Metastable atom electron spectroscopy

Fig. 3.24 Electron energy scheme explaining the principle behind metastable atom electron spectroscopy. An excited atom M collides gently with an adsorbed molecule A the metastable atom is de-excited by electron transfer from the adsorbate to the core hole...

Perming ionization electron spectroscopy (PIES), also referred to as metastable atom electron spectroscopy... 

ADE = adiabatic detachment energies ESC A = electron spectroscopy for chemical analysis HOMO = highest occupied molecular orbitals MAES = metastable atom electron spectroscopy MIES = metastable ionization electron spectroscopy OAT = oxygen atom transfer PES = photoelectron spectra PEI = pulsed field ionization PIES = Penning ionization electron spectroscopy QM = quantum-mechanical REMPI = resonantly enhanced multiphoton ionization SC = semiclassical VDE = vertical detachment energies XPS = x-ray photoelectron spectroscopy ZEKE = zero electron kinetic energy Cp = cyclopentadienyl, Ph = phenyl, CeHs Tp =... 

Penning ioni2ation electron spectroscopy is also called (i) metastable atom electron spectroscopy (MAES), (ii) metastable deexdtation spectroscopy (MDS), (iii) metastable quenching spectroscopy (MQS), and (iv) metastable impact electron spectroscopy (MIES), where atom at metastable state is used instead of photon to ionize the target material When a slow, long-lived, electronically excited metastable atom hits a solid surface, most of its excitation energy is used to eject electrons from the surface. Unlike photons used for UPS, metastable atoms do not penetrate into the bulk of the solid. PIES, therefore, excites the outermost surface layer selectively (39). 

Iwahashi, T., Nishi, T., Yamane, H., Miyamae, T., Kanai, K., Seki, K., Kim, D. and Ouchi, Y, Surface structural study on ionic liquids using metastable atom electron spectroscopy, J. Phys. Chem. C113,19237-19243 (2009). 

Figure 7.38. XPS spectrum of an ionic liquid, [EMIM][Tf2N], detailing the C(ls) and N(ls) regions. Since there are no peaks from the Au substrate, the film thickness is hkely >10nm. Also shown (right) is the comparison between XPS, ultraviolet photoelectron spectroscopy (UPS, Hel = 21.2eV, Hell = 40.8 eV radiation), and metastable impact electron spectroscopy (MIES). Whereas XPS and UPS provide information from the first few monolayers of a sample, MIES is used for zero-depth (surface only) analysis, since the probe atoms are excited He atoms that interact with only the topmost layer of sample. Full interpretations for these spectra may be found in the original work Hofft, O. Bahr, S. Himmer-lich, M. Krischok, S. Schaefer, J. A. Kempter, V. Langmuir 2006, 22, 7120. Copyright 2006 American Chemical Society.

INS is very similar to MIES (metastable impact electron spectroscopy) or PIES (penning ionisation electron spectroscopy) except that in INS ions are used instead of metastable atoms. 

Because UPS delivers information from several top atomic layers, it is difldcult to characterize trace amounts of adsorbates. This limitation can be overcome e.g. by photoemission of adsorbed xenon (PAX) [90]. This technique is a site-selective titration technique, in which Xe adsorption sites are revealed by means of UPS it has been used effectively to characterize catalytic systems [91, 92]. An alternative surface sensitive technique capable of determining trace amounts of adsorbates is metastable impact electron spectroscopy (MIES). 

Metastable impact electron spectroscopy MIES (MAES) Metastable rare gas atom 19.81 eV (Hel Si)... 

Electron spectroscopic techniques are based on determination of the energy distribution of electrons released in the ionization process. Two of these techniques became very popular among chemists and molecular physicists, namely photo-clectron spectroscopy (PES) and X-ray electron spectroscopy also termed electron spectroscopy for chemical analysis (ESCA) Penning ionization electron spectroscopy (PIES) is related to PES, but the target molecule is ionized by electronically cxcital (metastable) atoms of a noble gas, mostly He, Ne and Ar instead of the photons used in PES. PIES is not sudi a widely used tedmique as PES and ESCA, but probably the most attractive one for vdW molecules. 

In recent years numerous investigations of clean and adsorbate covered substrates have been carried out by different methods. As most investigations use methods which give information about the behavior in at least a few layers below the surface, there is, in comparison, not so much knowledge about the electronic properties at the surface. A distinct surface sensitivity can be achieved by electron emission caused by impact of metastable noble gas atoms, a method called metastable de-excitation spectroscopy (MDS) (see, e.g., [7-9]). This technique probes predominantly the outermost atomic layer which will be demonstrated in Sect. 5.1.2 in Chap. 5. 

Harada, Y., Masuda, S., and Ozak, H. (1997) Electron spectroscopy using metastable atoms as probes for solid surfaces. Chem. Rev., 97, 1897-1952. 

There are several cascade codes developed for reproducing the cascade decays of exotic atoms (see, e.g., Borie and Leon 1980 Markushin 1999 Jensen and Markushin 2002). The cascade process is studied by detecting X-rays and Auger electrons from transitions in all exotic atoms and via laser spectroscopy in metastable antiprotonic helium (see O Sect. 28.6.3.2). It was experimentally observed that medium-heavy muonic atoms such as p Ar lose all atomic electrons via Auger effect by the time the muon reaches the ground state (Bacher et al. 1988). 

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