Secondary emission desorption

There is no systematic study of mass spectra of azoniaspiroalkanes. Mass spectra of Prospidine and related compounds (22), using secondary emission spectroscopy, have been reported <90OMS(25)432, 91KFZ78>. A minor adduct from prospidine and deoxyguanosine-5 -phosphate has been studied by soft-ionization mass spectrometry (Cf particle desorption mass spectrometry— PDMS) <94RCM195, 94MI 840-01 >. 

Correlations between surface species and emitted secondary ions are based on characterization of the surface adlayer by adsorption and thermal desorption measurements. It is shown that the secondary ion ratios RuC+/Ru+ and R CTVRuJ can be quantitatively related to the amount of nondesorbable surface carbon formed by the dissociative adsorption of ethylene. In addition, emitted hydrocarbon-containing secondary ions can be directly related to hydrocarbon species on the surface, thus allowing a relatively detailed analysis of the hydrocarbon species present. The latter results are consistent with ejection mechanisms involving intact emission and simple fragmentation of parent hydrocarbon species. 

The time dependence of desorption remains a little-explored but potentially useful approach for mechanistic studies. Cotter (33) has monitored secondary ion kinetic energies in a laser desorption (LD) time-of-flight instrument. Laser pulses 40 ns wide were used to desorb K+ ions from solid KC1, and the ions were sampled at variable times after the laser pulse. Emission persists for several microseconds after excitation, and secondary ion kinetic energies were found to decrease when examined at longer times after excitation. This result supports a thermal model for... 

Lead and sulphur are derived from the fuel and there is a complex equilibrium dependent upon temperatures and gas composition controlling the absorption/desorption of these poisons. In the case of lead, extended trials have demonstrated the feasibility (ref. 20) of successful operation of oxidation catalysts on leaded fuel. However, it has been noted that in the decade since introduction of lead-free fuel in the USA, residual lead levels have fallen dramatically. In that market, where leaded and unleaded fuels are both available, incidents of poisoning reflect contamination of distribution equipment or deliberate misfuelling (refs. 21,22). Sulphur may also be derived from lube oil but its impact in the sense of poisoning is low on PGM catalysts. Interaction with catalyst components can, however, influence secondary/unregulated emissions of... 

Impurity inclusions and surface defects are a cause of many difficulties to the polymer producer and user. Equipment used for studying these phenomena discussed in Chapter 4 include electron microprobe x-ray emission/spectroscopy, NMR micro-imaging, various forms of surface infrared spectroscopy, e.g., diffusion reflection FTIR, ATR, also photoacoustic spectroscopy and x-ray diffraction - infrared microscopy of individual polymer fibres. Newer techniques such as scanning electron microscopy (SECM), transmission electron microscopy, time of flight secondary ion mass spectrometry (TOFSIMS), laser induced photoelectron ionisation with laser desorption, atomic force microscopy and microthermal analysis are discussed. 

Desorption/Ionization model A model describing molecular secondary ion emission... 

Figure 1.13 Selected analytical techniques used for metallomics studies. ICP-OES, inductively coupled plasma optical emission spectroscopy, ICP-MS, inductively coupled plasma mass spectrometry LA-ICP-MS, laser ablation ICP-MS XRF, X-ray fluorescence spectroscopy PIXE, proton induced X-ray emission NAA, neutron activation analysis SIMS, secondary ion mass spectroscopy GE, gel electrophoresis LC, liquid chromatography GC, gas chromatography MS, mass spectrometry, which includes MALDI-TOF-MS, matrix-assisted laser desorption/ ionization time of flight mass spectrometry and ESI-MS, electron spray ionization mass spectrometry NMR, nuclear magnetic resonance PX, protein crystallography XAS, X-ray absorption spectroscopy NS, neutron scattering.

The physical effects that lead to the eventual desorption of secondary particles are not yet completely understood. Whereas the desorption of secondary neutrals from elemental targets can be described fairly well, an explanation of the emission of charged particles and. in particular, the emission of molecular species, is still being sought. Nevertheless, there is consensus that. sputtering is based primarily on the formation of a collision cascade in tbe target caused by the impinging primary ion 3. 4J. 

The primary-ion bombardment leads not only to the desorption of sputtered elements and molecules but also to the emission of further. secondary species, among them electrons. The number of emitted electrons per primary ion (the so called ion-induced secondary-electron coefficient) can be as large as 10 according to the particular material. Ion bombardment of insulating surfaces therefore leads to the buildup of positive charge at the surface which can se-... 

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