Total ion yield

Much of the energy deposited in a sample by a laser pulse or beam ablates as neutral material and not ions. Ordinarily, the neutral substances are simply pumped away, and the ions are analyzed by the mass spectrometer. To increase the number of ions formed, there is often a second ion source to produce ions from the neutral materials, thereby enhancing the total ion yield. This secondary or additional mode of ionization can be effected by electrons (electron ionization, El), reagent gases (chemical ionization. Cl), a plasma torch, or even a second laser pulse. The additional ionization is often organized as a pulse (electrons, reagent gas, or laser) that follows very shortly after the... 

Recently, the CH4+-CH4 reaction has been investigated (9) by measuring the CH4 + disappearance cross-section rather than CH5 + formation cross-sections. Results of this work are shown in Figure 9. Two mechanisms cause a loss of CH4 + ions from the total ion yield in the methane mass spectrum. There are loss processes in the ion source which generate new ions, CH5 +, and possibly other products. Other loss... 

Ratio of counts in peak area and total ion yield. 

The transfer of ions from atmospheric pressure to the vacuum of a spectrometer necessarily induces ion losses. But these losses are compensated by the higher total ion yield in the API source due to fast thermal stabilization at atmospheric conditions. Indeed, when the sample ionization is performed under atmospheric pressure [50,51 ], an ionization efficiency 103 to 104 times as great as in a reduced-pressure Cl source is obtained. 

K at increasing exposures (0.1L-80L) on crystalline ice films obtained by water deposition on a Pt(l 11) substrate held at 150 K. The NEXAFS measurements were performed in the total electron yield (TEY) mode using the monochromatic soft X-ray radiation of SA22 beam line of Super ACO at the LURE facility (Orsay, France). The resolution was 0.02 eV at 190 eV. The PSD NEXAFS have been measured in the total ion yield mode, using a two stages microchannel plates detector. The experimental conditions are detailed in ref 4. 

Figure 7.4. Time-of-flight secondary-ion mass spectroscopy (ToF-SIMS) image of the distribution of Fe on a cross section of a trembling aspen (Populus tremuloi desMmchx ) root embedded in clayey soil material. The Fe values are normalized to the total ion yield of the surface. The bar is 100 (im. (From Martin et al., 2004.)...

Auger processes of all kinds (spectator and resonant) are also observed in molecules [268, 269, 270, 271, 272, 273, 274]. In addition, because of the very rapid dissociation of doubly-excited states in molecular species, neutral dissociation can occur before the decay of the core hole, and has been detected in the total ion yield of the H2S molecule [275]. 

Figure 46.14 shows results of TG-MS in dry Fie flow. The simultaneous total ion current (TIC) curve (variation of total ion yield as a function of temperature) is in good agreement with the TG curve. 

The simplest signal to be measured in a time-resolved photoionization experiment is the total ion yield following the action of pump and probe pulses. It is given by the integral population of the ionization continua in the limit t —> oo. ... 

Another way to evaluate the polar fluid model is to consider its consequences for IR versus UV MALDI ion yields. Because the matrix is generally in large excess, its autoionization should dominate the total ion yield (ions/neutrals), in both MALDI variants. Instead, IR yields are orders of magnitude lower than in In addition, this... 

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