 0‐chlorotoluene, 3′‐ and 4′‐chloroacetophenone, 1‐chloronaphthalene, bromobenzene, 0‐bromotoluene, 1‐bromonaphthalene, and iodobenzene is shown. The empirical negative‐ion potential‐energy function used to describe electron attachment to aliphatic halides is used for convenience in showing this relationship. Use of the two‐dimensional potential‐energy function permits a more quantitative representation of the mechanisms previously proposed. In some cases, the mechanisms have been altered from the earlier qualitative interpretation. In general the two types of measurement appear to be essentially in complete agreement. The agreement between the results further supports the empirical potential‐energy function for the negative ion. Also, thermal electron attachment to additional aromatic halogen derivatives was investigated by the pulse sampling technique as a function of temperature to furthe...

Pulsed discharge helium ionization detector universal detector for inorganic and organic compounds at the low picogram level

Abstract The pulsed discharge helium ionization detector is a universal ionizalion detector with sensitivity in the low picogram range. The response is approximately constant for saturated hydrocarbons on a per gram basis. Unsaturated and aromatic hydrocarbons have lower sensitivities, by about 10–20%. Heterocyclic substituents such as oxygen, chlorine and bromine tend to lower the response on a per gram basis. The dependence of the response on various parameters such as pulse interval and power, voltage, flow-rate and detector volume has been investigated. The response is linearly related to concentration over five orders of magnitude. The detector volume can be made small enough for high-speed microbore chromatography.

Thermal Electron Attachment to Nitrous Oxide

Thermal electron attachment to nitrous oxide was investigated in the range −66 to 215°C. The attachment was found to be dissociative in nature with an activation energy of 10.4±0.4 kcal/mole. The activation energy is thought to arise from electron attachment to molecules thermally excited primarily in the bending mode. In an attempt to explain the activation energy a simple Morse function was employed. Potential energy as a function of internuclear distance for both N2O and N2O− was generated at different N2O bond angles. In this manner a three‐dimensional surface for the reaction, N2O (linear)→N2O (bent)→ lim +e−N2+O−, was obtained. The potential surface has a minimum at a bond angle ∼160°. The electron affinity of N2O is estimated at 6.2±4 kcal from the calculated N2O− potential‐energy surface. This is in general agreement with other reported values.

Windowless pulsed-discharge photoionization detector application to qualitative analysis of volatile organic compounds

Abstract The effluent from a gas chromatograph was split and directed to four identical windowless photoionization detectors. These detectors use pure helium, helium with Ar (0.64%), Ar (4.15%) and Kr (0.58%) as the discharge gas. The relative ionization cross-sections can be obtained from the ratio of the normalized response using an internal standard. This value is characteristic of the compound and could be used for qualitative analysis. These ratios for 47 compounds encompassing 13 functional groups have been determined and are reported. The values have an average relative standard deviation of 2% for the majority of the compounds. The long-term reproducibility of a smaller set of compounds has been determined and was 0.78–2% relative standard deviation for the Ar detector and 5.6–11.3% (worse cases) where the response of the krypton detector is low.