Ionisation probabilities

Table 5.4 Ionisation probabilities relative to N2 (for electron energies of 102 eV)...

At pH < 10.0, only one phenol function is ionised (probably at position 1) the two absorption peaks (X = 326 nm and X = 520 nm) can reasonably be assigned to the n-cr transition of the protonated and deprotonated forms of hydroxy groups, respectively. 

Suppose the ionisation probability per unit time of an atom is dP/dt. The number of atoms left in the ground state 0 > after a time t is... 

Neutral atom yields are high, especially for low energy incident ions. Since the ionisation probability of secondary particles obtained directly from the sputtering process is low, the yield of secondary ions can be enhanced by post-ionisation. The matrix effects occurring in SIMS are expected to be considerably smaller in SNMS and therefore quantification of the spectra to determine elemental composition may be much more accurate. 

Huyghebaert, C., Conard, T, Brijs, B., Vandervorst, W. (2004) Impact of the Ge concentration on the Ge-ionisation probability and the matrix sputter yield for a SiGe matrix under oxygen irradiation. Applied Surface Science, 231-232,708-712. 

The surface mass spectrum characterises the surface chemical structure. The spectral intensities can be used to determine the relative surface concentrations of the different surface species. Both positive and negative ion detection modes are possible in SIMS, as in all mass spectrometry techniques. A comparison of the positive and negative ion spectra can often substantially improve the analysis of the results. In SIMS, the charged fraction of the secondary particle flux is very small (10 ). Moreover, the number of sputtered ions per incident primary ion (i.e. the secondary-ion yield) is matrix dependent. With such yield variations direct quantification of surface species based on the number of desorbed secondary ions (i.e. from the SIMS data) is generally impossible [123]. Wucher et al. [143] have recently described a method to determine the secondary ion formation probability, i.e. the ionisation probability of sputtered particles in a direct and quantitative manner. 

Post-ionisation schemes for the detection of sputtered neutral species in SNMS utilise either electron impact ionisation (e-beam SNMS), elecfion gas or plasma ionisation (plasma SNMS) or laser ionisation (L-SNMS). For e-beam SNMS, which is based on the use of a directed flux of essentially mono-energetic electrons towards the sputtered neutrals, high sensitivities have been obtained. Plasma or e-gas SNMS uses a low-pressure plasma (usually inert gas, e.g. Ar) containing ions to sputter the surface and at the same time the e-gas for ionisation of the neutrals. Although e-beam and plasma SNMS suffer from a low ionisation probability, they provide a well-established quantification scheme. 

As a result a survey pattern was obtained on all species contained in the reaction, including free radicals. By changing the temperature of the reaction zone we obtained information on the temperature dependence of the cibundances of the reaction products and radicals. The results are of a semi-quantitative character because the ionisation probabilities of the species and their mass discrimination in the flow system are not known. 

This is an exothermic process, due largely to the large hydration enthalpy of the proton. However, unlike the metallic elements, non-metallic elements do not usually form hydrated cations when their compounds dissolve in water the process of hydrolysis occurs instead. The reason is probably to be found in the difference in ionisation energies. Compare boron and aluminium in Group III ... 

Concentrated solutions are here considered to be those containing > c. 89 % by weight of sulphuric acid. In these solutions nitric acid is completely ionised to the nitronium ion. This fact, and the notion that the nitronium ion is the most powerful electrophilic nitrating species, makes operation of this species in these media seem probable. Evidence on this point comes from the effect on the rate of added water ( 2.4.2)... 

Solutions of alkah metal and ammonium iodides in Hquid iodine are good conductors of electricity, comparable to fused salts and aqueous solutions of strong acids. The Hquid is therefore a polar solvent of considerable ionising power, whereas its own electrical conductivity suggests that it is appreciably ionized, probably into I" and I (triodide). Iodine resembles water in this respect. The metal iodides and polyiodides are bases, whereas the iodine haHdes are acids. 

Q4. It s another case of distinguishing two compounds but this time they aren t isomers. (Unfortunately, the mass spec next door is out of action following a sub-optimal preventative maintenance visit from the service engineer and the compounds probably wouldn t ionise anyway )... 

Experimental considerations Sample preparation and data evaluation are similar to membrane osmometry. Since there is no lower cut-off as in membrane osmometry, the method is very sensitive to low molar mass impurities like residual solvent and monomers. As a consequence, the method is more suitable for oligomers and short polymers with molar masses up to (M)n 50kg/mol. Today, vapour pressure osmometry faces strong competition from mass spectrometry techniques such as matrix-assisted laser desorption ionisation mass spectrometry (MALDI-MS) [20,21]. Nevertheless, vapour pressure osmometry still has advantages in cases where fragmentation issues or molar mass-dependent desorption and ionization probabilities come into play. 

The type of proteinaceous binder was correctly identified in all model samples. In only one case (S10), the animal glue was additionally identified, although the restorer who prepared these model samples declared that the sample contained only egg binder. It is possible that this sample was contaminated during its preparation or during laboratory treatment. The results indicate that this method does not allow reliable identification of the presence of individual egg yolk and egg white most probably it is caused by the presence of a trace of egg white that is always present in the egg yolk preparations (and vice versa) and can be detected by the highly sensitive PMM method. The identification of individual types of animal glues will never be reliable by MALDI-TOF mass spectrometry because of their similar composition the application of ESI (electrospray ionisation)-MS/MS (Section 6.5) could possibly overcome this problem. Only the fish glue, whose peptide... 

Herbig-Haro object A bright object associated with young stellar object, probably due to a region of ionisation associated with high-speed polar jets. 

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