TL;DR: ABSOLUTE values of the electron affinity, E, of organic molecules have not been determined experimentally except in a few cases, and in most of these the uncertainty is several tenths of an electron volt or even more as discussed by the authors.
Abstract: ABSOLUTE values of the electron affinity, E, of organic molecules have not been determined experimentally except in a few cases1,2, and in most of these the uncertainty is several tenths of an electron volt or even more. Some theoretical values have also been calculated3. Since the electron affinity is a fundamental molecular property and also is4 of considerable importance to modern biology it is desirable that more and better values be found.
TL;DR: The absolute electron affinities of pi charge transfer complex acceptors have been examined and the "best" values have been chosen as discussed by the authors, and the magnetron results for anthraquinone and benzoquinone are not in agreement with the half-wave reduction potential data.
Abstract: The absolute electron affinities of pi charge transfer complex acceptors have been examined and the ’’best’’ values have been chosen. All of the results obtained by the magnetron method, including the estimates for hexafluorobenzene and tetracyanoethylene, were accepted. However, the magnetron results for anthraquinone and benzoquinone are not in agreement with charge transfer complex and half‐wave reduction potential data. The half‐wave reduction potential data and the charge transfer complex data for all of the other acceptors for which absolute electron affinities are available were found to be consistent with the usual correlation equations and their associated assumptions. The parameters from these correlations have been used to calculate the absolute electron affinities for about 150 acceptors.
01 Jan 2009
TL;DR: In this article, the formulation of totally formaldehydefree adhesives based on tannins obtained from some lignocellulosic forest and/or industrial wastes was considered.
Abstract: 11 Nowadays most industrial wood products are manufactured with thermosetting synthetic resins being the most used those based on formaldehyde. However, environmental and health considerations are leading to more severe standards according to the maximum permissible formaldehyde emissions from wood-based boards. This joined with the increasing costs of petroleum-based synthetic resins has intensified the search for alternative resins based on natural and environmentally friendly materials for wood adhesives preparation. Therefore, there are proposals of different types of formaldehyde-free resins, based on condensed tannins, lignin, vegetable oils, proteins and soy flour. Tannins extracted from lignocellulosic materials have been employed in the formulation of adhesives in combination with synthetic resins based on formaldehyde or using formaldehyde as hardener, with satisfactory results in the preparation of wood boards. However, the possible presence of free formaldehyde in the finished boards, limits its commercial attractive. In this work the formulation of totally formaldehydefree adhesives based on tannins obtained from some lignocellulosic forest and/or industrial wastes was considered. This can be achieved by using alternative hardener compounds such as glyoxal, hexamethylenetetramine and tris(hydroxymethyl)nitromethane. Chestnut (Castanea sativa) shell and bur and eucalyptus (Eucalyptus globulus) bark are lignocellulosic wastes produced in significant quantities by food and forest (pulp and wood boards) Galician industries, respectively. Its availability, its renewable character and chemical nature have been the reasons for proposing a new application oriented to the development of high added-value products as an alternative to their actual use for energy production in the industries that generate them. The study was performed in various stages: study of extraction conditions and characterization of the tannin extracts obtained, adhesives formulation and their physicochemical characterization and particle board manufacture with selected adhesives and their quality analysis. The extraction conditions study began with a preliminary study applied to chestnut shell and eucalyptus bark in which it was concluded that chestnut shell extracts showed better properties for wood board adhesives formulation than eucalyptus bark due to higher Stiasny number values and total phenol content, together with substantially
TL;DR: In this paper, the authors explored the recent work on the lifetimes of metastable molecular negative ions and a wider understanding is endeavored, including the mechanism by which an electron is trapped in a potential well arising from the interaction between the incoming electron and the neutral molecule.
Abstract: Publisher Summary This chapter deals with the lifetimes of metastable negative ions. This chapter explores the recent work on the lifetimes of metastable molecular negative ions are synthesized and a wider understanding is endeavored. A negative-ion resonance (NIR) is formed when the incident electron attaches itself to a neutral atom or molecule for times longer than the electrons normal transit time through the molecule and they are viewed as nonstationary states of the electron-atom (molecule) system. Basically, four types of NIRs can be distinguished, depending on the mechanism by which the electron is trapped: shape or single-particle resonances, core-excited resonances core-excited resonances, and nuclear-excited Feshbach resonances. Finally, shape resonances result when the incident electron is trapped in a potential well arising from the interaction between the incoming electron and the neutral molecule in its electronic ground state.
TL;DR: In this article, bound and excited negative ion states of para-benzoquinone (PBQ) were studied from experiments involving collisions of electrons and cesium beams with PBQ.
Abstract: Bound and excited negative ion states of para‐benzoquinone (PBQ) are studied from experiments involving collisions of electrons and cesium beams with PBQ. The electron affinity of PBQ was measured to be 1.89+0.2−0.3 eV using the cesium collisional ionization technique. PBQ−(C6H4O−2) was the dominant negative ion observed following collisions of cesium beams with PBQ. Direct electron attachment to PBQ produced the fragment ions C5H4O−, C5H3O−, C4O2H−2, C2HO−, and C2H− as well as the parent C6H4O−2 ion. Our observations showed that the cross section for producing the metastable parent negative ion, C6H4O−2, peaks at 1.40±0.1 eV which is in disagreement with a previous value of 2.1 eV. Attachment of thermal electrons to PBQ at low pressure (<10−4 mm Hg) was not observed. Compound negative ion states were observed to peak at 0.70, 1.35, and 1.90 eV using the SF6 scavenger technique. The energies of these compound states agree qualitatively with the energies if the manifold of unfilled π* orbitals. The long‐li...