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Carbon K-shell excitation in small molecules by high-resolution electron impact

The excitation of 1s carbon electrons has been observed in CO, CH4, CF4, CO2, COS, C2H2 and C2H4 by means of the electron energy-loss technique with high resolution (70 meV in the 300 eV excitation energy range) and at an incident electron energy of 1.5 keV. The energies, widths and vibrational structures of excited states corresponding to the promotion of 1s carbon electrons to unoccupied valence and Rydberg orbitals have been obtained. The validity of the equivalent-core model, and the role of resonances caused by potential barriers, are discussed.

A new technique for threshold excitation spectroscopy

A new technique has been developed for obtaining high resolution threshold excitation spectra in electron-atom and electron-molecule collisions. A very weak field penetrating into the target chamber produces a saddle point in the potential distribution which has the effect of focusing and enhancing the extraction efficiency of very low energy inelastically scattered electrons. Also the electron energy analyser is used in a special mode which sharpens the pass band for low energy electrons. Examples of threshold excitation spectra of He, Ar and N2 are given, and the onsets of the 23S and 21S states of helium have been used to determine accurately the energy (19.361+or-0.009 eV) of the 22S resonance in helium.

The observation of electric-dipole-forbidden inner-shell transitions in N2 and Ar by the electron energy-loss technique

By using low-energy electron impact excitation the authors have observed the first example of an inner-shell single-to-triplet transition, namely the transition from the ground state to the (1s)-1( pi 2p) 3 Pi state of N2. The parameters omega e and Re of the triplet state have been deduced from the observed vibrational structure of the transition. The parity-forbidden transition to the (2p32/)-14p state of Ar has also been studied, and the intensity of this transition relative to that of the electric-dipole-allowed transition to the (2p32/)-14s state has been measured as a function of the incident electron energy.

Nitrogen K-shell excitation in N2, NO and N2O by high-resolution electron energy-loss spectroscopy

The excitation of nitrogen 1s electrons has been observed in N2, NO, and N2O by using the electron energy-loss technique at an incident energy of 1.5 keV, and with an energy resolution of 0.075 eV. The energies, widths and vibrational structures of the inner-shell excited states have been obtained. The spectroscopic constants (internuclear separation Re, vibrational constants omega and omega x and quantum defect delta ) of the inner-shell excited states of N2 have been derived and have been found to be similar to those of the equivalent core states. The energies and vibrational structures of the inner-shell excited states of NO and N2O have also been interpreted in terms of the equivalent core model.

The charge-density method of solving electrostatic problems with and without the inclusion of space-charge

Discusses the singularities and approximations that occur in the charge-density method of solving electrostatic problems in which space-charge is absent (Laplaces equation) or present (Poissons equation). Describes the application of the method to electrostatic lenses in general and to the particular case of a high-current triode gun.

Electrostatic cylinder lenses. I. Two element lenses

A new method is presented of solving Laplaces equation for equidiameter coaxial cylinders separated by a finite distance. The results are used to obtain the focal lengths, focal points and spherical aberration coefficients of double cylinder electrostatic lenses over a large range of voltage ratios and cylinder separations.

Electron impact excitation of inner-shell excited states of CO

The design of an electron impact spectrometer for use in inner-shell studies of atoms and molecules is described. The use of the spectrometer to investigate inner-shell excited states of CO is reported. These states include the lowest lying valence states, (1s sigma C)-1(2p pi )1 Pi and 3 Pi , Rydberg states below the 1sC ionisation potential and doubly excited states above the ionisation potential.

Studies of the threshold electron impact ionization of helium

Studies have been made of the two outgoing electrons in ionization events for which the energy difference E between the total energy and the ionization energy is in the range from 0.2 to 3.0 eV. A coincidence time-of-flight technique has been used to measure their energy distribution and angular correlation functions, and a non-coincidence technique has been used to measure the partial cross section for the production of very slow electrons. The energy distribution function has been found to be uniform in the range of E from 0.2 to 0.8 eV and the width of the angular correlation function has been found to increase with the energy E in a way which is consistent with a E1/4 dependence. The yield of very low energy electrons is consistent, in the range of E from 0.2 to 1.7 eV, with a total ionization cross section having the energy dependence En, where n=1.131+or-0.019. These results are all consistent with the Wannier-Peterkop-Rau theory.

Angular distributions for resonant scattering of electrons by molecules

A general expression has been obtained for the angular distributions of electrons scattered resonantly by molecules. Specific expressions are given for particular types of molecules, and angular distribution coefficients are tabulated for these types.

Production and optical properties of an unscreened but localized magnetic field

A technique is described of using current carrying coils to produce a magnetic field that is well localized, falling off quickly with distance. The basis of the technique is that the first four magnetic multipole moments of the system are arranged to be zero. The deflection and electron optical properties of this type of field are then investigated. It is shown that a beam that initially converges to a point on the axis of symmetry of the field will be deflected in such a way that it still passes through the axis. Similarly, a beam originating at the axis will be asymptotically radial but with a changed direction.