Zero kinetic energy photoelectron spectroscopy, ZEKE

Photoelectron spectroscopy (PES, a non-mass spectral technique) [87] has proven to be very useful in providing information not only about ionization potentials, but also about the electronic and vibrational structure of atoms and molecules. Energy resolutions reported from PES are in the order of 10-15 meV. The resolution of PES still prevents the observation of rotational transitions, [79] and to overcome these limitations, PES has been further improved. In brief, the principle of zero kinetic energy photoelectron spectroscopy (ZEKE-PES or just ZEKE, also a nonmass spectral technique) [89-91] is based on distinguishing excited ions from ground state ions. 

ZEKE (zero kinetic energy) photoelectron spectroscopy has also been applied to negative ions [M]. In ZEKE work, the laser wavelengdi is swept tlirough photodetachment thresholds and only electrons with near-zero kinetic energy are... 

Much higher resolution is achievable using threshold photoelectron spectroscopy (TPES). As noted in Chapter 9, the most widely used and successful (laser-based) TPES technique is generally referred to as ZEKE (zero kinetic energy) photoelectron spectroscopy (MuUer-Dethlefs and Schlag, 1998). The resolution achievable with this technique is limited only by the bandwidth of the laser used, and this is typically 0.2 cm or, in the most favourable case, 0.001 cm . ... 

ZEKE Zero kinetic energy photoelectron spectroscopy spectroscopy ... 

Time-of-flight mass spectrometers have been used as detectors in a wider variety of experiments tlian any other mass spectrometer. This is especially true of spectroscopic applications, many of which are discussed in this encyclopedia. Unlike the other instruments described in this chapter, the TOP mass spectrometer is usually used for one purpose, to acquire the mass spectrum of a compound. They caimot generally be used for the kinds of ion-molecule chemistry discussed in this chapter, or structural characterization experiments such as collision-induced dissociation. Plowever, they are easily used as detectors for spectroscopic applications such as multi-photoionization (for the spectroscopy of molecular excited states) [38], zero kinetic energy electron spectroscopy [39] (ZEKE, for the precise measurement of ionization energies) and comcidence measurements (such as photoelectron-photoion coincidence spectroscopy [40] for the measurement of ion fragmentation breakdown diagrams). 

The factor limiting the resolution in ultraviolet photoelectron spectra is the inability to measure the kinetic energy of the photoelectrons with sufficient accuracy. The source of the problem points to a possible solution. If the photoelectrons could be produced with zero kinetic energy this cause of the loss of resolution would be largely removed. This is the basis of zero kinetic energy photoelectron (ZEKE-PE) spectroscopy. 

Use of the supersonic jet in many branches of spectroscopy continues to increase. One technique which has made a considerable impact in recent years is that of zero kinetic energy photoelectron (ZEKE-PE) spectroscopy. Because of its increasing importance and the fact that it relates closely to ultraviolet photoelectron spectroscopy (UPS), which is described at length in earlier editions, I have included the new technique in Chapter 9. 

Muller-Dethlefs K and Schlag E W 1998 Chemical applications of zero kinetic energy (ZEKE) photoelectron spectroscopy Angew. Chem.-Int. Edit. 37 1346-74... 

Recently, zero kinetic energy (ZEKE) photoelectron spectroscopy has been used to study the OH/NH tautomerism of 2-pyridone in the gas phase (95JPC8608). This work, which is expected to develop considerably, provides a wealth of information about that equilibrium for the states So, Sj, and Do (cation ground state). 

B. Zero Kinetic Energy Threshold Photoelectron Spectroscopy and Pulsed Field Ionization (ZEKE-PFI)... 

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 =... 

ZEKE-PEl zero kinetic energy pulsed field ionization photoelectron spectroscopy... 

Photoelectron spectroscopy performed at a sufficiently high resolution provides quantitative information of the rovibronic populations of the molecular species under investigation. With the recent development of the PFI technique [185], a version of the zero-kinetic-energy (ZEKE) PE technique [186,187], the attainable resolution of PE spectroscopy has approached that of optical spectroscopy. The possibility of using PFI-PE as an alternative for the LIF technique to probe nascent-product rovibronic state distributions has become a reality [188],... 

The resolution of photoelectron spectroscopy was dramatically improved when a threshold technique called ZEKE spectroscopy was introduced. With this technique, a tuneable laser is scanned over the thresholds for the formation of specific ionic eigenstates. The resulting photoelectrons possess very low ( zero ) kinetic energies and can be discriminated from higher kinetic energy electrons, which are also produced as the photo-excitation laser is scanned over the ionic eigenstates. 

Since then the ultrafast dynamics of a few molecular, especially dimer, systems have been studied. Zewail observed the vibrational and rotational revival of excited I2 [21-23]. Stolow studied the same system, applying femtosecond pump probe zero-kinetic-energy (ZEKE) photoelectron spectroscopy [24, 25]. Gerber observed fascinating features in the ultrafast dynamics of the sodium dimer s multiphoton ionization (MPI) (see Fig. 1.1a), induced... 

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