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In exploring forces between charged particles and surfaces, we have sent a beam of low‐energy (0.5–40 eV) electrons through two (laser drilled) micron‐size pinholes in thin films of gold spaced 10 cm apart. Image forces associated with the solid around the second pinhole cause the beam to diverge into an angular distribution which is scanned with a movable slit and Channeltron detector. Distributions have widths which depend inversely on electron energy as expected from transit time considerations. The paraxial portion of the distribution appears to diverge as though from a weak negative electron lens. The impulse approximation for the radial component of the electron motion is used to derive a radial potential averaged along a line parallel to the pinhole axis. This potential approximately equals the expected value e/4x at x=10 A from the pinhole edge but deviates from this function at greater distances. This deviation may be due to geometric effects, to the impulse collision model employed, or to geometric irregularities at the edge. The results are useful in estimating efficiencies of filters for charged aerosol collection.

Our apparatus has been modified to permit measurements of absolute photoemission as well as reflectance of liquids in the vacuum UV. Photon fluxes are determined by filling the tandem ion chambers with argon. An electrometer is connected to the sample cup, which must be properly biased, to read electron currents leaving the cup. After argon ion drift into the cup is taken into account, the yields of photoelectrons per incident photon and per absorbed photon are obtained. These yield curves for liquid formamide (HCONH2) are similar to each other over the energy range studied (16–25 eV). They are nearly constant between 16 and 18 eV at 13.5% and decline toward higher energies. The surface and volume plasmon energies for formamide are near 19 and approximately 27 eV, respectively. We suggest that photoelectron excitation of surface plasmons may enhance the photoemission yield, while excitation of volume plasmons may reduce it. Values of electron mean free path derived from the yields and a simple three‐step ...

The reflectance of liquids squalane and squalene between 2 and 25 eV have been determined by closed cell double ionization chamber methods. Kramers–Kronig analysis of the data gives optical functions from which are calculated the dielectric functions, energy loss functions, and mean free path for photons and electrons. Values of yield predicted from a theoretical model of photoemission are found to be about 11% at 16 eV declining to 4% at 25 eV. However, no photoemission was observed over this energy range.

The reflectance of liquid hexamethylphosphoric triamide has been determined between 2 and 9 eV by the semicylinder method and between 10 and 25 eV by the double ionization chamber method. Kramers‐Kronig analysis of the data gave the optical and dielectric functions, the energy loss functions, and the effective number of electrons, all as a function of photon energy. Structure in the absorption spectrum and the imaginary part of the complex dielectric function at 7.5 and 11.5 eV are associated with excitation of π and σ electrons, respectively. The σ→σ* excitation is shifted in the energy loss function −Im(1/e) to 21 eV, indicating an appreciable degree of collective behavior. Of the total 68 valence electrons, the number of electrons taking part in optical processes and energy loss processes increases to 38 and 25, respectively, at 25 eV.

Monochromatic photons between 775 and 500 A were incident almost normally (15°) on the surface of liquid hexamethyl phosphoric triamide (HMPT). Incident and reflected beam strengths were measured with a double ion chamber filled with argon and the current leaving the cup of liquid was determined. After subtracting a portion of the current due to Ar+ drift into the cup, we obtained the photocurrent and, hence, the absolute photoemission yield. The yield falls from 9% at 16 eV to 5% at 25 eV. Such a falloff with increasing photon energy is expected from theory. The values are about double those calculated from theory using a three‐step model for the photoemission and using the Born approximation to calculate electron mean free paths. Conversely, if the experimental yields are used in the three‐step model, the electron mean free paths calculated from the data range from about 935 A at 16 eV to about 80 A at 24 eV and are about two to three times the theoretically predicted values.

Exact theoretical expressions for scattering of light incident at oblique angles on a cylinder are derived and compared with measurements on aluminized quartz fibers (diameters 0.9–2.2 μm) using a He-Ne laser. The free-electron gas model was used for the dielectric response function for Al. Fitting the angular positions of observed maxima and minima in the scattered intensity to the calculated values gave a sensitive method for determining fiber radii, reproducible within ± 3%–5%. These radii agreed with values from Fraunhofer diffraction at normal incidence within ± 10%–15%. The role of surface plasmon excitation in the scattering of light from cylinders is discussed briefly.

The far-field asymptotic solution for the diffraction of an electromagnetic plane wave by a cylinder-tipped half-plane is derived from the exact solution. It is demonstrated that the Fresnel diffraction plays an important role in the transition regions where the solution of the geometrical theory of diffraction fails. The asymptotic solution not only simplifies the numerical calculations but also gives a physical model of the exact solution.