Dennis L. McCorkle

Electron attachment to chlorofluoromethanes using the electron-swarm method

Electron attachment rate constants, as a function of pressure‐reduced electric field, were measured in mixtures with nitrogen for CCl3F, CCl2F2, and CClF3 using the electron swarm method. From these data total electron attachment cross sections σa(e) as a function of electron energy e were determined for the chlorofluoromethanes using the electron‐swarm unfolding technique and a new set of electron energy distribution functions for N2. For CCl3F and CCl2F2 three maxima in σa(e) were found at thermal energy, 0.25 and 0.75 eV and at 0.07, 0.30, and 0.93 eV, respectively. Only one pronounced maximum in σa(e) for CClF3 was observed at 1.4 eV. The thermal values of the attachment rate constant for CCl3F, CCl2F2, and CClF3 are, respectively, 3.90×108, 4.00×107, and 6.05×103 sec−1 Torr−1. Additionally, comparisons are made between the σa(e) calculated for these and other molecules using both the new electron energy distribution functions for N2 and those determined earlier. Substituent effects on the number and ...

Electron attachment to halocarbons of environmental interest: Chloroethanes

Electron attachment to the chlorofluoroethanes 1,1‐C2Cl2F4, 1,2‐C2Cl2F4, 1,1,1‐C2Cl3F3, and 1,1,2‐C2Cl3F3 was investigated in dilute mixtures with nitrogen and argon using the electron swarm method. The 1,1,1‐C2Cl3F3 molecule has a very large electron attachment rate constant at thermal energy (2.8×10−7 cm3 s−1); the rate constant for this molecule decreases monotonically with increasing electron energy above thermal. The other chlorofluoroethanes investigated attach electrons less strongly and show maxima in the rate constant vs mean electron energy at ∼0.5 eV. For all four compounds, the measured rate constants are due primarily to dissociative electron attachment producing Cl−. Electron attachment cross sections were determined for these halocarbons which showed the existence of several negative ion states below ∼2 eV. Additionally, the temperature dependence of electron attachment to 1,1‐C2Cl2H4 was investigated from 323–473 K. The measured rate constants and unfolded cross sections indicated electron...

Ramsauer-Townsend minima in the electron-scattering cross sections of polyatomic gases: methane, ethane, propane, butane, and neopentane

Electron drift velocities, w, as a function of temperature were measured and on the basis of these data, Ramsauer-Townsend (RT) minima were found in the cross section for momentum transfer, sigma m, for all these gases. The position of the RT minimum and the magnitude of the corresponding sigma m at the energy where the minimum occurs are 0.12, 0.14, 0.14, and 0.25 eV and 1.2, 3.0, 4.6, and 5.8*10-16 cm2 for ethane, propane, butane, and neopentane, respectively. The density dependence of the w for neopentane was also investigated. This latter investigation and similar ones in the literature on methane, ethane, and propane are discussed in connection with the observed RT minima and the mobility of thermal electrons in the low- and high-pressure vapours and the liquids of these compounds.

Electron attachment to Cl2

Abstract The electron attachment rate constant for Cl 2 as a function of the mean electron energy (0.04–0.78 eV) and temperature (213–323 K) has been measured and is reported; it shows a maximum at near thermal energy and is attributed to dissociative electron attachment via the ground state 2 Σ u + of Cl 2 − from the ground state 1 Σ g + of Cl 2 .

Dissociation of benzene and methylene chloride based on enhanced dissociative electron attachment to highly excited molecules

We present preliminary results on a low-pressure glow-discharge-based process for the destruction of dilute concentrations of volatile organic compounds. Methylene chloride and benzene were studied in dilute mixtures with Ar, Ne and He rare gases. The destruction efficiency was observed to increase with increasing pressure. This and other observations are compatible with molecular dissociation by dissociative electron attachment to high-lying Rydberg states of molecules produced via excitation transfer from the metastable states of the rare gases.

Electron Attachment to F2

The rate constant ka for electron attachment to F2 has been measured at ambient (298 K) temperature T in the buffer gas Ar over the mean electron energy 〈e〉 range 0.40–2.95 eV; similar measurements were made at T=233, 298, and 373 K in the buffer gas N2 over the 〈e〉 range 0.04–0.75 eV. The ka(〈e〉) function attains a maximum value of 1.7×10−8 cm3 s−1 (T=298 K) at ∼0.04 eV and decreases monotonically with increasing 〈e〉 above thermal energy; the magnitude of ka increases only slightly with increasing T. The ka(〈e〉) data at 298 K were unfolded and the resultant cross section σa(e) shows a main maximum at ∼0.0 eV, a shoulder at ∼0.5 eV, and a weak maximum at ∼1.1 eV. Possible electron attachment processes are discussed to account for the energy dependence of σa(e). Also discussed, in the light of the present measurements, are published experimental and theoretical results on ka(〈e〉) and σa(e).

Effect of temperature on the low-energy (≲1eV) electron attachment to perfluorocyclobutane (c-C4F8)

Abstract A large decrease in the total electron attachment rate constant K for c C 4 F 8 with increasing temperature T (300 to 560 K) has been observed for mean electron energies 〈ϵ〉 ≲ 0.8 eV, where the electron attachment is non-dissociative. Possible origins for the observed large negative effect of temperature on K a (〈ϵ〉) are discussed.

Mass identification of negative ions in excimer-laser-irradiated triethylamine: atomic rearrangements in electron attachment to highly excited states

Abstract Efficient negative-ion formation via electron attachment to triethylamine (TEA) laser-excited to energies above its ionization potential had been reported; however, the evidence for negative-ion formation was indirect, and the identities of the negative ions were not known. In this Letter, we describe an apparatus where the negative (and positive) ions produced in a gas cell via laser irradiation can be extracted to a time-of-flight mass spectrometer for mass identification and present the results obtained for excimer-laser-irradiated TEA. It is shown that extensive atomic rearrangements can occur in dissociative electron attachment to highly excited states of polyatomic molecules.

The ionization threshold of N,N,N’,N’‐tetramethyl‐p‐phenylenediamine in dense fluid ethane; effects of fluid density and temperature

The ionization threshold IF of N,N,N’,N’‐tetramethyl‐p‐phenylenediamine in ethane, has been measured in the density (ρ) range 0.15–13.30 M/l and over the temperature (T) range 295–413 K, using a multiphoton ionization conductivity technique. The IF was found to be a function of both ρ and T in the ranges studied. At a fixed T (=373 K), IF was found first to decrease with increasing ρ and then to level off at densities of ∼10 M/l. For ρ≥11 M/l and T=295 K, the IF was found to increase with increasing density. At constant density (ρ=5.90 M/l ) IF decreased with increasing T between 323 and 413 K. These results are analyzed and discussed in relation to the effect of ρ and T on the electron conduction band energy V0 and the medium polarization energy P+. The changes in the IF with ρ are attributed to the dependence of V0 and P+ on ρ, while the dependence of IF on T is attributed to the effects of T on V0 rather than on P+.

Drift velocities of excess electrons in 2,2,4,4-tetramethylpentane and tetramethylsilane: A fast drift technique

Abstract A new fast drift technique for the measurement of short drift times for excess electrons is dielectric liquids is described. The technique was used to measure the drift velocities of excess electrons in 2,2,4,4-tetramethylpentane and tetramethylsilane as a function of the applied uniform electric field E up to respectively 11.5 × 10 4 and 12.3 × 10 4 V cm −1 ; at these maximum values of E , the drift velocities are 2.6 × 10 6 and 7.4 × 10 6 cm s −1 , respectively.