Transfer cross sections for excitation

Figure 29. Ratio of cross section for excitation transfer followed by atomic autoionization (AAI), to total ionization cross section, as function of collision energy for systems He -Ar,Kr,Xe.77...

Total Cross Section for Excitation Transfer tialsof Fig. 17 and Table IV. 

The relative cross sections for excitation transfer have also been measured by Krenos (3). 

The total collision cross sections for excitation transfer, - ipa/a) and... 

Cross Sections for Excitation Transfer in Collisions between Alkali Atoms of the Same Species... 

It is obvious from Table 4.6 that the problem of excitation transfer from mercury to thallium is in a very unsatisfactory state. There is an apparent lack of consistency in the results of Kraulinya et al. (104), whose cross sections for excitation transfer to the 8 2S1/2, 6 2D2/2, and 7 2S1/2 levels in thallium seem to depend on the wavelength of the observed fluorescent component. The results of the two groups (Hudson and Curnutte and Kraulinya et al.) do not agree well with each other, and there is no consistent dependence of the measured cross sections on temperature. Finally, one would expect that the cross sections should decrease in some manner with increasing energy gap AE, but the results seem to indicate the opposite. It is manifest that considerable additional experimental work is needed to overcome these difficulties. 

On the other hand, the results of more recent studies by Cheron [111] and by Czajkowski and Krause [101] who investigated Hg(6 aP ) -> Cd(5 aP excitation transfer and obtained a cross section of 4.6 x 10 A, suggest that the transfer proceeds by ordinary 2-body collisions. Czajkowski s cross section, which is considerably smaller than Morozov s and Kraulinya s values, lies well on the general resonance curve shown in Fig. 4.9, together with other similar cross sections for excitation transfer between dissimilar partners. 

TABLE 1. Cross sections for excitation transfer (cxc.tr.), depolarization (depoL), and elastic process (elas.) in unit of nd jv. 

AE = 0 04 eV. Compare this with the mean kinetic energy of the atoms in a gas at 450 K and make an estimate of the cross-section for excitation transfer. 

The first (and still the foremost) quantum theory of stopping, attributed to Bethe [19,20], considers the observables energy and momentum transfers as fundamental in the interaction of fast charged particles with atomic electrons. Taking the simplest case of a heavy, fast, yet nonrelativistic incident projectile, the excitation cross-section is developed in the first Born approximation that is, the incident particle is represented as a plane wave and the scattered particle as a slightly perturbed wave. Representing the Coulombic interaction as a Fourier integral over momentum transfer, Bethe derives the differential Born cross-section for excitation to the nth quantum state of the atom as follows. 

The effects of reactant excitation On the cross sections for charge-transfer reactions have been briefly discussed in Section II.A.l.a. Bowers and... 

Neff estimated that up to 10% of charge transfer sodium atoms are produced in the excited state, which is consistent with the measurements of Ogurtsov et al. The experiment was not sensitive enough to measuring the corresponding emission cross sections for K+ -t- N2, where the optical transitions are at 770 and 766 nm, respectively. The cross section for exciting the K 5p( Pj) - transitions at 405 nm was found to be... 

Reactions of Complex Ions. For reactions of systems containing H2 or HD the failure to observe an E 1/2 dependence of reaction cross-section was probably the result of the failure to include all products of ion-molecule reaction in the calculation of the experimental cross-sections. For reactions of complex molecule ions where electron impact ionization probably produces a distribution of vibrationally excited states, kinetic energy transfer can readily open channels which yield products obscured by primary ionization processes. In such cases an E n dependence of cross-section may be determined frequently n = 1 has been found. 

---