Impact Franck

J. Franck (Gottingen) and G. Hertz (Halle) discovery of the laws governing the impact of an electron upon an atom. 

Table I. Distribution of Excited H2+ Produced by Franck-Condon Electron Impact Processes with 50-Volt Ionizing Electrons...

One expects the impact of the electronic matrix element, eqs 1 and 2, on electron-transfer reactions to be manifested in a variation in the reaction rate constant with (1) donor-acceptor separation (2) changes in spin multiplicity between reactants and products (3) differences in donor and acceptor orbital symmetry etc. However, simple electron-transfer reactions tend to be dominated by Franck-Condon factors over most of the normally accessible temperature range. Even for outer-... 

The combination of a mass analyzer with the electron impact apparatus enabled the scope of the pioneer work of Hertz, Lenard, Franck, and Lozier to be greatly extended, and results of less ambiguity were obtainable. Such experiments lead in general to a curve relating the ion current... 

Spiders are an important order of carnivorous arachnids having a great impact on many ecosystems. Because most of their prey consists of insects, they can play an important role in controlling pest insects in agricultural crops. There are currently about 36000 described species, out of an estimated overall number of 60000-80000 species (Platnick, 1999). Unlike the situation with insects (Francke and Schulz, 1999), pheromones and other semiochemicals of arachnids, and especially spiders, have received little attention from researchers. What information is available on the use of semiochemicals by spiders will be reviewed and discussed in this chapter. 

Franck-Condon distribution Electron-impact ionization high kinetic-energy ion beam... 

Hj+(A-2S+) Franck-Condon dislribution Electron impact-mass spectrometry... 

H2+(Jf2S,+ ) Franck-Condon distribution Merging ion-neutral beams electron-impact ionization... 

Utilizing ionization efficiency curves to determine relative populations of vibrationally excited states (as in the photoionization experiments) is a quite valid procedure in view of the long radiative lifetime that characterizes vibrational transitions within an electronic state (several milliseconds). However, use of any ionization efficiency curve (electron impact, photon impact, or photoelectron spectroscopic) to obtain relative populations of electronically excited states requires great care. A more direct experimental determination using a procedure such as the attenuation method is to be preferred. If the latter is not feasible, accurate knowledge of the lifetimes of the states is necessary for calculation of the fraction that has decayed within the time scale of the experiment. Accurate Franck -Condon factors for the transitions from these radiating states to the various lower vibronic states are also required for calculation of the modified distribution of internal states relevant to the experiment.991 102... 

As the speed of the impacting electrons is still further increased no new processes are observed by the positive ray or clean-up methods. Some experimenters have observed additional ionization setting in at about thirty volts. Of more importance, however, are the results of Franck and Blackett, who showed that the emission of Balmer lines was a primary result of impact of thirty volt or higher speed electrons. In other words, they showed dissociation may occur with excitation of one (or perhaps both) atoms. 

Consider the possible effect of an electron impact on an H2 molecule. If the electron has less than 11 volts the only possible transition it may cause is to the 13S state. But applying the Franck-Condon principle we see that the probability of such a transition will be small except for those nuclear separations where the 13S curve nearly coincides with that for the 23S term. In other words we might expect a little but only a little atomic hydrogen to be produced below eleven volts since the 13S state is unstable. 

The A 3 + state has a radiative lifetime of 2 s, and is therefore long-lived on the time scale of the molecular beam experiments, where it was produced by electron impact on a beam of N2 diluted with Ar, cooled to liquid nitrogen temperature. Calculations of the Franck-Condon factors show that direct excitation of the A state is expected to populate many vibrational levels, and a major feature of the magnetic resonance studies was that spectra involving the first thirteen vibrational levels (v = 0 to 12) were obtained. The accurate and extensive determination of the vibrational constants, given above, was therefore of considerable importance. 

Studies of electron-impact ionization of molecular nitrogen and oxygen near threshold [141, 142] have demonstrated that a Franck-Condon distribution of vibrational levels is not obtained because many ions are formed indirectly, via autoionizing states. The importance of autoionization can be seen in the case of where the Franck-Condon factors for transitions... 

The vibrational population in the excited state n(v ) is determined by the vibrational population in the ground state n(v), if the electron impact excitation from the ground state is the most dominant excitation mechanism. The application of the Franck-Condon principle for electron impact excitation allows a calculation of n(v ) from n(v) based on the Franck-Condon factors between ground and excited state. Figure 4.2 illustrates this scheme for the three states involved in the Fulcher transition upper and lower state, d3nu and a3A)] respectively, in the triplet system and the ground state... 

The potential curves displayed in Fig. 20.6 schematically show the possibilities for the production of highly energetic fragment ions. Depending on the internuclear distance of the neutral molecule that defines the Franck-Condon region and the electronic state that will be reached by the electron impact... 

The lower triplet state corresponds to the 3a (3a ) transition of the tt,x type. This band could underlie the 385-to 200-nm band since the Franck-Condon accessible region may be quite high in energy. Excited electronic states of ketene have been recently studied by electron impact spectroscopy (87). 

The electron impact results are vertical ionization potentials. These may exceed the spectroscopic adiabatic ionization potential by the vibrational energy excited in the ion because of the Franck-Condon principle. Here adiabatic is used in the sense of without... 

The selective data on Franck-Condon maxima for transitions from A o, recorded in Table 2, were obtained from electron impact (38) and T transient absorption studies (39). They... 

The Franck-Hertz experiment and atomic energy levels Electrons can excite atoms from one quantum state to another by energy transferred during collisions. The threshold energy for excitation exactly matches the emission of light as the atom drops back down to the lower state, thus confirming the existence of quantized states and showing that they may be excited by either mechanical impact of electrons or absorption of photons. 

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