Auto-ionizing resonances

It is emphasized in Ref. 187 that very flexible basis sets are required to deal with the finite-basis 0-dependence of the complex eigenvalues in CCR methods, and in particular to converge the resonance widths. However, the term very flexible is used in comparison to standard basis sets for valence anions, and in fact good results are obtained for auto-ionizing resonances of He, H , and Be using the aug-cc-pVTZ-l-[3s3p] basis,which includes three even-tempered diffuse s and p shells. This is not much different from the basis sets recommended here for proper description of loosely-bound electrons in general gas-phase calculations. 

Since this methodology is fairly new to mainstream quantum chemistry, it is impossible to provide a broad overview of its performance at this time, so let us close this section instead with a provocative example, illustrating the fundamental importance of such methods. Earlier in this chapter, we introduced p-coumaric acid as a molecule with an auto-ionizing resonance, in the sense that its bright state lies above its adiabatic electron detach-... 

The long-lifetime resonances (e.g., low energy resonances in02, NO, CeHe, etc.) correspond to auto-ionization states AB (Vj) with much longer lifetime (t = 10 " -10 s). 

Y.I. Heller, V.F. Lukinykh, A.K. Popov, V.V. Slabko, Experimental-evidence for a laser-induced auto-ionizing-Kke resonance in continuum, Phys. Lett. A 82 (1981) 4. 

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.

The lower trace in Fig. 10A shows the number of ions Nign(2v2) produced with LI off. The peaks correspond to resonant transitions (4), as could be proved by observation of the corresponding fluorescence (lowest trace in Fig. 10B). When the pump laser LI is switched on, the upper trace in Fig. 10A is recorded. The difference between the two curves (note that the upper curve is vertically shifted by an amount indicated by the arrow in order to separate the two recordings) gives the number of ions produced by one photon hvg on a transition from a labelled level (v, J ) in the intermediate state. The auto-ionization lines can be seen superimposed on a continuum which increases with decreasing wavelength Aj. The continuum is attributed to the direct photoionization process (3) and from its onset at... 

The focus of this chapter has been on the synthesis of new catalysts by parallel and combinatorial methods. Another aspect important to the development of new catalysts by these methods is the screening of these large libraries. We will not attempt to cover this topic comprehensively but do feel it is necessary to summarize some of the approaches that have been taken. Methods for screening libraries can be divided into both serial and parallel methods. Generally, the serial methods are adaptations of standard methods that allow for rapid individual analysis of each member of a library. Serial approaches for the analysis of libraries can be as simple as use of an auto sampler on a GC or HPLC system or as advanced as laser-induced resonance-enhanced multiphoton ionization of reaction products above the head-space of a catalyst (16) or microprobe sampling MS (63). The determination of en-antioselectivity in catalysis is a particular problem. Reetz et al. (64) reported the use of pseudoenantiomers and MS in the screening of enantioselective catalysis while Finn and co-workers (65) used diastereoselective derivatization followed by MS to measure ee. 

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