Target-excited

Figure 2 (a) The optimized electric field as a function of time for the H2(v = 0,) = 0) — H2 (v = 0,7 = 2) rotational excitation process, (b) Absolute value of the Fourier transform of the optimized electric field, (c) The change in populations of the ground-and target excited-state shown as a function of time. Taken from Ref [24] with permission from Qinghua Ren, Gabriel G. Balint-Kurti, Frederick R. Manby, Maxim Artamonov, Tak-San Ho, and Herschel Rabitz, 7. Chem. Phys. 124, 014111 (2006). Copyright 2006, American Institute of Physics. 

Figure 20 Doubly differential cross sections for ejection of electrons of 219 eV (16 Ry) from He by 2-MeV He ions. The points are measured cross sections and the calculated results are line A— projectile ionization, target remains in the ground state line B—projectile ionization with simultaneous target excitation line C— target ionization, projectile remains in the ground state and line D—target ionization with simultaneous projectile excitation. (From Ref. 70.)...

When A and B are identical atomic species (e.g., H + -H259 or He+-He260), radiative emissions may result from neutral target excitation as well as from electron capture by the ionic projectile into the same excited state. Both processes yield Lyman a radiation in the case of H+-H collisions,259... 

As the positron energy is raised above the positronium formation threshold, EPs, the total cross section undergoes a conspicuous increase. Subsequent experimentation (see Chapter 4) has confirmed that much of this increase can be attributed to positronium formation via the reaction (1.12). Significant contributions also arise from target excitation and, more importantly, ionization above the respective thresholds (see Chapter 5). In marked contrast to the structure in aT(e+) associated with the opening of inelastic channels, the electron total cross section has a much smoother energy dependence, which can be attributed to the dominance of the elastic scattering cross section for this projectile. 

The method is based on the nearly complete cancellation between the target excitation energy and the binding energy of the attached electron for certain low-energy resonances. For a lithium-like system, a resonance can be formed in the following way ... 

Since only a relatively small number of coupled equations can be solved in practice, the target states p must be selected carefully. Virtual target excitation into the ionization continuum must be approximated by inclusion of closed-channel pseudostates that cannot be target eigenstates but have the character of wave packets in the continuum. Target polarization response is treated by including polarization pseudostates y(P). 

Virtually all non-trivial collision theories are based on the impact-parameter method and on the independent-electron model, where one active electron moves under the influence of the combined field of the nuclei and the remaining electrons frozen in their initial state. Most theories additionally rely on much more serious assumptions as, e.g., adiabatic or sudden electronic transitions, perturbative or even classical projectile/electron interactions. All these assumptions are circumvented in this work by solving the time-dependent Schrodinger equation numerically exact using the atomic-orbital coupled-channel (AO) method. This non-perturbative method provides full information of the basic single-electron mechanisms such as target excitation and ionization, electron capture and projectile excitation and ionization. Since the complex populations amplitudes are available for all important states as a function of time at any given impact parameter, practically all experimentally observable quantities may be computed. 

CASSCF is full configuration interaction (Cl) with orbital optimization in a window of partially occupied active orbitals, the active space. To choose an appropriate active space for a problem requires a model of the target excited states If the active window is not chosen correctly, then it is impossible to represent the excited state sought. 

In summary, to choose an active space for CASSCF, one needs a conceptual model of the target excited states. Part of this may come from having previously carried out some lower level of excited-state computation (Cl singles [CIS] or time-dependent density functional methods [TDDFT]), but most of it must come from experience and chemical understanding. 

Target Excitation Voltage (kV) Line Wavelength. (A) Relative Flux... 

Metal content in zeolite was detected by XRF (X-ray fluorimetry) using a tungsten target. Excitation voltage was 40 kV. Blaze current was 50 mA. The spectral line intensity was recorded on a proportional counter. 

For the 2p state, a similar behavior to the 2p excitation of the target is present. Our results are higher for low energies than that reported by the experiment due to the same reason mentioned in the case of the target excitations. 

Figure 8.11 Spectnun of 10-i nn lead in aqueous solution taken at a total count rate of 10,000 counts/s, a counting time of 300 s, filtration, and various targets (a) direct excitation with a tungsten target x-ray tube operating at 25 kV (b) secondary target excitation with a zirconium target. (Reprinted from Ref. 11 with permission from Kevex Corp., Burlingame, Calif.)...

Figure 3 Schematic view of an ED-XRF instrument configured for secondary target excitation. The tube-secondary target-sample-detector path is designed to have a Cartesian arrangement to suppress scatter of tube radiation into the detector.

Some of the more specialized applications of ED-XRF instrumentation have been summarized in previous sections. Further examples, mainly relevant to direct tube and secondary target excitation using Si(Li) detectors, are summarized here. 

---