We have measured the angular and energy distribution of the absolute cross sections for ejection of electrons from water vapor by electrons incident at 50-2000 eV. The angular range was 15" to 150" and the range of secondary electron energies was from 2 eV to an energy equal to the primary energy minus the first ionization potential. Electron energies were analyzed with a parallel-plate electrostatic analyzer with a resolution of 1.1%. Generally good agreement is obtained with the data of Opal et al. [J. Chem. Phys. 55, 4100 (1971)l at 500 eV except at the extremes of their angular range. Our energy distributions are compared to various binary-encounter-model calculations.
The authors report absolute differential and integral cross section measurements for electron-impact excitation of the ÃB11 electronic state of water. This is an important channel for the production of the OH (X̃Π2) radical, as well as for understanding the origin of the atmospheric Meinel [Astrophys. J. 111, 555 (1950)] bands. The incident energy range of our measurements is 20–200eV, while the angular range of the differential cross section data is 3.5°–90°. This is the first time such data are reported in the literature and, where possible, comparison to existing theoretical work, and new scaled Born cross sections calculated as a part of the current study, is made. The scaled Born cross sections are in good agreement with the integral cross sections deduced from the experimental differential cross sections. In addition they report (experimental) generalized oscillator strength data at the incident energies of 100 and 200eV. These data are used to derive a value for the optical oscillator strength which is found to be in excellent agreement with that from an earlier dipole (e,e) experiment and an earlier photoabsorption experiment.
Absolute values of cross sections for electron ejection by protons of 15-150 keV energy have been measured as a function of the angle and energy of the electrons. The range of angles was 10" to 160" and the electron energy range was 1-300 eV. The doubly differential cross sections were also integrated over energy or angle to obtain singly differential and total cross sections and also average ejected electron energies. Good agreement is obtained with Senger's DDCS-MT (doubly differential cross section-mixed treatment) theoretical treatment using the Salin factor.
Formation
of crystals in saturated and undersaturated solutions
is studied as a result of intense sound, or shock waves, produced
by high intensity focused laser pulses. Many tiny crystals are created
immediately throughout the solution by the laser-generated sound waves.
The compression waves can be created by focusing within the liquid
or onto the walls of a container. This new method allows for the instantaneous
formation of many “seed” crystals, which are then available
for further impurity-free crystal growth. More importantly, the tiny
“baby” crystals can be harvested before complete growth
into “adult” crystals can occur. This method is shown
to produce enough “baby” crystals to provide a glimpse
into the initial stages of crystal growth using modern microscopy
techniques such as SEM. By employing this new method, simple salts
such as sodium bromate, sodium chloride, sodium chlorate, and tartaric
acid were successfully crystallized. This method of crystal growth
may also allow for the generation of crystals which have previously
not been realized or are otherwise difficult to produce.
A pulsed crossed beam technique previously developed in this laboratory has been used to study the eledron impact ionization of copper. Previous measurements haw been very limited in scope and exhibit large discrepancies. Relative cross sections U" for the formation of I to 5 times ionized copper have been measured with high amuracy within the range 7.8-21OOeV. Individual cross sections have been obtained by normalization lo absolute values of uz obtained by Freund er a/ at energies below 200 eV using a fast crossed beam technique. Weak structures in a, can be attributed to Auger decay processes following the creation of 3s subshell and L shell vacancies but there is a lack of other pronounced structures in an for n > I where many close-lying subshell vacancies are involved. At 2100 eV cross sections us are less than three orders of magnitude smaller than U,,
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