Breakdown curve

The pyrolysis breakdown behavior for cubane is plotted in Fig. 4.7. Cubane is found to be stable on the millisecond time scale for temperatures up to 500 K. Minor decomposition was found between 500 and 700 K, and above that point decomposition is faster than the flow tube residence time. By 800 K there is essentially no remaining cubane. The dominant product channel is loss of C2H2, delding benzene. Some rearrangement to COT was observed above 650 K, and a small amount of styrene was found at high temperatures. The decomposition lifetimes corresponding to these breakdown curves are given in Table 4.2. 

Figure 4.8 presents the pyrolysis breakdown curves for AEBCB. 

Using a fixed photon energy (21.22 eV), the breakdown curve has been obtained for HF loss from the vinyl fluoride ion and a rate coefficient, k(E), has been derived [211, 784]. 

The decay curves (lifetime distributions) in the microsecond time frame for the formation of (C3HS)+ from the molecular ions of but-l-ene, cis- and frcms-but-2-ene, methylcyclopropane and 2-methylpropene have been determined but the curves could not be described by single rate coefficients. The interpretation put forward was, in effect, that there were two (or more) reacting configurations [20]. Breakdown curves have been reported for butadiyne [210]. 

The decompositions of bromobenzene [717] and chlorobenzene ions [716] have been studied by the special PIPECO experiment using variable source residence times. In the case of chlorobenzene, increasing the residence time from 0.7 to 8.9 ps resulted in a shift (kinetic shift) in the breakdown curves by 0.4 eV. Detailed analysis of the effects of varying residence time provided information on the k(E) vs. E curve in the vicinity of 104—106 s-1. The k(E) vs. E curve obtained differed significantly [by almost an order of magnitude in k(E) at some energies] from the curve reported in the earlier PIPECO study of metastable ions [22], The initial analysis [716] placed the critical energy for chlorine loss at 3.40 0.05 eV, but this has subsequently been revised to 3.19 0.02 eV [717]. The transition state was found to be loose . 

The composition of the blue product was not established with certainty in Fredenhagen s work and Schleede and Wellmann (79) first derived the formula CigMe from crystal-structure measurements. However, further analytical and X-ray investigations by Riidorff and Schulze (66, 67) showed conclusively that the blue compounds contained less alkali metal and had the formula C24Me. This conclusion is supported by Harold s work (32) which show ed that in the isobaric breakdown curve of CgK the first clear break occurs at C24K. This product gave the same X-ray powder pattern as the blue compound studied by Schleede (31). 

If metastable ions are observed in charge exchange experiments, both the lifetime and the internal energy of the reactant are defined as in the analogous PIPECO experiment. The energy at which the intensities of the reactant and fragment ion in the breakdown curve become comparable may be used as a guide as to where to look for metastable ions,... 

Figure 9.4 Corrected JP-10 breakdown curves 1 — JP-10 2 — C3H4 3 — benzene 4 — CPD 5 — C4H1 6 — CrHi (x = 6.8) 7 — CrHio and 8 — unfit residual.

Figure 5. Generalized Voltage Breakdown Curve for Polyethylene Containing High Concentrations of Liquid Peroxide Decomposition Products (acetophenone).

IR spectra, 209-10,213f in polyethylene, voltage breakdown curve, 241,243f Acrylic coatings... 

Quantitative applications of quasiequilibrium theory have eliminated this uncertainty in the average value of , the internal energy, and in the dispersion of . Product spectra for the ion-molecule reaction may be obtained for a fixed collision energy, using, for example, the longitudinal tandem technique and these may be compared with the breakdown curve... 

FfGURE 30 Breakdown curves from energy-resolved tandem mass spectrometry experiments of all four caffeoylquinic acids. The x-axis shows the relative collision energy (one unit corresponds to 0.1 V applied in an ion trap mass spectrometer). The y-axis shows the intensity of the precursor ion at m/z 353. 

FIGURE 6.4 Superimposition of breakdown curves determined for the 1 1 IB7,4 catechin complex when the heated capillary temperature was varied throughout the range 40-240°C in increments of 10°C. 

FIGURE 6.5 Breakdown curves determined for a 1 1 IB934 naringenine-7-O-neohesperi-doside complex with isolation widths for the precursor ion set at 3, 5, 10, and 20 Th. 

The QET was developed simultaneously with the RRKM theory by Rosenstock [11] and used in the mass spectrometry literature to explain breakdown curves whereas the RRKM theory was developed for neutral reaction kinetics, but they ate basically identical. 

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