Engineering topics

Wilson, S.

Publications and source records attributed to Wilson, S..

28 records · Page 2

NASA NTRS1980

Theoretical studies of the HeCN/+/ and NeCN/+/ molecular ions

Self-consistent field calculations are presented for HeCN(+) using several basis sets; calculations for HeH(+) with the same basis sets are given for comparison. These predict that HeCN(+) is stable with a He-CN(+) dissociation energy between 1.5 and 2.0 eV. The binding is found to be mainly electrostatic in nature. Rotation and hyperfine spectral constants are predicted. Similar calculations indicate that the isocyanide HeCN(+) is not stable. Preliminary calculations on NeCN(+) indicate that it is as stable as HeCN(+). The possibility of observing noble gas molecular ions in laboratory experiments and in interstellar space is discussed.

Wilson, S.↗

NASA NTRS1980

The use of an active coded aperture for improved directional measurements in high energy gamma-ray astronomy

The coded aperture, a refinement of the scatter-hole camera, offers a method for the improved measurement of gamma-ray direction in gamma-ray astronomy. Two prototype coded apertures have been built and tested. The more recent of these has 128 active elements of the heavy scintillator BGO. Results of tests for gamma-rays in the range 50-500 MeV are reported and future application in space discussed.

Johansson, A.↗

NASA NTRS1978

Theoretical study of HSiO/+/ and HOSi/+/

Results are reported for quantum-mechanical studies of the ions HSiO(+) and HOSi(+). The equilibrium geometries, rotation constants, and relative stabilities of these ions are determined using the matrix Hartree-Fock model with a basis set of Slater exponential functions. Optimum bond lengths are calculated, and an empirical correction to the computed bond lengths is introduced. The isomer HOSi(+) is found to be more stable than HSiO(+). A frequency of 35.77 GHz is obtained for the J = 1-0 transition of HOSi(+) by assuming that the vibration-rotation interaction constants for this isomer are the same as those for HCP.

Wilson, S.↗

NASA NTRS1978

Theoretical study of the thioformyl ion

The equilibrium structure of the thioformyl ion has been determined from an ab initio matrix Hartree-Fock calculation, and an estimated rotation constant has been derived. A rotation constant of 21.7 GHz is obtained for HCS(+); the corresponding constant for DCS(+) is 18.3 GHz. If the vibration-rotation interaction constants for HCS(+) are assumed to be the same as those for HCP, then the rotation constant is 21.6 GHz, while the vibration-rotation constants of DCP give a rotation constant of 18.3 GHz for DCS(+).

Wilson, S.↗

NASA NTRS1978

Theoretical study of isocyanoacetylene and the isocyanoethynyl radical

Quantum mechanical calculations, using the matrix Hartree-Fock model, have been performed to obtain estimates of the rotation constants of the isocyanoacetylene molecule and the isocyanoethynyl radical which may be detectable in space. A rotation constant of 5076 MHz is calculated for HC2NC, while for the radical C2NC the value 5458 MHz is obtained.

Wilson, S.↗

NASA NTRS1977

Diagrammatic perturbation theory applied to the ground state of the water molecule

The diagrammatic many-body perturbation theory is applied to the ground state of the water molecule within the algebraic approximation. Using four different basis sets, the total energy, the equilibrium OH bond length, and the equilibrium HOH bond angle are examined. The latter is found to be a particularly sensitive test of the convergence of perturbation expansions. Certain third-order results, which incorporate all two-, three-, and four-body effects, show evidence of good convergence properties.

Silver, D. M.↗

NASA NTRS1977

On the representation matrices of the spin permutation group

A method is presented for the determination of the representation matrices of the spin permutation group (symmetric group), a detailed knowledge of these matrices being required in the study of the electronic structure of atoms and molecules. The method is characterized by the use of two different coupling schemes. Unlike the Yamanouchi spin algebraic scheme, the method is not recursive. The matrices for the fundamental transpositions can be written down directly in one of the two bases. The method results in a computationally significant reduction in the number of matrix elements that have to be stored when compared with, say, the standard Young tableaux group theoretical approach.

Wilson, S.↗

NASA NTRS1977

Diagrammatic perturbation theory - The ground state of the carbon monosulfide molecule

Diagrammatic many-body perturbation theory is employed in a study of the ground state of the carbon monosulfide molecule for bond lengths close to the equilibrium value. The calculations are complete through third order in the energy within the algebraic approximation. Two different zero-order Hamiltonians are considered, and all two-, three-, and four-body terms are determined for the corresponding perturbation expansions. Many-body effects are found to be very important. Pade approximants to the energy expansion are constructed, and upper bounds evaluated. Almost 53 percent of the estimated correlation energy is recovered. The variation of components of the correlation energy with nuclear separation is investigated. Spectroscopic constants are also calculated.

Wilson, S.↗

NASA NTRS1977

Diagrammatic perturbation theory - N2 X1 Sigma/plus/g

The diagrammatic many-body perturbation theory is used to calculate the correlation energy of the nitrogen molecule in its electronic ground state. Using the algebraic approximation, the energy is evaluated through third order, including all many-body effects. (2/1) Pade approximants and variational upper bounds are constructed. For one of the perturbation expansions considered, the (2/1) Pade approximant leads to the recovery of 79.5 percent of the empirical correlation energy, while the variational upper bound recovers 72.0 percent. Three-body effects are examined in some detail. The relationships with previous work on N2 are discussed.

Wilson, S.↗

NASA NTRS1977

Theoretical study of the butadiynyl and cyanoethynyl radicals - Support for the identification of C3N in IRC + 10216

Quantum-mechanical calculations, using the matrix Hartree-Fock model, have been performed for the butadiynyl and cyanoethynyl radicals. A rotation constant of 4753 MHz is calculated for C4H, while for C3N the value 4955 MHz is obtained. These may be compared with the rotation constant of 4947.5 MHz derived from the recently observed doublets in the millimeter-wave spectrum of IRC + 10216, suggesting the cyanoethynyl radical as the carrier species of these lines. The electric dipole moment and hyperfine coupling constants of both species are predicted.

Wilson, S.↗