Secondary ionizations

Surface Analysis by Laser Ionization Post-Ionization Secondary Ion Mass Spectrometry Multi-Photon Nonresonant Post Ionization Multiphoton Resonant Post Ionization Resonant Post Ionization Multi-Photon Ionization Single-Photon Ionization... 

Due to the high mass, low volatility, and thermal instability of chlorophylls and derivatives, molecular weight determination by electron impact (El) MS is not recommended. Desorption-ionization MS techniques such as chemical ionization, secondary ion MS, fast-atom bombardment (FAB), field, plasma- and matrix-assisted laser desorption have been very effective for molecular ion detection in the characterization of tetrapyrroles. These techniques do not require sample vaporization prior to ionization and they are effective tools for allomerization studies. 

As with pseudo-a-cleavage, the suppression of SHT and DHT by N-alkylation reflects the reduced tendency of ionized secondary and especially tertiary amines to undergo the initial hydrogen transfer steps to form DIs44. This common trend also supports the contention that ionized amines generally isomerize via DIs. 

The solution will have a very strong alkaline reaction, since it contains a large fraction of 1 mole each of ionized NaOH and of ionized secondary sodium phosphate, Na2HPC>4. The OH- ions thus formed check the hydrolysis of the secondary sodium phosphate but if solid secondary sodium phosphate is dissolved in water, hydrolysis of this salt ensues to a sufficient extent to make the solution alkaline to litmus. 

Spontaneous ionization requires both good leaving groups and that the resulting carbenium ions are sufficiently stable. For example, although primary triflates are very stable covalent species which do not self-ionize, secondary triflates with phenyl substitents are very reactive and spontaneously ionize. The ionization equilibrium of styryl triflate could not be established because of side reactions such as Friedel-Crafts alkylation [56], On the other hand, methoxymethylium triflate is partially ionized with equilibrium constants Kj = 5-10 4 at 10° C and Kt = 210 4 at -70° C in S02 [57]. In this system, ionization is endothermic. Secondary triflates with alkoxy substituents, such as those in polymerizations of vinyl ethers, are apparently more strongly ionized than their primary counterparts [58,59],... 

The density of excitation and ionization is not necessarily the same for all radiation qualities. For example, it is greater along the track of an a-par-ticle than for an electron track. For a primary-recoil electron produced by Co 7-rays in water, the distance between successive ionizations is about 1000 A. TTie ionized track is, therefore, sparse. At each point of ionization, secondary electrons give rise to further ionizations, forming a group of ion-pairs. In contrast, a-particles form a continuous track as a result of overlapping between the spheres of ionization. 

It was reported that a series of linear polyethylenimines (PEIs) with various molecular weights were synthesized and used to prepare polypseudorotaxanes with a-CD [81]. The PEIs were found to form stable polypseudorotaxanes at suitable pH and/or temperature, because PEIs have ionizable secondary amino groups pK = 8.9), which play a role of an energy barrier for the polypseudorotaxane formation. 

The cleavage of esters in basic medium, mediated by CDs, is the system most studied. In some cases, such as that with meta-substituted phenyl acetates, cleavage is strongly accelerated on the contrary, the reaction of para-substituted isomers is accelerated only modestly. The observed effects depend on the chain length of the ester, the CD, and the position of the substituent on the phenyl group. The mechanism typically involves nucleophilic attack by the ionized secondary hydroxyl groups of CD, but in other cases, general base catalysis competes with nucleophile catalysis. 

Mass spectrometry of secondary ions (SIMS) [78, 79] or of post-ionized secondary neutral particles (SNMS) [80-82], which both are ejected from a surface which is bombarded with an ion beam, is a very sensitive but for chemical compounds also destructive analytical technique. It yields excellent qualitative information. Quantitative results are difficult to obtain. A review is given in [83]. 

When the ions (primary ions) having high energies are irradiated on the sample surfaces in a vacuum, some of the atoms of the samples are ionized (secondary ions). Secondary ion mass spectrometry (SIMS) [8] is the mass spectrometry of secondary ions. SIMS is not a nondestructive analysis, but a method for depth-directional distribution of a micro amount of an element. 

Mass spectrometric separation of the ionized secondary species, which are sputtered atoms, molecules, clusters, according to their mass-to-charge ratios ... 

Surface-extended X-ray absorption fine structure (analysis) spectroscopy Sum frequency generation Second harmonic generation Surface ionization Secondary ion mass spectroscopy Subtractively normalized interfacial Fourier transform infrared spectroscopy Single potential alteration infrared (spectroscopy)... 

PES photoelectron spectrometer SF space focus L1-4 laser for different purposes LI resonant multiphoton ionization secondary ion excitation mass selective dissociation, electron detachment from anions anion formation, laser desorption TOF-sep mass separation by time-of-flight... 

On the other hand, ions produced in a continuous beam must be formed into pulses by an appropriate device, so an additional complication is introduced. Examples are electron ionization, secondary-ion mass spectrometry (SIMS), and most recently electrospray ionization (ESI). As mentioned above, the earliest commercial TOF instruments used electron-impact ionization, and the difficulty in producing short ion bursts with this method was mainly responsible for their limitations in mass resolution. However, new technology has enabled dramatically improved performance for continuous sources, particularly ESI, and TOF has been gaining popularity for such sources as well. 

Modem soft ionization techniques have overcome the sample volatility requirement by combining the first two steps in mass spectrometry sampling and ionization. The soft ionization techniques used for the analysis of surfactants include fast atom bombardment (FAB), field desorption (FD), desorption chemical ionization (DCI, also called direct chemical ionization), secondary-ion mass spectrometry (SIMS), and laser desorption methods. 

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