We prove that for any process which admits a parton-model interpretation, the naive parton model can be modified to include the effects of QCD interactions to all orders in perturbation theory. This requires that the mass singularities in quark and gluon inclusive cross sections factor into universal functions which renormalize the naive parton model distribution and decay functions. We prove that this factorization takes place for all leading and non-leading logs and thus check consistency of the parton model to all orders in perturbation theory. 相似文献
We have investigated possible relationships between four crystal properties: experimental densities and computed intrinsic molecular volumes, packing coefficients and amounts of free space per molecule in the crystal lattices. Our focus was upon C-, H-, N-, O-containing explosive compounds. The objectives were to gain some insight into how densities might be increased, to improve detonation performance, and the amounts of free space per molecule decreased, to counter one of the factors promoting undesired sensitivity to accidental stimuli. The issue of molecular planarity was also examined. The best correlation found between the four properties is perhaps a surprising one: The free space per molecule increases as the molecules are bigger. On the other hand, some relationships that seem to be intuitively reasonable turn out to be quite weak. The principal positive conclusions are that it is desirable for explosive compounds to be composed of molecules that are small and preferably planar.
In recent years, there has been considerable interest in predicting the crystal densities of both molecular and ionic energetic compounds using the computed volumes Vm of the isolated gas phase molecules or ions. The surfaces enclosing the volumes are taken to be the 0.001 au (electrons/bohr3) contours of the molecules’ and ions’ electronic densities. For molecular solids, it is known that the ratio M/Vm (M = molecular mass) gives densities that are overall reasonably good, although they can be markedly improved by introduction of an electrostatic interaction correction term. For ionic solids, the subject of this paper, the ratio M/Vm (M = formula unit mass) is not nearly as effective; Vm tends to be significantly larger than the effective volumes of the ions in the crystal, leading to underestimated densities, with an average absolute error of 0.089 g/cm3. The correction term that improves molecular crystal densities is not applicable in the case of ionic solids; however we show, for a database of 25 compounds plus five test cases, that an average absolute error of 0.033 g/cm3 can be achieved by combining M/Vm with terms involving the average positive and negative potentials and areas on the cationic and anionic surfaces. The root-mean-square error is 0.040 g/cm3. 相似文献
ABSTRACTWe have investigated the relevance for ionic explosive sensitivity of three factors that have been demonstrated to be related to the sensitivities of molecular explosives. These are (1) the maximum available heat of detonation, (2) the amount of free space per molecule (or per formula unit) in the crystal lattice and (3) specific features of the electrostatic potential on the molecular or ionic surface. We find that for ionic explosives, just as for molecular ones, there is an overall tendency for impact sensitivity to increase as the maximum detonation heat release is greater. This means that the usual emphasis upon designing explosives with large heats of detonation needs to be tempered somewhat. We also show that a moderate detonation heat release does not preclude a high level of detonation performance for ionic explosives, as was already demonstrated for molecular ones. Relating the free space per formula unit to sensitivity may require a modified procedure for ionic explosives; this will continue to be investigated. Finally, an encouraging start has been made in linking impact sensitivities to the electrostatic potentials on ionic surfaces, although limited so far to ammonium salts. 相似文献
In order to test the validity of approximating the effects of various atomic inner subshells by means of point charges at the nuclei, the electron repulsion and exchange integrals involving these inner electrons and valence electrons were computed for a series of atoms. The point-charge approximation was found to be very poor for the 3s, and 3p subshells of the first-row transition elements. 相似文献
Summary We have investigated some possible initial steps in the unimolecular thermal decompositions of 1,3-diazacyclobutane and its 1,3-dinitramine derivative, the latter being selected as the simplest example of a symmetric cyclic nitramine. Vibrational analyses were used to identify normal modes that, in the extreme limits, would correspond to bond rupture and molecular decomposition. The energy requirements for ring fragmentation and N-N bond-breaking were computed at the MP4/6-31G level, using SCF 3-21G optimized structures. It was concluded that ring-fragmentation is a probable initiating step in the decomposition of the unsubstituted molecule, and that it is roughly competitive with N-N bond scission for the dinitramine. The nitronitrite rearrangement is predicted, on the basis of SCF calculations, to be less likely than either of the other two processes. It is proposed that N-N bond-breaking may be of primary importance for nitramine stability, but that energetic performance may be determined more by decomposition pathways having energy barriers. 相似文献
A computational analysis of the electrostatic potentials of eight halogenated dibenzo-p-dioxins has been carried out at theab initio SCF STO-5G level. It focuses upon the relationships between these potentials and the biological activities of the molecules, including toxicity, aryl hydrocarbon hydroxylase induction and receptor binding. In general, regions of negative potential are found to be associated with the oxygens and with the halogen substituents. Biological activity appears to be related to the presence of an optimum range of negative potentials above the lateral portions of the molecules in conjunction with a weakening of those near the oxygens. 相似文献
A group of eight nitrofluoromethanes has been studied by the ab initio SCF GAUSSIAN 82 computational procedure. All structures were optimized at the 3-21G level and then used to compute bond orders, as measures of relative bond strengths, and electrostatic potentials, as guides to the molecular charge distributions. The C-F bonds were found to be strengthened by the presence of other fluorines or nitro groups; this is attributed to inductive electron withdrawal by these other substituents, which leads to significant double-bond character in the C-F bond, through resonance back-donation by the fluorine. This simultaneously weakens or even eliminates the negative electrostatic potential normally associated with the fluorine. The interesting observation that there are marked differences between the strengths of the two N-O bonds in some nitro groups can be quantitatively related to the environment of each oxygen. The C-NO2 bond strengths are relatively insensitive to the presence of other-NO2or-F substituents. However, CHF(NO2)2 is found to be significantly more stable than CH(NO2)3, presumably because the crowding of three -NO2 groups together on the same carbon is partially relieved. 相似文献
It is shown that the electronic charge density of a ground-state atom decreases monotonically as a function of radial distance from the nucleus, contrary to the widespread belief that the shell structure is reflected by relative maxima in the density. Any proposed relationship between chemical bonding and the maxima in the radial density functions of atoms should therefore be regarded with caution. It is proven that the electrostatic potential of an atom must be monotonically decreasing. The changes in charge distribution upon molecule formation are also discussed. 相似文献