Appearance potentials

APS Appearance potential spectroscopy (see AES) Intensity of emitted x-ray or Auger electrons is measured as a function of incident electron energy Surface composition... 

Appearance energy. The minimum energy that must be imparted to an atom, molecule, or molecular moiety in order to produce a specified ion. The use of the alternative term appearance potential is not recommended. 

AES = auger electron spectroscopy APS = appearance potential spectroscopy CEELS = characteristic electron energy-loss spectroscopy ... 

The energy difference between diazirine and diazomethane, interesting from the point of view of their isomerism, came from MS measurements (63JCP(39)3534). The appearance potentials of the CH2 ion, common to both compounds, yielded a difference in heats of formation of 125kJmor A strong peak in the mass spectrum of 3-chloro-3-methyl-diazirine (50) with relative mass 55 was ascribed to the methyldiazirinium ion (51). 

AEAPS Auger electron appearance potential spectroscopy... 

Auger Electron Appearance Potential Spectroscopy (AEAPS)... 

Appearance potential methods all depend on detecting the threshold of ionization of a shallow core level and the fine structure near the threshold they differ only in the way in which detection is performed. In all of these methods the primary electron energy is ramped upward from near zero to whatever is appropriate for the sample material, while the primary current to the sample is kept constant. As the incident energy is increased, it passes through successive thresholds for ionization of core levels of atoms in the surface. An ionized core level, as discussed earlier, can recombine by emission either of a characteristic X-ray photon or of an Auger electron. 

Low ionizing potentials or soft ionization methods are necessary to observe the parent ions in the mass spectra of many S-N compounds because of their facile thermal decomposition. Mass spectrometry has been used to investigate the thermal breakdown of S4N4 in connection with the formation of the polymer (SN). On the basis of the appearance potentials of various S Ny fragments, two important steps were identified ... 

The combination of the flash vacuum pyrolysis (FVP) technique169 with mass spectrometry proved to be particularly useful in identification and characterization of both the fragmentation/rearrangement patterns, intermediates and/or final products formed (see Section IV.E.l). Usually, no structures are indicated in the mass spectra, although ionization and appearance potential can, in principle, provide structural information. 

In the electron impact mass spectrum of C02, 0+ ions are formed with an appearance potential (AP) 19.1 e.v. according to the process ... 

Both ions appear at 5 volts between the chamber and trap, which corresponds to a total energy of the bombarding electrons of 5 +8 = 13.0 e.v.—i.e., it corresponds to the appearance potential of CH4+ from methane. The increase at higher energies of the curve for CH4+ is mainly caused by the increase in formation of primary ions between the chamber and trap. The curve of CH5+ at first rises with increasing voltage. 

The difference between the ionization potential of methanol (10.9 e.v.) and the appearance potential of CH2OH + (11.9 e.v.) (4) is sufficiently large that, by controlling the electron energy, Reaction I can be studied to the effective exclusion of Reaction N. 

Figure 11. Breakdown diagram of ethylene. Abscissas given for ions 28 +, 27+and 26 + indicate outer and inner appearance potentials obtained by J. E. Collin (6)...

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