Kinetic energy, photoelectron

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... 

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. 

Figure 9.50 Processes involved in obtaining (a) an ultraviolet photoelectron spectrum, (b) a zero kinetic energy photoelectron (ZEKE-PE) spectrum by a one-photon process and (c) a ZEKE-PE spectrum by a two-photon process in which the first photon is resonant with an excited electronic state of the molecule...

Figure 9.51 A zero kinetic energy photoelectron (ZEKE-PE) resonant two-photon spectrum of 1,4-difluorobenzene in which the first photon excites the molecule of the zero-point level of the S-[ excited electronic state of the molecule. (Reproduced, with permission, from Reiser, G., Rieger, D., Wright, T.G., Muller-Dethlefs, K. and Schlag, E.W., J. Phys. Chem., 97, 4335, 1993)...

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. 

D. -S. Yang, M. Z. Zgierski, D. M. Rayner, P. A. Hackett, A. Martinez, D. R. Salahub, P.-N. Roy, and T. Carrington Jr., J. Chem. Phys., 103, 5335 (1995). The Structure of NbjO and Nb30 Determined by Pulsed Field Ionization-Zero Electron Kinetic Energy Photoelectron Spectroscopy and Density Functional Theory. 

The spectral features of XANES have been interpreted as the result of multiple-scattering resonances of the low kinetic energy photoelectrons. Examples of the strong and sharp XANES peaks above the continuum threshold and below the beginning of the weak EXAFS oscillations in the absorption spectra of condensed molecular complexes, are shown in Fig. 4.6. 

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. 

ZEKE-PES was pioneered by Miiller-Dethlefs, Sander and Schlag18,25. They and others26 recorded the zero kinetic energy photoelectrons produced by absorption of one or more photons to a resonant ion state as a function of pulsed laser excitation wavelength. ZEKE electrons were extracted by an electric field pulse which permitted a delay between the creation and collection of electrons. During this delay, non-ZEKE electrons departed the focal volume, leaving only ZEKE electrons for collection by the extraction pulse. 

Extensive attention is devoted to the interactions between aniline and aniline cation and neutral partners to form clusters which are investigated by recent techniques. In particular, van der Waals complexes between aniline and Ar, Kr, N2, CO, in both neutral and cationic forms, are studied by the technique of zero kinetic energy photoelectronic spectroscopy174. Theoretical studies175 on the aniline and aniline cation, free or complexed with a number of partners (as potential solvents) produce important results about the cluster geometry and the relative importance of different kinds of interactions. 

Using zero electron kinetic energy photoelectron spectroscopy, the structures of Nb3N2 and its cation were assigned as C2v. The two N atoms bridge two sides of an isosceles triangle of Nb atoms.603 Similar conclusions have been drawn for the Nb3C2 system and for [M30]x (x = — 1, 0, + 1).604... 

The generally strong scattering power of the atoms of the medium for low kinetic energy photoelectrons favors multiple scattering (MS) processes higher ener-... 

TP-ZEKE two-phototon zero-kinetic-energy (photoelectron spectra)... 

M. Sander, L.A. Chewier, K. MiiUer-Dethlefs, E.W. Schlag, High-resolution zero-kinetic-energy photoelectron spectroscopy of NO. Phys. Rev. A 36, 4543 (1987)... 

LASER-BASED PULSED FIELD IONIZATION-ZERO ELECTRON KINETIC ENERGY PHOTOELECTRON SPECTROSCOPY... 

High-resolution zero kinetic energy photoelectron spectroscopy... 

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 . ... 

Merkt F, Softley TP. 1992. Rotationally resolved zero-kinetic-energy photoelectron spectrum of nitrogen . Phys. Rev. A 46(1) 301-314. 

---