The temperature dependence of cross sections for 62P1/2 ↔ 62P3/2 mixing in cesium, induced in collisions with CH4, CH3D, CH2D2, CHD3, and CD4 molecules, has been investigated in a series of sensitized fluorescence experiments over a temperature range 290–650 K. The various cross sections which are of the order of 10−15 cm2, and which exceed similar cross sections for cesium–noble gas collisions by 4 – 6 orders of magnitude, exhibit differences in their variation with temperature. This isotope effect in the collision cross sections is interpreted on the basis of a novel semiclassical theory of electronic to rotational energy transfer. The cross section for mixing induced by collisions with CF4, which was determined in a subsidiary experiment, and which is 2–3 times larger than the methane cross sections, does not show comparable behavior with temperature, probably because the energy transfer takes place to closely lying molecular vibrational states.

CD % 20! F= 16h CO o g 8 / EMISSION CROSS SECTION \ 'POLARIZATION 0.5 10 20 3[keV] i_L_ -0.60 § -0.40 g < i -J H -0.20 £ 50 100FIG. 3. Cross sections and negative polarizations plotted as a function of the ion-beam energy for the Ne I 6266-A radiation from the p 5 level for the Na + -Ne system. pendent oscillations present in the total excitation cross section for thep 5 level can be accounted for nearly exclusively by the mechanism responsible for the polarization. This is not the case for the oscillations present in the light emitted from the p 1 level, a 1 S 0 term not exhibiting polarization.The present data show that for systems such as 2 P U2 ) + CH 4 , where CH 4 is one of the deuterated isotopes of methane. Collisions with Rb(5/>) in place of Cs(6/>) have also been studied, as have collisions with other molecules. We restrict consideration here 741

The dependence on temperature of the cross sections for 2P1/2 ↔ 2P3/2 mixing in cesium, induced in collisions with various deuterated hydrogen, ethane and propane molecules, has been studied in the range 290–650 K. In the cases of hydrogen and ethane, the behavior of the cross sections was found to depend on the degree of deuteration of the molecules. The very large sizes of the mixing cross sections and the isotope effect observed in their variation with temperature, are ascribed to the phenomenon of electronic to rotational energy transfer.

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Subnanosecond photoconductive switching has been observed in ultraviolet illuminated type IIa diamonds. Switching efficiencies up to 50% were attainable in coaxially mounted samples for direct current bias voltage as high as 8 kV at room temperature.