Excitation cross sections for

It is seen that the individual de-excitation cross sections for a particular excited atom are governed by the individual interactions. The de-excitation cross sections of He(2 S, 2 S, and 2 P) are reasonably interpreted as follows. Two important factors are readily extracted from the semiempirical formula for the Penning ionization cross section, so that the rational relation of the Penning ionization cross section is obtained ... 

There are no experimental data of excitation cross sections for proton and alpha particle impact for water. The proton cross sections were obtained by scaling of the electron excitation cross sections for high-energy protons >500 keV [201]. For the lower-energy regions, the semiempirical model developed by Miller and Green [202] was adopted, which is based on the electron impact excitation. They assumed an analytical function for each excited level of the form... 

For low energy electron region, namely, below 200 x Z eV, this equation will not be valid because of the limitation of Born approximation in this energy region, the calculations will be made using electron-impact ionization and excitation cross sections for gaseous targets [7]. 

Note Differential elastic and excitation transfer cross sections have been measured for He(2 S) + Nc and for He(23S) + Ne for energies between 25 and 370 meV (1). Some of the data are shown in Fig. 52. It was possible to measure the differential excitation cross sections for the triplet system, too. A semiclassical two-state calculation was performed for the pumping transition of the red line of the HeNe-laser Hc(2 S)+ Nc— Hc + Ne(5S, lPt), which is the dominant transition for not too high energies (2). A satisfactory fit is obtained to the elastic and inelastic differential cross sections simultaneously, as well as to the known rate constant for excitation transfer. The Hc(215)+ Ne potential curve shows some mild structure, much less pronounced than those shown in Fig. 36. The excitation transfer for the triplet system goes almost certainly over two separate curve crossings. This explains easily the 80 meV threshold for this exothermic process as well as its small cross section, which is only 10% of that of the triplet system. 

The excitations of lower triplet states of benzene in these two approximations have been calculated in Ref. 133. A similar study of excitation cross sections for triplet states of a nitrogen molecule has been done in Ref. 134. 

Similar coupled-state methods, both with and without the inclusion of positronium terms, have been applied to the excitation of other alkali atoms. The results of McAlinden, Kernoghan and Walters (1994, 1997) and Hewitt, Noble and Bransden (1994) for the dominant resonant excitation cross sections for sodium, rubidium and caesium all exhibit a similar energy dependence to that for lithium. Also, the neglect of positronium terms in the expansion, as in the work of McEachran, Horbatsch and Stauffer (1991), again has the effect of increasing the low energy excitation cross sections over those obtained when such terms are included. 

Fig. 5.4. Excitation cross sections for positron-helium scattering. Experiment ...

The EMAP method has been used to compute elastic scattering and symmetric-stretch vibrational excitation cross sections for electron scattering by C02 [235], This is one of the first ab initio calculations of vibrational excitation for a polyatomic molecule. The results are in good agreement with experiment, which shows unusually large low-energy cross sections. The theory identifies a near-threshold... 

Henry et al. (10) have calculated electron-impact excitation cross sections for N(2D) and N(2P). Ali [78] has integrated these cross sections over a Boltzmann distribution to obtain the rate constants illustrated in Figure 6.5. 

Prof. R. Janev, as guest professors, worked to provide a recommended data set for electron impact ionization and excitation cross-sections for He atoms [9]. 

Ne LIF used to measure electron excitation cross-sections for Ne 44... 

Fig. 20. Velocity dependence of ionization and excitation cross sections for several fast nonalkali collisions with N2 and O2, measured using a fast alkali metal atom beam apparatus of Boitnott and Savage. ...

The effective excitation cross section for the shell under consideration which, in the case of X-ray excitation is maximum when the incident energy 0 is just above the excitation energy level W. ... 

Figure 1. A comparison of experimental and theoretical vibrational excitation cross sections for N2 scattering.

Apparent excitation thresholds and absolute excitation cross sections for He-He,... 

The polarization of the photoelectron spin in atomic and molecular photoionization processes encodes supplementary information about the relative magnitudes of electron transition moments. In atoms, the spherical symmetry permits complete characterization of the transition moments that contribute to the total excitation cross section for each resonance (Heinzmann, 1980). However, in molecules, the Z-mixing caused by the absence of spherical symmetry makes it impossible to completely characterize a resonance excitation mechanism from partial cross sections, angular distribution, and spin-polarization measurements. 

Prineiples and Methods for Measurement of Electron Impact Excitation Cross Sections for Atoms and Molecules by Optical Techniques, A. R. Filippelli, Chun C. Lin, L. W Andersen, and J. W McConkey... 

Figure 13 Plots of ( m—cwk) vs. for an analysis of the de-excitation cross section excitation cross section for the metastable helium atoms is assumed to represent the exchange part of the total de-excitation cross section. (From Ref. 142.) The values are for He(2 S) (O) and He (2iS) ( ). 

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