Ionization and temperature dependent attachment cross section measurements in C/sub 3/F/sub 8/ and C/sub 2/H/sub 3/Cl

Journal Article · Wed Mar 01 04:00:00 EST 1989 · J. Chem. Phys.; (United States)

OSTI ID:6532462

Chantry, P J; Chen, C L

Total ionization and attachment cross sections have been measured in C/sub 3/F/sub 8/ at 330 K using an electron beam and a total ion collection technique, calibrated by similar measurements on N/sub 2/O and Xe. Our total ionization cross section is similar in general shape to a previous measurement of this type, but with typically half the magnitude. The ionization threshold cannot be accurately derived from these measurements, due to severe upward curvature immediately above threshold. The positive-ion signal rises above the background at 13.0 +- 0.1 eV, to be regarded as a lower limit to the true threshold. An overall ionization cross section with a threshold at 13.3 eV is recommended, based on threshold data from photoelectron spectroscopy and the present data between 14 and 80 eV. The room temperature total attachment cross section peaks at 2.8 eV with a value of 1.75 x 10/sup -17/ cm/sup 2/. This is 14 times smaller than the only other measurement of this type we are aware of. There is much better agreement with two more recently reported values unfolded from swarm experiments. The temperature dependence of the predominant dissociative attachment process, involving F/sup -/ production, was studied in a different apparatus using a mass filter and ion pulse counting. At 730 K the peak cross section has increased by approx.60% and the threshold is lower by 1.1 eV. This second type of measurement was used to study the predominant dissociative attachment process in C/sub 2/H/sub 3/Cl, involving Cl/sup -/ production. At 290 K this has a threshold at 0.85 eV and a peak at 1.35 eV of 3.2 x 10/sup -17/ cm/sup 2/, in good agreement with recent work elsewhere. At 850 K the cross section at the peak is 2.6 larger, and lower in energy by 0.33 eV, while at 0 eV it has reached 6 x 10/sup -18/ cm/sup 2/. At higher temperatures effects ascribed to thermal dissociation of the C/sub 2/H/sub 3/Cl were observed.

• Research Organization: Westinghouse RandD Center, 1310 Beulah Road, Pittsburgh, Pennsylvania 15235
• OSTI ID: 6532462
• Journal Information: J. Chem. Phys.; (United States), Journal Name: J. Chem. Phys.; (United States) Vol. 90:5; ISSN JCPSA
• Country of Publication: United States
• Language: English

Related Subjects

640304* -- Atomic
Molecular & Chemical Physics-- Collision Phenomena
74 ATOMIC AND MOLECULAR PHYSICS
ADDITIVES
BEAMS
CHLORINATED ALIPHATIC HYDROCARBONS
CROSS SECTIONS
DESIGN
DISSOCIATION
ELECTRICAL EQUIPMENT
ELECTRON ATTACHMENT
ELECTRON BEAMS
EQUIPMENT
FLUORINATED ALIPHATIC HYDROCARBONS
HALOGENATED ALIPHATIC HYDROCARBONS
HIGH TEMPERATURE
IONIZATION
LEPTON BEAMS
MEDIUM TEMPERATURE
ORGANIC CHLORINE COMPOUNDS
ORGANIC COMPOUNDS
ORGANIC FLUORINE COMPOUNDS
ORGANIC HALOGEN COMPOUNDS
PARTICLE BEAMS
PLASMA SWITCHES
SWITCHES
TEMPERATURE DEPENDENCE
TOTAL CROSS SECTIONS