O. J. Orient

Electron impact ionisation of H2O, CO, CO2 and CH4

Utilising a crossed electron-beam-molecular-beam collision geometry and the relative flow technique normalised values of total and partial ionisation cross sections for H2O, CO, CO2 and CH4 have been measured. The present total ionisation cross sections agree well with those reported previously by Rapp and co-workers (1965). However, data on the partial ionisation cross sections widely disagree with some previous results.

Miniature, high-resolution, quadrupole mass-spectrometer array

A miniature quadrupole mass spectrometer array consisting of 16 rods in a 4×4 array is reported. Each rod is 25 mm in length and 2 mm in diameter. The ionizer is of a miniature Nier-type design, and the detector is a channel-type electron multiplier. Operating frequencies are 5.3, 7.1, and 12.9 MHz. The mass range demonstrated herein is 1–300 u; and the resolution of the system is 0.1–0.5 u (full width at half-maximum), or m/Δm=600. The present sensitivity is calculated and measured to be approximately 1×1012 counts/Torr s.

Production of negative ions by dissociative electron attachment to SO2

Dissociative electron attachment cross section measurements for the production of O−, S−, and SO− have been performed utilizing a crossed target SO2 molecule beam–electron beam geometry. The relative flow technique is employed to determine the absolute values of cross sections. The attachment energies corresponding to various cross section maxima are: 4.30 and 7.1 eV for O−/SO2; 4.0, 7.5, and 8.9 eV for S−/SO2; and 4.7 and 7.5 eV for SO−/SO2.

A compact, high-resolution Paul ion trap mass spectrometer with electron-impact ionization

A Paul ion trap has been developed for use as a high-resolution mass spectrometer. It is of small size (r0=10 mm), having a resolution of m/Δm=324, which is limited by the machining accuracy of the trap. It has a demonstrated mass range of 1–300 u, and a sensitivity of 2×1014 counts/Torr s, or to 500 parts per trillion detection sensitivity in a typical vacuum of 10−5 Torr. Ionization of the room-temperature gas within the trap is carried out with an electron beam traversing the trapping volume. The trap operates in a radio frequency only mode, and no dc is required. Trapping is accomplished within the well depth of the dynamic radio frequency potential, and no cooling gas is required, such as helium. This combination of factors makes the trap potentially of use for autonomous operation in harsh environments requiring low power, low weight, and low volume, such as undersea, on the surface of a planet or asteroid, or in a spacecraft.

Mass spectrometric determination of partial and total electron impact ionization cross sections of SO2 from threshold up to 200 eV

A new approach to quadrupole mass spectrometric measurement and analysis has been used to study the electron impact ionization of SO2 to determine the cross sections for the production of O+, S+, SO+, and SO+2 from SO2. The relative flow technique is utilized to determine the cross section values. The threshold potentials are found to be 12.5 eV (SO+2), 16.5 eV (SO+), 16.5 eV (S+), and 23.5 eV (O+). The partial cross section values at 100 eV electron impact energy are 4.20×10−16 cm2 for SO+2, 1.65×10−16 cm2 for SO+, 0.90×10−16 cm2 for S+, and 0.25×10−16 cm2 for O+.

Observation of CH A→X, CN B→X, and NH A→X emissions in gas‐phase collisions of fast O(3P) atoms with hydrazines

Optical emissions in single‐collision reactions of fast (20 eV laboratory translational energy) O(3P) atoms with hydrazine, methylhydrazine, and 1,1‐dimethylhydrazine have been measured in a crossed‐beams geometry. The emissions were observed in the wavelength range 325–440 nm, and were identified as the CH (A 2Δ→X 2Πr) (for methylhydrazine), CN (B 2Σ+→X 2Σ+) (for methylhydrazine), and NH (A 3Π→X 3Σ−) transitions (for all three hydrazines). The experimental vibration‐rotation bands were fit to a synthetic spectrum of CH, CN, and NH with given vibrational and rotational temperatures.

Oxidation of silicon with a 5 eV O− beam

A silicon wafer has been oxidized at room temperature in vacuum using a pure, ground‐state beam of O− ions. The beam was of sufficiently low energy that no displacement damage or implantation was energetically possible. The resulting SiO2 films were analyzed with x‐ray photoelectron spectroscopy. A logarithmic dependence of oxide thickness on dose was observed, with an extrapolated oxidation efficiency of unity for the clean silicon surface. A distinct initial oxidation phase was observed, with an anomalously high level of silicon suboxides. In addition, the valence‐band offset between the silicon and the oxide was unusually small, suggesting a large interfacial dipole.

Elastic scattering of electrons from SO2

Using a crossed electron beam–molecular beam scattering geometry and the relative‐flow technique, ratios of elastic differential cross sections of SO2 to those of He have been measured at electron impact energies of 12, 20, 50, 100, 150, and 200 eV. At each energy, an angular range of 15° to 150° has been covered. These ratios have been multiplied by previously known He elastic differential cross sections to obtain elastic differential cross sections for SO2. From a knowledge of differential cross sections, integral and momentum transfer cross sections have been determined. Using the two‐potential theory of e‐molecule scattering, calculations were also performed and compared with the measurements.

Reversal ion source: A new source of negative ion beams

We demonstrate a new type of ion source for producing either pulsed or continuous negative ion beams. The source, dubbed the ‘‘reversal ion source,’’ utilizes an electrostatic ‘‘mirror’’ which reverses trajectories in an electron beam, producing electrons at their turning point having a distribution of velocities centered at zero velocity. A gas which attaches zero‐velocity electrons is introduced at this turning point. Negative ions are produced by the attachment or dissociative attachment process. The cross section for this process is extremely large, varying as (electron energy)−1/2, or just the s‐wave threshold law. The operation of the source is demonstrated for continuous and pulsed production of Cl− beams by dissociative attachment to CFCl3. Estimates of the current density of this source are given, and applications to the production of ions through higher energy resonances are discussed.

Optical emission generated by collisions of 5 eV O(3P) atoms with surface-adsorbed hydrazine

Optical emission has been observed corresponding to vibrational bands in the NH (A 3Π→X 3Σ−) electronic transition during collisions of 5 eV, ground‐state oxygen O(3P) atoms with MgF2 and Ni surfaces continuously exposed to a beam of hydrazine (N2H4). The NH emission intensity is observed to be about five times greater for MgF2 than for Ni. No dependence on temperature was observed for either surface in the range 240–340 K, implying that the NH‐producing intermediate species is tightly bound. The half‐lifetime for desorption of hydrazine from each surface was measured. This was found to be 120 min for the MgF2 surface at 240 K, and ≤20 min for Ni. After exposure the surface composition was measured using x‐ray photoelectron spectroscopy (XPS) on the exposed and unexposed areas of both targets.