Field ionization rates

Mass Spectra. Obtained by Gillis et al (Ref 104). Field ionization and electron impact ionization mass spectra are given by Brunee et al (Ref 54) Mechanical Properties < Sound Velocity. Hoge (Ref 77) obtained the following ultimate stress as a function of strain rate for machined discs (1.77g/cc) of PETN (all failures were brittle fractures)... 

While excitation processes in strong laser fields have not received as much attention as ionization rates and high-harmonic generation, the study of excitation is an important aspect of our overall understanding of the behavior of molecules in strong laser fields. 

Considering that J 2 I 2 and that the ionization rates at R = Rq have little 9 dependence [35], the dominant difference should be due to the electron and nuclear dynamics in the steps 2 and 3. The observed single molecule responses are obtained by superposing the radiation from all the molecules with random orientation coherently. For linearly polarized laser field, whose direction is defined as x axis, the observed dipole moment is given by... 

Example Secondary kinetic isotope effects on the a-cleavage of tertiary amine molecular ions occurred after deuterium labeling both adjacent to and remote from the bond cleaved (Chap. 6.2.5). They reduced the fragmentation rate relative to the nonlabeled chain by factors of 1.08-1.30 per D in case of metastable ion decompositions (Fig. 2.18), but the isotope effect vanished for ion source processes. [78] With the aid of field ionization kinetic measurements the reversal of these kinetic isotope effects for short-lived ions (lO -lO" s) could be demonstrated, i.e., then the deuterated species decomposed slightly faster than their nonlabeled isoto-pomers (Fig. 2.17). [66,76]... 

At still higher fields carriers can acquire enough energy from motion in an electric field to create electron—hole pairs by impact ionization. For silicon the electron ionization rate, which is the number of pairs generated per cm of electron travel, depends exponentially on electric field. It is about 2 x 103 cm-1 for a 50 kV/cm field at 300 K. The electric field causes electrons and holes so created to travel in opposite directions. They may create other electron—hole pairs causing positive feedback, which leads to avalanche breakdown at sufficiently high fields. 

Field ionization can also be enhanced by photons. Tsong et al.43 searched for this effect and found that Ar field ion current near the threshold field of field ionization from an aluminum oxide tip could be enhanced by a factor of about 5 when the tip was irradiated with 4.16 eV photons from laser pulses of 2 p,s width at a pulse repetition rate of 25 Hz, or a duty cycle of only 0.005%. As the photon energy is much too small to... 

Field ionization can also be treated as a direct electronic transition from the atomic state to a vacant state at the surface. Following the Fermi golden rule, the rate of field ionization is given by31... 

Fig. 2.12 Average charge state in field evaporation of Mo as a function of the applied field, obtained by Kellogg.68 The field evaporation rate is kept nearly constant by adjusting the temperature of the pulsed-laser heating. Curves are theoretical results A from the image-hump model, B from the same calculation with post field ionization correction. Calculations are based on those of...

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