Kinetic energy analysis

A time-of-flight spectrometer can be used as a mass analyzer, an ion kinetic energy analyzer, and an ion reaction time analyzer. We will consider here only what factors affect the resolution of the system in mass analysis.74 The same consideration can easily be extended to find the resolution in other analyses. There are at least two kinds of mass resolution. One refers to the ability of the system to separate two ion species of nearly equal masses in the same mass spectrum. This is related to the sharpness of the mass lines, or the full width at half maximum (FWHM) of the mass lines. The other refers to the ability of the system to distinguish two ion species of nearly identical masses, but not necessarily in the same mass spectrum. This latter mass resolution is related to the sharpness of reference points in the mass lines such as the onset flight times of the ion species, and the overall long-term stability of the system. This latter resolution determined also how accurately the instrument can measure the mass of ion species. Although this latter resolution is more closely related to ion kinetic energy analysis and is as important as the former one, we will consider here only the former kind, or the conventional kind, of mass resolution. 

In general, to improve the mass resolution of the ToF atom-probe, or for that matter any ToF spectrometer or any other instrument, one should try to identify the main sources limiting the resolution and improve from there. It is also important to consider what are the principle functions of the instrument, i.e. whether it will be used mainly for mass analysis or for ion kinetic energy analysis. For the latter purpose, an artificial flight-time-focusing scheme cannot be used. 

The magnetic sector will not separate the possible components of the M/z = 63.5 peak or of the M/z = 254 peak. The Heidelberg group of Baumann, Heinicke, Kaiser and Bethge used the electric deflection plates for a kinetic energy analysis in a manner similar to that employed by several other investigators for studies of the metastable transitions of ions with double-focusing... 

Similar arguments apply to the results (see Fig. 18) of the electric deflection analysis of the M/z = 254 ion beam. Both l2 and the formed as a result of the repulsive electron detachment from in the first field-free region (that is, I(R) ) will be transmitted by the magnetic sector. Kinetic energy analysis of this ion beam requires 2U(. to bring the I(R) species to Faraday cup 2 and to detect the l2 ion. Any formed by dissociation of I2 in the second field-free region, I(D), will be detected at Faraday cup 2 by application oiUJl to the electric deflection plates. 

Since the formation of a wide variety of doubly-charged negative monatomic ionic species is possible with a Penning ion source, and since nA beam currents of the T species may be obtained after momentum/charge and kinetic energy analysis with magnetic and electric sectors, photodetachment studies of the species... 

Propeller Power Consumption - Kinetic Energy Analysis... 

Kinetic Energy Analysis with an Electric Sector... 

The measurement is carried out in an UHV chamber. Monochromatic X-ray photons, typically from an Al-K (1486.6 eV) or Mg-K, (1253.6 eV) X-ray source, are shone at the sample to eject photoelectrons. These electrons have energies ranging from 0 eV up to almost the same energy as the incident photons but most are emitted at a few discrete energies that are characteristic of the elements present in the sample. The photoelectrons are collected by an electron energy analyser such as a hemispherical mirror analyser (HMA) to produce a spectmm of the number of electrons vs. their kinetic energy. Analysis of this spectmm provides quantitative information about the composition of the near surface region of the sample. 

Photoelectron Kinetic Energy Analysis Unimolecular Ion Decay in a Reflectron Time-of-Flight Mass Spectrometer Conclusion... 

Photoelectron spectroscopy, which is based on kinetic energy analysis of electrons ejected from an atom or molecule by an enegetic photon and provides information on the binding energies or ionization potentials of the ejected electrons. Recent developments include X-ray photoelectron spectroscopy (XPS) of surfaces, and the use of lasers as radiation sources. 

In summary, REMPI spectroscopy is now well established as a valuable method for investigating the structure and, in favourable cases, the decay dynamics of many of the long-lived excited electronic states (most notably Rydberg states) of small and medium-sized gas-phase molecules. In addition, for example, structural data for the resulting ions and/or insight into molecular photoionization dynamics can be obtained when the method of REMPI is combined with kinetic energy analysis of the accompanying photoelectrons (see Section 9.3). 

Figure 9 Anion photoelectron spectroscopy. Its unique features are (I) Intrinsic mass selectivity and (ii) neutrals as final states. Here, as an example the results for compounds of iron, carbon and hydrogen are shown which exist in catalytic processes, high-temperature terrestrial or low-temperature astrophysical chemistry. Bottom spectrum a primary anion mass spectrum containing anions of the complexes of interest. Top spectra anion photoelectron spectra obtained by electron kinetic energy analysis after laser-induced photodetachment. They reveal the change of molecular structure and electronic energies for increasing numbers of hydrogen atoms in the complex.

The time-of-flight (TOE) of an energetic electron over a distance of a few centimetres is very short, consequently, electronics with a response time of the order of nanoseconds are needed. This sort of kinetic energy analysis has not gained widespread application in the conventional techniques. 

Eland JHD (1972) Predissociation of triatomic ions studied by photoelectron photoion coincidence spectroscopy and photoion kinetic energy analysis. International Journal of Mass Spectrometry and Ion Processes 9 397-406. 

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