Relative Potential Energies Research Articles

Conformational statistics of poly(dimethylsiloxane). 1. Probability distribution of rotational isomers from molecular dynamics simulations

The probability distribution of isomeric conformations in poly(dimethylsi1oxane) has been investigated both by conformational energy considerations and by molecular dynamics simulations. A comparatively smooth distribution of isomeric states is obtained from both approaches. The molecular dynamics trajectory of a simulated dimethylsiloxane oligomer of eight units is used as a reliable and realistic tool to estimate the probability of occurrence for various rotational isomeric states. Conformations involving bonds in the gauche state produce attractive intramolecular potentials through suitable spatial arrangement of close neighbors, which is contradictory to the unfavorable interactions attributed to them in the model described by Flory, Crescenzi, and Mark. The relative potential energies of the various conformational states are obtained from the probability of those conformations occurring in a molecular dynamics simulation.

Basis Set Dependency of Energy Components in Hartree-Fock MO Theories. II. Conservability of Virial Ratio between Different Conformations

Abstract The authors examined 22 different basis sets in order to determine exactly how they reproduce the relative kinetic and potential energies. In an attempt to find the calculation error of such energy components, the virial relationship has been used between two conformations in which all bond lengths are optimized with respect to the total energy: i.e., the relationship, ΔV=−2ΔT, where ΔV and ΔT are the differences in the potential and kinetic energies. The degree of error was compared in terms of the relative virial error ((ΔE+ΔT)⁄ΔE) to the difference in the total energies (ΔE). STO-NG was found to give a large amount of casual error, up to 500% to ΔE. Such an error could be dramatically improved by using a split-valence method. It should be noted that 4-31G and 6-31G methods resulted in a small amount of error and that the inclusion of polarization functions does not always improve the amount of error.

The Mechanism of the Reaction of 3,5-Dinitrobenzonitrile with Sodium Methoxide in Methanol

Abstract The reaction of 3,5-dinitrobenzonitrile in a methanolic solution containing a low sodium-methoxide concentration has been reinvestigated. The final product has been found to be methoxy(3,5-dinitrophenyl)methanimine, which is produced by a catalytic reaction. The reaction mechanism has been presented for the formation of the Meisenheimer complexes and the final product in the reaction system. The rate and thermodynamic stabilities for their formation have been discussed on the basis of the LUMO coefficients of 3,5-dinitrobenzonitrile and from the relative potential energies of their formation respectively, considering also the solvent effects.

Electron Impact Mass Spectrometric Study of Vacuum-Deposited Nickel and Gold Films on Silicon Substrates

An experimental electron impact ionization source is used with a mass spectrometer to determine the presence of various neutral atoms and molecules on nickel and gold films vacuum-deposited on silicon substrates. The mass peaks can be classified into three groups: monoenergetic, polyenergetic and combined. The groups are characterized by the peak shapes which depend on the ion sources. The major surface contaminants found on all samples are F, Na, Cl, K, CO and CO2. The sources of some ions and their relative potential energies at the point of formation are determined by calculating the appearance potentials, from the mass peak shapes which are characteristic of this method, and by comparing these potentials with known appearance potentials.

Scission-point model of nuclear fission based on deformed-shell effects

A static model of nuclear fission is proposed based on the assumption of statistical equilibrium among collective degrees of freedom at the scission point. The relative probabilities of formation of complementary fission fragment pairs are determined from the relative potential energies of a system of two nearly touching. coaxial spheroids with quadrupole deformations. The total potential energy of the system at the scission point is calculated as the sum of liquid-drop and shell- and pairing-correction terms for each spheroid, and Coulomb and nuclear potential terms describing the interaction between them. The fissioning system at the scission point is characterized by three parameters---the distance between the tips of the spheroids ($d$), the intrinsic excitation energy of the fragments (${\ensuremath{\tau}}_{\mathrm{int}}$), and a collective temperature (${T}_{\mathrm{coll}}$). No attempt is made to adjust these parameters to give optimum fits to experimental data, but rather, a single choice of values for $d$, ${\ensuremath{\tau}}_{\mathrm{int}}$ and ${T}_{\mathrm{coll}}$ is used in the calculations for all fissioning systems. The general trends of the distributions of mass, nuclear charge, and kinetic energy in the fission of a wide range of nuclides from Po to Fm are well reproduced in the calculations. The major influence of the deformed-shell corrections for neutrons is indicated and provides a convenient framework for the interpretation of observed trends in the data and for the prediction of new results. The scission-point configurations derived from the model provide an interpretation of the saw-tooth neutron emission curve as well as previously unexplained observations on the variation of $\stackrel{-}{\mathrm{TKE}}$ for isotopes of U, Pu, Cm, and Cf; structure in the width of total kinetic energy release as a function of fragment mass ratio; and a difference in threshold energies for symmetric and asymmetric mass splits in the fission of Ra and Ac isotopes. In spite of a number of recognized simplifications in the model, quantitative fits to the data are generally within expected errors of the shell corrections determined by the Strutinski prescription.NUCLEAR REACTIONS, FISSION Po, Ra, U, Cm, Cf, Fm; calculated $A$, $Z$, and KE distribution of fragments. Liquid-drop model. Deformed-shell corrections. Strutinski prescription. Asymmetric and symmetric fission.