SEARCH · Engineering Papers
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
The absolute values of photoionization cross sections of atomic oxygen were measured from the ionization threshold to 120 A. An auto-ionizing resonance belonging to the 2S2P4(4P)3P(3Do, 3So) transition was observed at 479.43 A and another line at 389.97 A. The experimental data is in excellent agreement with rigorous close-coupling calculations that include electron correlations in both the initial and final states.
In many important catalytic processes, the dissociation of the hydrogen molecule is a fundamental step, and the chemisorption of dihydrogen by metal surfaces has been studied. However, quantitative results from theoretical treatments are not very encouraging. Blomberg and Siegbahn (1983) have found that the negative binding energy for NiH2 obtained with the aid of the commonly used Hartree-Fock approximation differs greatly from the result found on the basis of a more sophisticated calculation, including electron correlation. Another study showed the great importance of d orbitals in the dissociation process. A study, similar to the one on NH2, has been conducted for three other metals, including cobalt, iron, and copper. The present investigation is concerned with the results of this study. The potential surfaces of CoH2, FeH2, and CuH2 are discussed, taking into account the lowest atomic states, the bent low spin complex, the bent high spin saddle points, and the linear states.
A number of molecular species on the H3CO(+) energy hypersurface is examined. Ab initio molecular orbital theory is used to determine the structures and relative energetics of the two isomers of HCO(+) and HOC(+) together with the affinity of CO for protonation at either end. The proton affinities of H2 and H2CO are also examined. The calculations are performed using large basis sets and include the effects of electron correlation. The calculated vibrational frequencies are used to correct for zero point energy differences. The results show that the proton affinities of H2 and CO to form HOC(+) are within 1 kcal of each other. The calculations demonstrate that there is no thermodynamic driving force to form HOC(+) in collisions of H3(+) with CO, and that the formation of HCO(+) in such collisions is very exoergic. A plausible mechanism is suggested to explain the differences observed between the laboratory and the interstellar medium.
The absolute values of photoionization cross sections of atomic oxygen were measured from the ionization threshold to 120 A. An auto-ionizing resonance belonging to the 2S2P4(4P)3P(3Do, 3So) transition was observed at 479.43 A and another line at 389.97 A. The experimental data is in excellent agreement with rigorous close-coupling calculations that include electron correlations in both the initial and final states.
In the context of their relevance to catalysis and to materials science problems, transition metals and transition metal (TM) compounds are currently of considerable interest, and studies have been conducted of the copper trimer, Cu3. The present investigation is concerned with a study of the ground state surface and several groups of excited states in order to improve the understanding of the spectroscopy of Cu3. Differences of the current study from previous investigations are related to an employment of larger basis sets and a more extensive electron correlation. This was done with the objective to obtain a more accurate definition of the ground state surface. Features of the bonding in the copper dimer are considered to obtain a basis for an understanding of the copper trimer. Attention is given to calculational details, the ground state surface, and calculated vertical excitation energies. The results of SCF/SDCI calculations are reported for portions of the ground surface, for two groups of excited states, and for the ionization potential of Cu3.
Theoretical potentials for the 7Sigma(u)+ state are reported using both extended Slater and Gaussian basis sets. Electron correlation is included using the interacting correlated fragments (ICF), the singles plus doubles configuration-interaction (SDCI), and the coupled-pair functional (CPF) approaches. The best potential, corrected for basis set superposition errors, has a well depth of about 21/cm and an r(e) of 7.52 bohr. The inclusion of the nitrogen 2s correlation significantly increases the well depth. These results are in reasonably good agreement with the empirical potential of Ferrante and Stwalley (1983), and support the contention that spin-polarized atomic nitrogen should behave like a classical solid such as Ne. It is shown that the modified Buckingham potential used by Ferrante and Stwalley is consistent with the present ab initio potentials if smaller values are used for the dispersion coefficients of the nitrogen atom.
A laser speckle, differential strain measurement system was built and tested for future applications in hostile environments. One dimensional electronic correlation of speckle pattern movement allows a quasi-real time measure of strain. The system was used successfully to measure uniaxial strain reaching into plastic deformation of a test specimen, at temperatures ranging to 450 C. A resolution of 16 microstrain is given by the photodiode array sensor pitch and the specimen to sensor separation. The strain measurement limit of the gauge is determined by air density perturbations causing decorrelation of the reference and shifted speckle patterns, and may be improved by limiting convective flow in the immediate vicinity of the test specimen.
A laser speckle, differential strain measurement system has been built and tested for future applications in hostile environments. One-dimensional electronic correlation of speckle pattern movement allows a quasi-real time measure of strain. The system has been used successfully to measure uniaxial strain reaching into plastic deformation of a test specimen, at temperatures ranging to 450 C. A resolution of 16 microstrain is given by the photodiode array sensor pitch and the specimen to sensor separation. The strain measurement error is estimated to be +/-18 microstrain +/-3 percent of the strain reading. The upper temperature limit of the gauge is determined by air density perturbations causing decorrelation of the reference and shifted speckle patterns, and may be improved by limiting convective flow in the immediate vicinity of the test specimen.
The potential energy function and electric dipole moment function (EDMF) are computed for ClO X 2Pi using several different techniques to include electron correlation. The EDMF is used to compute Einstein coefficients, vibrational lifetimes, and dipole moments in higher vibrational levels. The band strength of the 1-0 fundamental transition is computed to be 12 + or - 2 per sq cm atm determined from infrared heterodyne spectroscopy. The theoretical methods used include SCF, CASSCF, multireference singles plus doubles configuration interaction (MRCI) and contracted CI, coupled pair functional (CPF), and a modified version of the CPF method. The results obtained using the different methods are critically compared.
The discovery of cyclopropenylidene in space suggests that other C3H2 isomers may be present, and a tentative detection of one such isomer, propargylene (HCCCH), has been reported. Ab initio molecular orbital theory has been used to characterize five low-lying, metastable isomers of cyclopropenylidene. Extended calculations including the electron correlation energy, show that the lowest in energy is singlet propadienylidene, followed by propargylene; the singlet and triplet of the latter are too close in energy to allow an assignment of the ground state; triplet propadienylidene is at a significantly higher energy. Rotational frequencies computed to an expected accuracy of + or - 1 -2 percent do not confirm the tentative detection of propargylene in space, although the discrepancy between theory and the observation is not so great as to unequivocally rule out this possibility.
By means of near Hartree-Fock quality Slater basis sets, and the incorporation of electron correlation through the coupled-pair formalism, theoretical potentials are obtained for the X1Sigma(+) states of NaH, KH, and RbH. Electric dipole moment functions are given for NaH-RbH, as well as vibrationally averaged dipole moments, Einstein coefficients, and radiative lifetimes for the first 10 vibrational levels; an extensive study is made of the computational requirements for an accurate permanent dipole moment of KH.
A systematic analysis of the low-lying states of all of the second-row transition metal (TM) hydrides except CdH is reported. The calculations included the dominant relativistic contributions through the use of the relativistic effective core potentials of Hay and Wadt (1985). Electron correlation was incorporated, using single-plus-double configuration interaction, the coupled pair functional (CPF) formalism of Ahlrichs et al. (1985), and the Chong and Langhoff (1986) modified version of the CPF method. The spectroscopic parameters D(e), r(e), and mu(e) determined for the low-lying states are compared with the available experimental data and previous theoretical results. In contrast to the first-row TM hydrides studied earlier (Chong et al., 1986), the spectroscopic constants for the second-row TM hydrides were found to be much less sensitive to the level of correlation treatment.
The computational requirements for accurately describing the spectroscopic constants for all three candidates for the ground state of Al2 are determined. Full CI(FCI) calculations are used to calibrate approximate methods of including the electron correlation. CASSCF/MRCI calculations which accurately reproduce the FCI results in the valence DZ + 2d Gaussian basis are carried to chemical accuracy by using extensive one-particle basis sets. The effect of 2s and 2p correlation and relativistic effects are considered as well as the valence 3s and 3p correlation. Several excited states are also considered. It is shown that the computed vibrational frequency of the (2) 3Pi(g) state and the Franck-Condon factors for the (1) 3Pi(u) - (2) 3Pi(g) transition are consistent with the spectrum obtained by Douglas et al. (1983) and Abe and Kolb (1983). It is therefore concluded that the ground state is 3Pi(u).
The results of an ab initio molecular orbital investigation of the isoformyl cation, HOC(+), shape are reported. The effects of expanding the basis set to near the Hartree-Fock limit and of electron correlation were examined, and the results indicate that near the Hartree-Fock limit the HOC(+) is linear. An analytic potential function is presented, from which the calculated rotational energies are only 0.03 percent different from the experimental values. This represents a nearly two orders of magnitude reduction in error from earlier work.
A laser speckle, differential strain measurement system has been built and tested for future applications in hostile environments. One-dimensional electronic correlation of speckle pattern movement allows a quasi-real time measure of strain. The system has been used successfully to measure uniaxial strain reaching into plastic deformation of a test specimen, at temperatures ranging to 450 C. A resolution of 126 microstrain is given by the photodiode array sensor pitch and the specimen to sensor separation. The strain measurement error is estimated to be +/-18 microstrain +/-3 percent of the strain reading. The upper temperature limit of the gauge is determined by air density perturbations causing decorrelation of the reference and shifted speckle patterns, and may be improved by limiting convective flow in the immediate vicinity of the test specimen.
Full configuration-interaction (FCI) calculations are used to assess the relative ability of methods for truncating the n-particle expansion in describing the ionic-neutral curve crossing between the two lowest Sigma(+) states of LiF. While the FCI calculations yield a smooth dipole moment function, MRCI calculations based on CASSCF orbitals optimized for the lowest state at all r values yield a discontinuous dipole moment function. However, when the orbitals are optimized using a state-averaged CASSCF procedure, with equal weights for the ionic and neutral solutions, both the CASSCF and MRCI dipole moment functions are smooth and in reasonable agreement with the FCI. No single-reference-based method is found to work satisfactorily. Potential curves for the lowest two Sigma(+) states are determined in both the adiabatic and diabatic representations using a large atomic natural orbit Gaussian basis set and a state-averaged CASSCF/MRCI treatment of electron correlation.
Ab initio calculations on the NiCO(+) and TiCO(+) molecules are carried out using large Gaussian basis sets and extensive treatment of electron correlation. The NiCO(+) molecule is found to have a 2Sigma(+) ground state with a 2Delta state only 2.1 kcal/mole higher in energy. The Ni(+)-CO structure is about 11 and 28 kcal/mole more stable than the Ni(+)-OC and the T-shaped structures, respectively.
Ab initio calculations have been carried out for the X1Sigma(+), a3Delta, b3Delta(+), and c3Pi states of NiCO, using a large Gaussian basis set and an MCPF treatment of electron correlation. The calculated dissociation energies, De (kcal/mol), are 30.1, 11.5, 10.1, and 4.3 respectively. An analysis of the relative cross sections for photodetachment indicates the the lower energy feature in the photoelectron spectrum of NiCO(-) results primarily from bound-free transitions to the c3Pi state, with some contribution from bound-bound transitions to both the b3Sigma(+) and c3Pi states.