H. C. Straub

Absolute partial cross sections for electron-impact ionization of CH4 from threshold to 1000 eV

Absolute partial cross sections for the production of CH4+, CH3+, CH2+ , CH+, C+, H2+, and H+ from electron-impact ionization of CH4 are reported for electron energies from threshold to 1000 eV. The product ions are mass analyzed using a time-of-flight mass spectrometer and detected with a position-sensitive detector whose output demonstrates that all product ions are completely collected. The overall uncertainty in the absolute cross section values is ±3.5% for singly charged parent ions and is slightly greater for fragment ions. Although previous measurements are generally found to agree well with the present results for CH4+ and CH3+, almost all previous work for the remaining fragment ions lies lower than the present results and in the case of H+ is lower by approximately a factor of 4.

Absolute partial cross sections for electron-impact ionization of H2O and D2O from threshold to 1000 eV

Absolute partial cross sections for electron-impact ionization of H2O and D2O are reported for electron energies from threshold to 1000 eV. Data are presented for the production of H2O++OH++O+, O2+, H2+, and H+ from H2O and for the production of D2O+, OD+, O+, O2+, D2+, and D+ from D2O. The product ions are mass analyzed using a time-of-flight mass spectrometer and detected with a position-sensitive detector whose output demonstrates that all product ions are completely collected. The overall uncertainty in the absolute cross section values is ±4.5% for singly charged parent ions and is slightly greater for fragment ions. The cross sections for H2O and D2O are found to be the same to within experimental uncertainties except for the H2+ cross section which is approximately a factor of 2 greater than the D2+ cross section. Previous results are compared to the present measurements.

Absolute detection efficiency of a microchannel plate detector for kilo-electron volt energy ions

Measurements of the absolute detection efficiency of a commercial microchannel plate detector for kilo-electron volt energy ions are presented. The detector comprises two microchannel plates mounted in front of a resistive anode. It is found that when the detector is appropriately biased, and the ion impact energy is sufficiently high, ions with masses up to 131 amu are detected with equal efficiency and that this efficiency may remain constant over a period of years.

Absolute partial cross sections for electron‐impact ionization of CO2 from threshold to 1000 eV

Absolute partial cross sections for the production of CO+2, CO+, CO2+2, O+, C+, O2+, and C2+ from electron‐impact ionization of CO2 are reported for electron energies from threshold to 1000 eV. The product ions are mass analyzed using a time‐of‐flight mass spectrometer and detected with a position‐sensitive detector whose output provides clear evidence that all product ions are completely collected. The overall uncertainty in the absolute cross section values is ±3.5% for singly charged parent ions and is slightly greater for fragment and doubly charged ions. For the fragment ion cross sections, all but one of the previous measurements are observed to be significantly lower than the present results.

Absolute partial cross sections for electron-impact ionization of NO and NO2 from threshold to 1000 eV

Absolute partial cross sections for electron-impact ionization of nitric oxide and nitrogen dioxide are reported for electron energies from threshold to 1000 eV. The product ions are mass analyzed using a time-of-flight mass spectrometer and detected with a position-sensitive detector whose output demonstrates that all product ions are collected irrespective of their initial kinetic energy. Data are presented for the production of NO+, N+, O+, and NO2+ ions from NO; and for the production of NO2+, NO+, N+, O+, and (N2++O2+) ions from NO2. The overall uncertainty in the absolute cross section values is ±5% for singly charged parent ions, while that for the fragment ions may be as large as ±20%. For NO, the previously published data are generally in reasonable agreement with those presented here, although there remain some significant discrepancies with even the most recent work. No previous comprehensive study of NO2 has apparently been reported but the experimental NO2+ cross section data that are availab...

Use of capacitance diaphragm gauges at pressures down to 10−6 Torr

The useful range of a capacitance diaphragm gauge is extended down to 1×10−6 Torr with an uncertainty of ±10−7 Torr using computer‐based averaging. Gauge linearity is measured by observing the deflection of the diaphragm by the force of gravity. Precise pressure increments are generated by tilting the gauge through a range of accurately measured angles. By this procedure the gauge is observed to be linear to within ±1% plus 10−7 Torr between 1×10−6 and 8×10−3 Torr. Additionally, the deflection of the center of the diaphragm per unit pressure is found to be 2×10−5 m Torr−1.