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Bauschlicher, Charles W., Jr.

Publications and source records attributed to Bauschlicher, Charles W., Jr..

At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Triple and quadruple excitation contributions to the binding in Be clusters: Calibration calculations on Be3

The contribution of connected triple and quadruple excitations to the binding in Be3 is investigated by comparing various coupled-cluster (CC) and truncated configuration interaction (CI) treatments with multireference CI (MRCI) and full CI(FCI) calculations. The CC method with single and double excitations (CCSD) produces results that differ substantially from more elaborate treatments, but most extensions to CCSD that account approximately for connected triple excitations perform very well. In constrast, good agreement with FCI for Be2 can be achieved only with the highest level CC and MRCI methods.

Watts, John D.↗
NASA NTRS1991

Theoretical study of the spectroscopy of Al2(+)

The electronic states of Al2(+) below about 40,000/cm are studied using a CASSCF/MRCI approach in a large Gaussian basis set. The computed spectroscopic constants, excitation energies, Einstein coefficients, and radiative lifetimes should give insight into the spectroscopy of this ion.

Rosi, Marzio↗
NASA NTRS1991

The study of molecular spectroscopy by ab initio methods

This review illustrates the potential of theory for solving spectroscopic problems. The accuracy of approximate techniques for including electron correlation have been calibrated by comparison with full configuration-interaction calculations. Examples of the application of ab initio calculations to vibrational, rotational, and electronic spectroscopy are given. It is shown that the state-averaged, complete active space self-consistent field, multireference configuration-interaction procedure provides a good approach for treating several electronic states accurately in a common molecular orbital basis.

Bauschlicher, Charles W., Jr.↗
NASA NTRS1991

The bonding of multiple ligands to Mg(+) and Al(+)

The bonding of one to four waterligands to Mg(+) and Al(+) is studied. The bonding is very different from that found for multiple ligands bound to Na(+) or Cu(+). All the waters bind on the same side of the Mg or Al because of the polarization of the 3s orbital away from the ligands. Two benzene and methanol molecules also have a ligand-Mg-ligand angle of less than 180 deg with the angle determined by ligand-ligand repulsion.

Bauschlicher, Charles W., Jr.↗
NASA NTRS1991

Heteronuclear transition metal diatomics - The bonding and electronic structure of ScNi, YNi, ScPd, and YPd

High quality ab initio calculations show that ScNi, YNi, ScPd, and YPd all have 2Sigma(+) ground states in agreement with electron spin resonance experiments. For ScNi and YNi, this is expected based on the lowest atomic asymptote. For ScPd and YPd, the lowest atomic asymptote would give the order of stability 2Delta greater than 2Pi equal to about 2Sigma(+), but the calculations show that mixing in of the excited asymptotes preferentially lowers the 2Sigma(+) state. The calculations show that the quartet states are about 20-30 kcal/mol above the ground state, and therefore probably do not contribute significantly to the unexpected g(vertical) values found in experiment. Calculations of excited states for YPd reveal some strong transitions that should be amenable to spectroscopic studies.

Faegri, Knut, Jr.↗
NASA NTRS1991

The 2S(+) - 2P separation in KO

The 2S(+) - 2P separation in KO is investigated using large basis sets and high levels of correlation treatment. Relativistic effects are included at the Dirac-Fock level and reduce the separation only slightly. The basis set superposition error is considered in detail. On the basis of these calculations, our best estimate places the 2p sub 3/2 state about 200 cm(exp -1) above the ground 2 sigma(+) state in agreement with our previous estimate.

Bauschlicher, Charles W., Jr.↗
NASA NTRS1991

Theoretical study of the spectroscopy of the alkali oxides LiO, NaO, and KO

A state-averaged complete-active-space self-consistent-field multireference configuration-interaction method is presented to characterize the bound-bound emission from the CPi-2 state into the two lowest ionic states of LiO, NaO, and KO. Ab initio calculations use the experimental results obtained by Woodward et al. (1989) of the emitting state as CPi-2, but indicate that the tentative experimental band assignments are incorrect.

Langhoff, Stephen R.↗
NASA NTRS1990

Triple and quadruple excitation contributions to the binding in Be clusters - Calibration calculations on Be3

The contribution of connected triple and quadruple excitations to the binding in Be3 is investigated by comparing various coupled-cluster (CC) and truncated configuration-interaction (CI) treatments with multireference CI (MRCI) and full CI (FCI) calculations. The CC method with single and double excitations (CCSD) produces results that differ substantially from more elaborate treatments, but most extensions to CCSD that account approximately for connected triple excitations perform very well. In contrast, good agreement with CFI for Be2 can be achieved only with the highest level CC and MRCI methods.

Watts, John D.↗
NASA NTRS1990

Theoretical study of the homonuclear tetramers and pentamers of the group IB metals (Cu, Ag, and Au)

The optimal structures of the homonuclear tetramers and pentamers of Cu, Ag, and Au are found to be planar trapezoidal. However, on the basis of spin densities deduced from electron spin resonance experiments, it has been suggested that these pentamers have distorted trigonal bipyramidal structures. This apparent discrepancy is reconciled by the fact that Mulliken populational analyses indicate that the open-shell spin density distribution on the planar structures are also consistent with experiment. Since the vertical electron attachment energies for both the tetramers and pentamers are in good agreement with experiment, the negative ions probably also have planar trapezoidal structures. The trends in ionization potentials, atomization energies, and electron affinities with cluster size are discussed.

Bauschlicher, Charles W., Jr.↗
NASA NTRS1990

Theoretical study of the spectroscopy of NO(+)

The spectroscopy of the NO(+) molecule has been studied using multireference configuration-interaction calculations. The peak at 21.7 eV in the photoelectron spectrum of NO is assigned to the (2) 3Pi state (c 3Pi) and the vibrational progression centered at 23.1 eV is assigned to the diabatic (3) 1Pi state (B 1Pi). Several additional bound states with binding energies in excess of 1 eV are characterized in the present work. Radiative lifetimes are presented for many of the states.

Partridge, Harry↗
NASA NTRS1990

Theoretical study of the C-H bond dissociation energy of C2H

A theoretical study of the convergence of the C-H bond dissociation energy D(0) in C2H with respect to both the one- and n-particle spaces is presented. The calculated C-H bond energies of C2H2 and C2H4, which are in excellent agreement with experiment, are used for calibration. The best estimate for D(0) of 112.4 + or - 2.0 kcal/mol is slightly below the recent experimental value of 116.3 + or - 2.6 kcal/mol, but substantially above a previous theoretical estimate of 102 kcal/mol. The remaining discrepancy with experiment may reflect primarily the uncertainty in the experimental D(0) value of C2 required in the analysis.

Bauschlicher, Charles W., Jr.↗
NASA NTRS1990

The permanent electric dipole moment of CaOH

The X 2 Sigma(+), A 2Pi, and B 2Sigma(+) states of CaOH are characterized theoretically and experimentally, with a focus on the value of the permanent electric dipole moment (mu). Calculations based on SCF and SDCI studies of CaOH (Bauschlicher et al., 1984 and 1986) give mu values of 0.98, 0.49, and 0.11 D for the X, A, and B states, respectively, in good agreement with experiments in which the pure rotational spectra of these states were not detected. Modified Rittner (1951) and ligand-field models of these states are explored in detail, and the applicability of these results to observational searches for CaOH in circumstellar envelopes is indicated.

Bauschlicher, Charles W., Jr.↗
NASA NTRS1990

Theoretical study of the A 3Sigma(-)-X 3Pi transition in SiC

A theoretical study of the A 3Sigma(-)-X 3Pi infrared transition in SiC is presented using atomic natural orbital Gaussian basis sets in conjuction with multireference configuration interaction calculations. Dipole moment functions have been computed for both states as well as the A-X electronic transition moment function. The calculations predict that T(00) is 3700 + or - 200/cm, so that the transition recently observed in emission near 4500/cm and assigned to the 0-0 band of the A 3Sigma(-)-X 3Pi system of SiC is actually the 1-0 band.

Langhoff, Stephen R.↗
NASA NTRS1990

On the dissociation energy of BH

The dissociation energy D(0) of the X 1Sigma(+) state has been determined to be 81.5 + or - 0.5 kcal/mol. This value includes an estimate for basis set incompleteness and for core-core and core-valence correlation. The barrier in the A 1Pi state potential is estimated to be 1.9 + or - 0.2 kcal/mol. By analyzing the tunneling through the barrier, it is demonstrated that D(0) and the predissociation limit differ by about 0.8-0.9 kcal/mol. Thus the experimental predissociation limit of 82.5 + or - 0.4 kcal/mol is consistent with the values computed for D(0) and the barrier in this work.

Bauschlicher, Charles W., Jr.↗
NASA NTRS1990

Theoretical studies of the first- and second-row transition-metal mono- and dicarbonyl positive ions

Ab initio calculations have been carried out on the first- and second-row transition-metal mono- and dicarbonyl positive ions. The bonding in these systems is discussed in detail. Trends in the series of mono- and dicarbonyl ions and between the first- and second-row transition metals are explained in terms of a dominantly electrostatic bonding interaction and differences in metal ion state separations, ionization potentials, and s and d orbital sizes. Dissociation energies are presented and a detailed comparison is made with experimental data. Where reliable experimental data exists, agreement with the theoretical results is generally good.

Barnes, Leslie A.↗
NASA NTRS1990

On the dissociation energy of Mg2

The bonding in the X 1Sigma(+)g state of Mg2 is investigated using near-complete valence one-particle Slater and Gaussian basis sets containing up to h functions. It is shown that the four-electron complete CI limit can be approached using a sequence of either second-order CI (SOCI) or interacting correlated fragment (ICF) calculations. At the valence level, the best estimate of the dissociation energy D(e) was 464/cm. This is a lower limit and is probably within 5/cm of the complete basis value.

Partridge, Harry↗