Excitation transfer collisions

Significant spin-orbit effects have also been observed in a number of the excited inert gas nonreactive collisional decay channels. In excitation transfer collisions between metastable argon and hydrogen atoms. 

FIGURE 2. Rotational alignment in the products of atom transfer or excitation transfer collisions involving Xe(3l ) and (a) IQ, (b) C, Data points... 

A-B relative or external motion undergo free-free transitions (E., E. + dE.) (Ej Ej+ dE within the translational continuum, while the structured particles undergo bound-bound (excitation, de-excitation, excitation transfer) or bound-free (ionization, dissociation) transitions = (a, 3) ->/= (a, (3 ) in their internal electronic, vibrational or rotational structure. The transition frequency (s ) for this collision is... 

Ne is metastable neon produced by electron impact. Ne transfers its excitation to hydrogen molecules. The hydrogen molecules participating in these energy transfer collisions are produced in highly excited preionized states which ionize after a time lag sufficient to permit the initial neon and hydrogen collision partners to separate. The hydrogen ion is formed in the v = 5 or 6 quantum states and reacts with a second neon... 

Returning to our A-B dissociation process, the vibrational levels of the molecule can only be excited by collisions with other molecules. Consider the energy transfer of molecule A by collision with other A molecules as a chemical reaction... 

The problem of quenching alkali resonance radiation in E-VR energy-transfer collisions with simple molecules is important as a model case for basic processes in photochemistry and serves its own right for a variety of practical applications, such as in laser physics. It has been studied for many years in the past, but only recent progress has led to information of the final internal energy of the molecule. In particular, crossed-beam experiments with laser-excited atoms allow a detailed measurement of energy-transfer spectra. There can be no doubt that the curve-crossing... 

Figure 28. Electron spectrum for collision system He -Kr at various collision energies. Broad distribution at low electron energies is a result of Penning ionization, and narrow peaks arise from atomic autoionization of krypton following excitation transfer from He to Kr.77...

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...

In principle, excitation transfer at curve crossings may also occur at thermal collision energies, but only under rather restricted conditions, because at low collision energies the system will usually follow the adiabatic curve V (R)- The following two exceptions may arise ... 

The interactions between metastable noble-gas atoms and ground-state noble-gas atoms are relatively simple and have been investigated quite extensively. If the excitation energy is lower than the ionization potential of the collision partner, the only important inelastic process is the transfer of excitation energy.12 The excitation transfer is usually very efficient when the process is near resonant. The process that is responsible for the operation of the He-Ne laser,13... 

In the projection operator formalism, which leads to a rigorous basis for the optical potential, the absorptive imaginary part is associated with transitions out of the elastic channel from which no return occurs. Whereas Pgl transitions are in this category, excitation transfer (ET) transitions are not, since return ( virtual excitation ) can occur during the ET collision. In the event that a localized avoided curve crossing with one other state dominates the inelastic process (expected for many endoergic transfers), the total absorption probability (opacity) can still be defined ... 

The branching ratio is 1 1000 in favor of the ground state. The beam is scattered from a second supersonic beam, and the electronically excited atoms are detected. As excitation transfer can occur during the collision (e.g., He + Ne— He + Ne ), a second quench lamp is sometimes installed in front of the detector, to enable study of the energy-transfer process separately. 

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