Ejection yields

The results presented here show that the energy distributions of the parent molecular species, e.g. benzene, are narrower than those of atomic species, even though the ejection processes in both cases arise from energetic nuclear collisions. The bonding geometry also Influences the ejection yield and angular distribution. The specific case of it-bonded and o-bonded pyridine on a metal surface is discussed with comparisons between the calculated results and experimental data. 

Ion ejection The efficiency of mass-selective radial ion ejection was 44% relative to the number of ions detected under mass-independent ion ejection conditions, yielding an overall efficiency of 12.7%. Mass-selective axial ejection yielded an overall extraction efficiency of 8% at 5.0 x 10 " Torr to 18% at 1.2 X 10 Torr. The ejected ion signal intensity increased threefold as the auxiliary AC frequency was increased from 334 to 762 kHz. 

Fig. 1. Ejection yields. Average number of Cu atoms which eject per incident Ar" ion versus the range parameter B of the Ar-Cu" interaction potential. (a) Absolute yields for the (111) and (001) faces. (b) Ratio of the yield from the (111) face to the yield from the (001) face.

Fig. 2. Ejection yield versus well depth, D, of the Cu-Cu pair potential.

If the liquid that is being bombarded contains ions, then some of these will be ejected from the liquid and can be measured by the mass spectrometer. This is an important but not the only means by which ions appear in a FAB or LSIMS spectrum. Momentum transfer of preformed ions in solution can be used to enhance ion yield, as by addition of acid to an amine to give an ammonium species (Figure 4.3). 

The physical removal of surface material is called sputtering, where energetic, chemically inert ions such as Ar" or Xe" are accelerated toward the wafer and physically eject material from the surface. The yield is defined as the ratio of the number of ejected surface atoms to the number of incoming ions per given ion energy. 

The proposed mechanism for the Conrad-Limpach reaction is shown below. Condensation of an aniline with a 3-keto-ester (i.e., ethyl acetoacetate 5) with loss of water provides enamino-ester 6. Enolization furnishes 10 which undergoes thermal cyclization, analogous to the Gould-Jacobs reaction, via 6n electrocyclization to yield intermediate 11. Compound 11 suffers loss of alcohol followed by tautomerization to give 4-hydroxy-2-methylquinoline 7. An alternative to the proposed formation of 10 is ejection of alcohol from 6 furnishing ketene 13, which then undergoes 671 electrocyclization to provide 12. 

Condensation of 2-aminothiophenol with the /3-chlorocinnamaldehyde in the presence ofp-toluene sulfonic acid (PISA) gave good yield of benzothia-zole (Scheme 14). The mechanism suggested in this work is beUeved to proceed via a nucleophilic attack of the sulfur atom in an addition-ehmination sequence followed by a spontaneous cyclization and ejection of acetaldehyde [15]. These investigations were performed in a domestic microwave reactor and need 1.5 min for completion (65% yield). Here again, oil bath heating seems to be inferior, providing a maximum conversion of 53% after... 

In an analogous process, the reactions of unsubstituted and 2-substituted allyl phenyl sulfides with (TMSlsSiH give a facile entry to allyl fns(trimethylsilyl) silanes in high yields (Reaction 26). In this case, the addition of (TMSlsSi radical to the double bond is followed by the S-scission with ejection of a thiyl radical, thus affording the transposed double bond. Hydrogen abstraction from (TMSlsSiH by PhS radical completes the cycle of these chain reactions. ... 

A radical carboxyarylation approach was introduced as the key step in the total synthesis of several biologically important natural products (Scheme 27). Treatment of thiocarbonate derivatives 112 (R = Me or TBS) with 1.1 equiv of (TMS)3SiH in refluxing benzene and in the presence of AIBN (0.4 equiv added over 6h) as radical initiator, produced compound 113 in 44% yield. This remarkable transformation resulted from a radical cascade, involving (TMSlsSi radical addition to a thiocarbonyl function (112 114), 5-era cyclization (114->115) and intramolecular 1,5-ipso substitution (115 116) with the final ejection of (TMSlsSiS radical. 

In liquefied rare gases (LRG) the ejected electron has a long thermalization distance, because the subexcitation electrons can only be thermalized by elastic collisions, a very inefficient process predicated by the small mass ratio of the electron to that of the rare gas atom. Thus, even at a minimum of LET (for a -1-MeV electron), the thermalization distance exceeds the interionization distance on the track, determined by the LET and the W value, by an order of magnitude or more (Mozumder, 1995). Therefore, isolated spurs are never seen in LRG, and even at the minimum LET the track model is better described with a cylindrical symmetry. This matter is of great consequence to the theoretical understanding of free-ion yields in LRG (see Sect. 9.6). 

The essence of the XSW technique now lies in the effect these modulations have on the photoelectric cross-section of a target atom a distance c above the mure surface. The incident X-rays can eject a core electron from the atom so generating a vacancy and resulting in the emission of a fluorescent X-ray photon The probability of an incident photon ejecting the core electron, the photoelectric cross-section, is directly proportional to the electric field experienced by the atom Hcncc. the fluorescence yield, T(0.for an atom or ion distribution A (z) a distance above the mirror surface can be written... 

Furyllithium reacts rapidly with trialkylborons though the furylborons 91 believed to be formed are not actually isolated. Treated with an electrophile (iodine or A-chlorosuccinimide), they transfer one alkyl residue to the furan ring and eject the boron residue in a reaction well known in other series (Scheme 46). The 2-alkylfurans are indeed produced in excellent yields and the method is better than many other syntheses.236... 

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