Showing papers on "Chemical binding published in 1972"

The Carbon Balance of Plants

Abstract: There has been considerable recent interest in the assessment of the en­ ergy allocation of plants (38, 50, 52). It is likely that through a quantitative understanding of how different plants gain and allocate their resources it will be possible to make predictions as to their success in any given physical envi­ ronment in combination with any competitor and predator. We are still far from this reality. However, as a contribution toward this goal, this review seeks to gather the available. information on the various evolutionary strate­ gies which plants have evolved to gain energy and to account for the numer­ ous ways in which this energy is utilized to meet the demands of the environ­ ment, as well as to successfully produce progeny. To date, studies which have considered allocation have generally been at a rather gross level-e.g., reproductive versus nonreproductive (38), roots versus shoots (117), and photosynthetic versus nonphotosynthetic tissue (86). A study by Harper & Ogden (52) has attempted, however, to account in somewhat more detail for the various sources of energy allocation. To account in more detail for energy gain in allocation and for its even­ tual loss through a variety of routes, the approach that will be used here is the capture of carbon by plants and its SUbsequent diversion into various products which perform a multiplicity of functions. Carbon is the vehicle by which organisms store and transfer energy by chemical binding. This device enables the utilization of a large reservoir of physiological and ecological data into a single coherent body. However, it becomes rather clear that the total information required for any given plant simply does not exist. Thus, this review unfortunately can represent only a composite picture of the gen­ realized routes of carbon movement in plants. It does, however, call attention to the continual partitioning of resources and the multiplicity of carbon path­ ways. Emphasis is placed on the modes of capture of carbon. Hopefully, this analysis will stimulate studies which will provide, for a given series of bio­ types, the total information on carbon gain, use, and loss, so that quantitative models can be derived relating these to shortand long-term environmental influences.

Chemical aspects of glass formation in telluride systems

Abstract: The compositional dependence of the electrical activation energy, the optical absorption and the glass transition temperature in typical binary, pseudo-binary and ternary glass forming telluride systems has been measured in an effort to correlate chemical binding with physical properties. A modification of the valency satisfaction model to include chemical ordering effects is required to account for the property singularities observed in the GeTe system at the composition GeTe2. The ordering effects in Te-based alloys containing Ge are further verified by an endothermic disordering reaction in these liquids peaking between 400–475°C depending on composition.

The role of kinetic energy in chemical binding

Abstract: In a preceding paper, we examined the GI wavefunctions of small molecules and found that the nonclassical or exchange kinetic energy, Tx, dominates the changes in energy involved in chemical binding. Here we examine more closely the changes in Tx with internuclear separation and find that ΔTx is large for valence orbitals centered on different atoms because of the large region in which the orbitals are contragradient (i.e., have gradients in obtuse directions). In fact for H2 this contragradience accounts for 93% of the calculated binding energy. In addition, the behavior of Tx and ΔTx can usually be predicted from consideration of the permutational symmetry (Young tableau) involved in the wavefunction. The concepts developed here provide an alternative interpretation of the nature of the chemical bond.

Small-Angle Electron Diffraction by Gases. : An Apparatus with Electron-Counting Device

Abstract: An electron-diffraction unit with a scintillation-counting system is designed and constructed for the purpose of precisely measuring scattered intensities of fast electrons in a small-angle region, 5 mrad–90 mrad By means of a new scanning technique, an accuracy of 0015 mrad is attained The intensities of 42 keV electrons scattered by water molecules are measured with a precision of about 1% in the s-range of 1 to 8A-1 A chemical binding energy of 035±01 au is obtained from the differences between the observed and theoretical intensities based on the independent atom model This is in good agreement with a reported value derived from a thermochemical method

Direct Comparison of Auger Electron Spectroscopy with Appearance Potential Spectroscopy

Abstract: Direct comparison of Auger electron spectroscopy (AES) with appearance potential spectroscopy (APS) has been accomplished. In situ determination of the respective spectra for various surface conditions of an Fe-Cr-Ni alloy has shown that the relative sensitivities of the two techniques are strongly dependent upon the surface condition and that for a given element one technique may indicate an increase with a change in surface condition while the other technique may indicate a decrease. To a first approximation, such effects may be explained in terms of the respective electronic transitions. The results suggest that AES should be employed for elemental and, in some cases, chemical analyses and APS should be reserved for the study of the chemical binding of atoms in surfaces.

On the possibility of an organic magnet

Abstract: The conditions needed to produce an organic ring-shaped molecule exhibiting a persistent magnetization are calculated from quantum and chemical considerations. Using a simplified one-particle operator model and known chemical binding energies it is concluded (a) that such a molecule would need to be very large (circa) 100 A diameter) to be ‘stable’, (b) that synthesis would probably need to take place in a pre-existing strong magnetic field.

Physical aspects of the crystalline electric field (CEF)

Abstract: The present article describes some important effects that the crystalline electric field (CEF) produces in solids and particularly in metals. Emphasis is laid on a description in simple physical terms rather than on detailed mathematical analysis. We first give an outline of the way the CEF acts as a perturbation on the spectroscopic state of the free ion and we discuss briefly the limits of the model including its relation to chemical binding. We then describe the consequences of the CEF interaction including the information that may be obtained from experiment. We discuss the following topics: magnetic moment, susceptibility, magnetic anisotropy, Schottky specific heat, electron paramagnetic resonance, hypertine structure, magnetic form factor, neutron scattering from CEF levels, magnetic excitons and light scattering. In particular we emphasize the relation between CEF effects and neutron scattering because the availability of strong thermal neutron sources will certainly stimulate this field of research.