Further correlations between fragment ion intensity and critical energy. Unimolecular covalent bond fragmentation

A correlation of fragment ion intensity with critical energy found in the collisional activation spectra of [C₄Ph]⁺˙ ions produced by electron impact can also be found in the unimolecular mass-analysed ion kinetic energy spectra of these ions. The P(E) functions of the unimolecular and collisionally activated ions should differ not only in width but also in structure and therefore, the hypothesis that P(E) functions do not have an important effect on these correlations is tested successfully.     

THE ENERGY ASPECT OF THE RECIPROCAL INTERACTIONS OF PAIRS OF TWO DIFFERENT VIBRATION MODES OF A CLAMPED ANNULAR PLATE

The standardized mutual active and reactive sound power of a clamped plate, representing the energy aspect of the reciprocal interactions of two different in vacuo modes, has been computed. It was assumed that the vibrations are axisymmetric, elastic and time harmonic, the plate's transverse deflection is small as compared with the plate's size, and that the vibration velocity is small as compared with the acoustic wavenumber generated. The Kirchhoff-Love theory of a perfectly elastic plate was used. The integral formulae for the mutual sound power were transformed into their Hankel representations which made possible their subsequent computation. A closed path integral was used to express the integral in its Hankel representation to compute the mutual active sound power. The asymptotic stationary phase method was used to compute the two magnitudes, i.e., the mutual active and reactive sound power. The results obtained are the asymptotic formulae valid for the acoustically fast waves. The oscillating as well as the non-oscillating terms have been identified in the formulae to make possible their further separate analysis. The availability of the asymptotic formulae makes possible some fast numerical computations of the mutual sound power. Moreover, the formulae presented herein, together with those for the individual modes known from the literature, make a complete basis for further computations of the total sound power of the plate's damped and forced vibrations in fluid.     

History of Polymer Education-USA

Prior to 1940 there was little or no education directed toward polymer chemistry. With the contributions of Carothers and others that transformed the practice of polymers into a science-and the leadership of Herman Mark and others in formal graduate and postgraduate education-polymer education took root but rapid expansion and general acceptance by more traditionally oriented academic institutions was slowed by many barriers. Only since 1974 has there been a concerted effort to include education in the basic concepts of polymer chemistry into the undergraduate curriculum. Emphasis is on the development of polymer education in the United States.     

A non-empirical molecular orbital study on loewenstein''s rule and zeolite composition

The role of the “aluminum avoidance rule” in zeolite frameworks and its relation to the electronic structure and stability of various structural units of alumosilicates were studied by non-empirical SCF—MO techniques. Al—O—Al-type linkages are unstable according to the calculations. The presence of cations in the neighbourhood of T₁—O—T₂ bridges (T₁, T₂ = Si or Al) is the least stabilizing when T₁ = T₂ = Al.     

Survey of reaction types in low-energy colliosional activation of protonated methyl alkyl ketones

In contrast to high-energy collisions, where simple cleavages are commoner, rearrangements typically account for 96–100% of products in low-energy collisions of the [M + 1]⁺ ions of aliphatic methyl ketones. Rules for predicting low-energy helium collsional-activated decomposition (CAD) spectra of the ketones are based on proton affinities of fragments formed by simple rearrangements. The commonest reaction is equivalent to the energetically improbable four-center 1,3-H or 1,3-R shift; other rearrangements equivalent to processes with five-, six-, or seven-center activated complexes are less important. In larger ions, loss of water followed by loss of alkene dominates. O-Protonated enol forms either lose water to give a carbonium ion that rearranges to forms capable of losing olefin fragments, or rearranges to an intermediate in the formation of acetyl ion and an alkane. O-Protonated keto forms rearrange to alkanes and protonated smaller carbonyl compounds. The ion kinetic energies necessary to produce several intense daughter ions at threshold establish the order of sequential fragmentations. When helium is the collisional gas and the ion energy is 30 eV in the laboratory frame (the maximum value studies), the ion energy is only 0.8–1.9 eV in the center-of-mass frame depending on its size. Only a fraction of this kinetic energy is converted to internal energy, so that onsets of reaction channels differing by several tenths of an electron-volt are easily studied. Some isomers of methyl ketones can be easily distinguished by He-CAD spectra of their [M + 1]⁺ ions.