Fragment species

The LD spectrum of the tridecapeptlde neurotensin (Figure 4), shows several differences. Here fragmentation results almost exclusively from small neutral losses. A protonated molecular ion is still one of the major ions observed (m/z = 1673) and some cationized (K+) fragment species are apparent as well as a small amount of cationized molecular ion (<5%). Resolution has begun to be degraded to some extent, partially due to the decrease in overall ion signal which necessitates transformation of fewer data points to maximize signal to noise ratio. 

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry MALDI-TOF appears the newest technique particularly suitable for the study of oligomers and dendrimers because, under appropriate conditions, the parent peak is obtained uncontaminated by fragmentation species. However, in some cases supramolecular clusters have been observed which could be misinterpre-tated as dimers and higher multiplets [13]. The molecular weight range available reaches 50,000 D with a potential resolution between 0.01 and 0.05%. 

Electrons may interact with molecules and cause them to dissociate. These processes are collectively termed EID. EID proceeds via two main pathways. The first arises by the attachment of an electron, where it resides in one of the lowest unoccupied ground state molecular orbitals and forms a negative ion. This state is usually short lived. In many molecules, these temporary negative ion states are dissociative, and produce a neutral and negatively charged fragment species. 

The yields were calculated from the abundances of the fragment species measimed in the low-pressure decay-induced dissociation of the isomeric monotritiated propanes, assuming a statistical distribution of T among the dissociation products. Cacace et al. (1967). 

It should be clear from the discussion of Section 2 that all of these clusters can be unstable with respect to cluster degradation in the presence of Lewis bases with the formation of saturated fragment species (see Boron Hydrides and Polynuclear Organometallic Cluster Complexes). Thus, in the presence of an excess of phosphine, the reaction of [HFe3(CO)9(/u-H)2BH] changes from that shown in equation (10) to that shown in equation (12). The mononuclear boron and iron products demonstrate that both transition metal and main group element vertices are removed by base and the cluster is degraded. ... 

The ionization of an organic molecule is the basic principle of mass spectroscopy however, it should be recognized that mass spectroscopy of a simple molecule such as ethane generally shows multiple ions, covering the fragmented species to partially polymerized species, which indicates that the dissociation of the molecule and some extent of polymerization of fragmented species occurred in the mass spectrometer. The presence of the DG (cathode glow) in DC cathodic polymerization implies that the formation of chemically reactive species via ionization, as depicted by Eq. (4.1), is a very unlikely primary event under the conditions of LCVD. 

The effectiveness of chemical etching is largely dependent on the volatility of fragmented species. For instance, oxygen plasma is an effective etching gas for most... 

The plotting deposition rates of different monomers with different feed rates in Normalized DR) versus W FM)cI FM)t coordinates would provide the most objective comparison of their tendencies with regard to deposition in CAT LCVD. In LCVD, it is very important that the polymerization (material formation) is atomic rather than molecular processes, implying that the depositing entities are fragmented species of the original monomer molecule. Therefore, the deposition rate in LPCAT polymerization is determined largely by the type of atoms contained in the monomer structure rather than by molecular structures. 

Many rearrangements have been invoked to explain the fragmentation pattern of molecular ions22 (It should be remembered that the fragmenting species are radical cations. Their radical functionality may open to them reaction paths which are not available to simple carbocations). Only a few illustrative examples of well-established alkyl and aryl shifts are given here. The mass spectrum of camphor displays the base peak at m/e 95, corresponding to the loss of ketene and a methyl radical. As shown... 

Altogether, 62 >S02 molecules were studied, not counting the atom and small fragment species needed to calculate certain thermodynamic quantities. The calculated results are presented in Tables 1-18 and Figures 1-60. Generally, the tables fall into the following categories. 

When the fragment species is an ion, formed either from the dissociation of a parent ion or ionized after the dissociation event, the kinetic energy release distribution (KERD) can be measured with much greater efficiency. Suppose that an electric field... 

Fig. 1. Results of polymerase slippage in 1-, 2-, and 3-bp repeats. (A) shows the number of fragment species generated from a sample homozygous for a 26-bp pair poly-A repeat. The generation of as many as seven different detectable fragments after both PCR optimization and primer pig-tailing is common. The number of species generated by polymerase slippage in the 2-bp repeat (B) and a 3-bp repeat (C) are greatly reduced.

Fig. 2. The effects of pig-tailing the amplification primers to maximize the Taq adenosine addition. The addition of an adenosine to the 3 end of amplicons that is not matched in the amplification template is shown to greatly increase the number of observed fragment species even after the optimization of PCR conditions in a sample heterozygous for a 2-bp repeat (A). The addition of the GTTTCT pig-tail to the 5 end of the reverse primer greatly increases the affinity of this addition reducing the number of observed fragments (B). Note the increase in overall fragment size of seven base pairs, which represents the 6-bp primer addition and the added adenosine.

ROOH -I- R ), as well as other fragment species (H2O, H2, H2O2). 

This model has been tested primarily on polymer systems (a more detailed treatment will be presented in a publication in preparation) but appears to explain to a great extent the observed features of FE, in particular, the time dependence of EE and PIE. In terms of applications involving adhesive failure, such a model would be useful to relate the measured FE characteristics to fracture phenomena of interest i.e., the fragment species, density of trapped electrons, initial concentrations (before decay) and their rate of production all should be closely related to processes occurring at the crack tip. Although the FE model and characteristics outlined above have been observed in a limited number of situations, there appears to be evidence for considerable generality. 

---