Search results for "fragmentation"

Solution for the fragment-size distribution in a crack-branching model of fragmentation

2007

It is well established that rapidly propagating cracks in brittle material are unstable such that they generate side branches. It is also known that cracks are attracted by free surfaces, which means that they attract each other. This information is used here to formulate a generic model of fragmentation in which the small-size part of the fragment-size distribution results from merged crack branches in the damage zones along the paths of the propagating cracks. This model is solved under rather general assumptions for the fragment-size distribution. The model leads to a generic distribution S(-gamma) exp(-S/S(0)) for fragment sizes S, where gamma = 2d-1/d with d the Euclidean dimension, an…

Signature of cluster isomers in time-resolved photodissociation experiments

2004

Abstract The unrecognized presence of structure isomers in mass-selected cluster ensembles may obstruct investigations of the systems’ intrinsic properties, since isomers differ not only in geometry, but also in other important properties. By the same token isomers are very interesting objects in the detailed study of atomic clusters. In the present work, different scenarios of isomeric coexistence are presented. They vary in the relative values of the interconversion barrier and the dissociation energies. For some idealized cases the possibility of a distinction of isomers by photodissociation experiments is discussed. In favorable situations isomeric structures may even be selected.

Characterization of some isomeric benzophenones by their mass spectra

1979

Benzophenones have been described to undergo characteristic α-cleavage and rearrangement processes upon mass spectrometric fragmentation. Recently two series of new and isomeric benzophenones have been prepared from phenylbenzoates by Fries rearrangement or directly by Friedel Crafts acylation. It is shown that the above mentioned diagnostic fragmentation processes can be used to characterize the resulting isomeric ortho or para hydroxy and ortho or para methoxy benzophenones unambigously.

Untersuchungen von Polymeren im Massenspektrometer. I. Fragmentierungsreaktionen von oligomeren β-Alaninen

1973

Beim Abbau von Poly-β-alaninen entstehen unter milden Pyrolysebedingungen oligomere Carbonsaureamide. Die Fragmentierungsreaktionen derartiger Pyrolysebruchstucke werden an dimeren bis tetrameren β-Lactamen untersucht. Als Hauptfragmentierungsreaktionen werden nach Ionisation an einem der Heteroatome αN-, Keten-, αO-, und βO-Spaltung mit MCLAFFERTY-Umlagerung gefunden. The degradation of poly-β-alanines under mild pyrolytical conditions yields oligomeric amids. Dimeric, trimeric and tetrameric β-lactames were used to study the fragmentation reactions of those degradation products. After ionisation at one of the hetero atoms αN-, keten-, αO- and βO-cleavage (with MCLAFFERTY-rearrangement) we…

Metastable ion studies. 4—mass spectral fragmentation and isomerization in the esters of chlorinated propenoic acids

1983

Metastable peaks have been used to study the fragmentation pathways of the methyl and trideuteriomethyl chloropropenoates and chloromethyl propenoate. The molecular ion peaks of the unsaturated esters are more intense than those of the saturated esters, α-Cleavage, [MOCH3]+, produces the base peak in almost all compounds, the relative abundances of the additional peaks being low for chloromethyl propenoate. The losses of H2O, CH3. and COOH. indicate the isomerization of some ionized chloro esters to the chlorinated 2-butenoic acid molecular ions. An intense loss of H2O observed for methyl 2-chloropropenoate indicates its most facile isomerization, [ester]+˙ → [acid]+˙, whereas the isomeriza…

Untersuchungen von polymeren im massenspektrometer, 5. Fragmentierungsreaktionen oligomerer oxy- und thio-1,4-phenylene

1975

Als Modellverbindungen zur Differenzierung von thermischen und elektronenstosinduzierten Abbaureaktionen von entsprechenden Polymeren im Massenspektrometer wurden die Fragmentierungsreaktionen oligomerer 1,4-Phenylene mit Sauerstoff-, Schwefel- und Disulfidbrucken sowie eine Reihe alternierender Co-oligomersysteme untersucht. Bei verringerter Ionisationsenergie (15 eV) treten in den Massenspektren aller unzersetzt fluchtigen Oligomeren die Molekulionen als intensivste Peaks auf, so das–bei strukturell gleichen Polymeren–eine eindeutige Identifizierung von thermischen Abbauprodukten erwartet werden kann. In Abhangigkeit von den Bruckenatomen werden charakteristische Unterschiede in den Inten…

1978

The mass spectra of cycloolefins (C12xH22x), cycloalkanes (C12xH24x), and unbranched alkanes are compared. The most prominent fragmentation series are CnH2(n–p)−1⊕, CnH2n − 1⊕, and CnH2n+1⊕, respectively. The intensity of the molecular ion peak decreases in the order given.

Generation of monosubstituted o-benzynes from polymeric reagents via heterolytic fragmentations

1984

Abstract Generation of four 4-substituted o-benzynes by heterolytic — fragmentation reactions is demonstrated.

Massenspektrometrische Untersuchungen an 4-[(2-Amino-ethylmercapto)-methyl]-imidazolen

1981

Es wurden 7 unterschiedlich substituierte 4-[(2-Amino-ethylmercapto)-methyl]-imidazole unter den Bedingungen der Elektronenstosionisation massenspektrometrisch untersucht. Unter Berucksichtigung der charakteristischen Verhaltensweisen dieser Stoffgruppe wird ein Schema der Hauptfragmentierungswege vorgeschlagen. Mass Spectrometry of 4-[(2-Aminoethylthiomethyl]imidazoles 7 substituted 4-[(2-aminoethylthio)methyl]imidazoles were investigated by electron impact mass spectrometry. The main fragmentation paths are described and the characteristic fragments are tabulated.

An ab initio and DFT study of the fragmentation and isomerisation of MeP(O)(OMe)+

2004

The fragmentation behaviour of the ion MeP(O)OMe+ has been investigated using quantum mechanical calculations at the B3LYP and MP2 levels to support experiments made with an Ion Trap Mass Spectrometer. Two mechanisms for the loss of CH2O are found, one involving a 1,3-H migration to phosphorus and the other a 1,2-methyl migration to give P(OMe)2+ followed by a 1,3-H migration. In each case an ion-dipole complex is formed that rapidly dissociates to yield CH2O. The relative importance of each route has been previously determined experimentally via isotopic labelling experiments, and the theoretical results are found to be consistent with these experimental results. The mechanisms suggested i…