Resonance enhancement energy level diagrams

Figure 7. Schematic energy level diagram showing the principle of the ionization method for detecting electron transfer in gas-phase adducts. Naphthalene cation (the hole donor) is formed by resonance-enhanced two-photon ionization of the neutral. A hole acceptor, whose ionization potential is lower than that of naphthalene, is not ionized, since its S level is not resonant with the UV photons used (vi). The vibrational levels of the ionic form of the acceptor are resonant with the naphthalene cation, and accept the hole easily. Detection is by photodissociation, using photons of different frequency (V2) that dissociate the naphthalene cation in a resonance-enhanced multiphoton absorption process. Charge transfer is detected by the diminution of the product ion signal in the presence of a suitable acceptor. Adapted from Ref. [32].

The most widely used of these techniques is resonance-enhanced multiphoton ionization (REMPl) [58]. A schematic energy-level diagram of the most commonly employed variant (2 + 1) of this detection scheme is illustrated in the... 

Fig. 3. Energy level diagram for magnesium showing resonant enhancement by frequencies 2(0j and (02.

Figure 8- Partial energy-level diagrams for atomic Mg, Zn, and Hg. Levels used for two-photon resonance enhancement of 4-WSM are shown (along with corresponding wavelengths in nanometres), The regions of ionization continue and broad auto-ionizing levels that contribute to the tunability of these sources are indicated by the hatched areas.

Fig. 10. Energy level diagram for electronic resonance enhancement in the CARS spectrum of hydroxyl, OH, in which the pump laser is tuned into resonance. Strong enhancement occurs only for allowed downward Stokes transitions leading to a triplet spectrum.

Figure 12 Raman-REMPI (resonantly enhanced multiphoton ionization) spectrum of the °Qi(AJ = 0, AK = -2,K- 1) transitions of the Vie e2g) mode of benzene in a molecular beam. An energy-level diagram is shown for the double-resonance experiment. The ultraviolet source was tuned to 36,474 cm and the Raman wave-number calibration is adjusted to match the / = 6 line reported in Ref. 109. The expansion was 13% benzene in argon at 80 kPa and the sampling was done at XfD = 175 (D = 0.20 mm nozzle diameter) using pump and Stokes laser energies of 2 and 0.5 mJ. (From Ref. 117, with permission.)...

Fig. 10.1 Energy-level diagram of multiphoton ionization of molecules (a) resonance two-photon ionization (b) resonance-enhanced multiphoton ionization (REMPI) and (c) nonresonance multiphoton ionization (MPI).

Fig. 2.7 Diagram showing how resonance field ionization occurs. When an image gas atom is field ionized, the tunneling electron may be reflected right back to the atom. Field ionization is enhanced if the atomic level lines up with an energy level formed between the metal surface and the potential barrier of the applied field, as shown in the figure. The potential barrier is approximately triangular in shape.

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