First ionization

Merkle, R., Savin, A., Preuss, H., 1992, Singly Ionized First-Row Dimers and Hydrides Calculated With the Fully Numerical Density Program NUMOL , J. Chem. Phys., 97, 9216. 

Indeed, by using soft El ionization, we have been able to unambiguously detect products from all five reaction pathways (2a)-(2e), determine their branching ratio and characterize their dynamics.34 Here we discuss some of the results that we have obtained on this reaction, which well exemplify the power of soft El ionization. First of all, from measurements of the El efficiency curves at various to/e ratios (15, 42, and 43), we have found that the parent ion at m/e = 43 (CH2CHO+, corresponding to one of the main reaction channels, the vinoxy radical,) is not stable, so measurements of angular and TOF distributions were carried out at m/e = 42. Incidentally, from the El ionization efficiency curve at m/e = 42 we have obtained some direct information on the IE of the vinoxy radical, for which no such information was available till now. The IE should be <11 eV. 

For most of the molecules, the electron flow is from D to A, which is supported by the anti-Aviram-Ratner mechanism of Fig. 11a. However, there may be yet another possibility, shown in Fig. 21 implicit in the analyses of Figs. 9-11 has been the Aviram and Ratner assumption [79] that auto-ionization is a less efficient competing process. If the electric field induces intramolecular ionization first by sufficiently altering the orbital energies, then the direction of electron flow may occur in the anti-AR direction (Fig. 21) ... 

Hitherto the discussion of Fig. 5.2 has neglected the possibility of non-radiative decay following 4d shell excitation/ionization. These processes are explained with the help of Fig. 5.2(h) which also reproduces the photoelectron emission discussed above, because both photo- and autoionization/Auger electrons will finally yield the observed pattern of electron emission. (In this context it should be noted that in general such direct photoionization and non-radiative decay processes will interfere (see below).) As can be inferred from Fig. 5.2(h), two distinct features arise from non-radiative decay of 4d excitation/ionization. First, 4d -> n/ resonance excitation, indicated on the photon energy scale on the left-hand side, populates certain outer-shell satellites, the so-called resonance Auger transitions (see below), via autoionization decay. An example of special interest in the present context is given by... 

The rare gas atom (R) with the higher IP is ionized first, followed by a charge transfer to the polyatomic molecule. This can either involve a direct charge transer ... 

The theoretical relation, Ve — hv, has been abundantly checked in measurements of spectroscopy and physics but its direct application to complex molecules in chemical reactions has not been established. Bombardment of mercury atoms or other simple atoms at low pressures by electrons under controlled voltages causes the emission of monochromatic light at the wave lengths predicted by this formula. Moreover, the ionization potential, at which the electron is completely separated from its atom, corresponds directly to the wave length at which the discrete lines of the spectrum merge into a continuous spectrum. This continuous spectrum is due to the fact that the kinetic energy of the expelled electron and ion is not quantized. The close agreement between the ionization potential and the lowest frequency of continuous absorption, where ionization first starts, constitutes another proof of the relation Ve — hv. 

The ionization of monoprotic acids and bases and hence their solubility and absorption is dependent on their pK, the pH at which the drug is 50% ionized. First developed by Hammett and published in 1940, the relation between the dissociation constants of benzoic acid derivatives and the longer range electronic (inductive, mesomeric and field) effects is linear and additive. 

Passive chemical ionization mass spectrology. It is the term used for chemical ionization. First of all we invented the term passive because we were using already existing natural ions, and then after we employed this method by which we formed ions in the atmosphere and we measured them. 

The ionizable hydrogens are lost in order of acidity, the most acidic ionizing first. 

Explain in molecular orbital terms the changes in H—H internuclear distance that occur as the molecular H2 is ionized first to Hj and then to H. ... 

PES band of the Mo=Mo triply bonded compound245 presumably contains both 7rMoMo and crMoC ionizations245 and in the rj5-C5H5 vanadium derivative241, the 3dv electrons are ionized first. 

Thermospray ionization First to interface with HPLC, quasimoleular ions, +ve or—ve... 

Electron ionization (El) is one of the oldest modes of ionization, first used by Dempster in 1918 [1], It is the most popular means of ionization for organic compounds with molecular mass less than 600 Da. Several other classes of compounds can also be analyzed conveniently by EI-MS. It is, however, restricted to thermally stable and relatively volatile compounds. Many solids and liquids are quite volatile at the prevailing vacuum of the instrument, whereas others must first be vaporized at elevated temperatures. 

DMAPP may act as an alkylating agent (isopropene unit) via an 8 2 nucleophilic displacement in which the diphosphate is the leaving group. In some cases, DMAPP may ionize first to the resonance-stabilized allylic carbocation, and thus an S l reaction occurs on the C-activated position (Figure 1.12). 

Electron ionization, first modern mass spectrometer A. Dempster [49]... 

Dopants are ionized first, followed by the ion-molecule reaction with solvent (S). Proto-nated solvent ions are generated, and subsequently they transfer protons to the analytes. 

The carboxyl ionization [pK]) is low and easily identified. However, the ammonium and thiol groups have similar pK values (compare methylamine with methyl mercaptan, Table 2.1) and so an uncertainty exists as to which group ionizes first. Ki, K2, and K3 represent macroscopic ionization constants determined experimentally from a titration curve. K2 and are the composite of four microscopic ionization constants. Once the proton is lost from the carboxyl group, one of two ionization pathways may be followed ... 

Each element has characteristic first and second ionization potentials that are dependent on the electronic structure of that specific element. The higher the ionization potential, the more externally applied energy is required to induce ionization. First and second ionization potentials for the elements are tabulated in Appendix 1. Energy for ionization can be applied... 

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