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  • 1
    Electronic Resource
    Electronic Resource
    Theoretical characterization of the minimum energy path for the reaction H+O2→HO2*→HO+O (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 6273-6281 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The potential energy surface for the reaction H+O2→HO@B|2 →HO+O has been characterized in the vicinity of the minimum energy path using CASSCF/contracted CI calculations with a basis set which is triple zeta valence quality plus three sets of polarization functions. CASSCF/CI calculations were carried out along the CCI minimum energy path. The latter calculation shows essentially no barrier for addition of an H atom to O2, in agreement with predictions made in earlier studies. The potential surface for recombination of OH and O is complicated by a crossing, at rOO (approximate)5.5a0, between the surface for electrostatic (OH dipole–O quadrupole) interaction and that for the formation of an O–O chemical bond. This surface crossing results in a small ((approximate)0.5 kcal/mol) barrier.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454466
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  • 2
    Electronic Resource
    Electronic Resource
    Theoretical study of the alkali and alkaline–earth monosulfides (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 6431-6437 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Ab initio calculations are used to determine accurate spectroscopic constants (re, ωe, De ) for the X 2Π and A 2Σ+ states of the alkali sulfides (LiS–RbS) and the X 1Σ+, a 3Π, and A 1Π states of the alkaline–earth sulfides (BeS–SrS). In contrast to the alkali oxides, all of the alkali sulfides have X 2Π ground states owing to the larger electrostatic interaction. For the X 1Σ+ states of the alkaline–earth sulfides, our recommended dissociation energies (D0 in eV) are BeS(3.27), MgS(2.32), CaS(3.29), and SrS(3.41), in overall good agreement with the (uncertain) experimental values. Our computed Te(a 3Π) and Te(A 1Π) values for BeS of 7269 and 8244 cm−1 are in excellent agreement with experiment. For the heavier alkaline–earth sulfides, our calculated Te(a 3Π) values (cm−1) are MgS(4218), CaS(6528), and SrS(6870), and our calculated Te(A 1Π) values are MgS(5068), CaS(6901), and SrS(7179). Core correlation increases the Te values for the a 3Π and A 1Π states of MgS, CaS, and SrS.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454429
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  • 3
    Electronic Resource
    Electronic Resource
    Theoretical study of the first and second negative systems of N+2 (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 329-336 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The potential curves for the X 2Σ+g, B 2Σ+u, C 2Σ+u, (1) 2Δu, (2) 2Δu, 4Πu, and 2Σ−u states of N+2 are determined using extended Gaussian basis sets and large CASSCF/multireference CI wave functions. The radial dependence of the electronic transition moments for the first and second negative systems of N+2 are determined, and used to compute Einstein coefficients and radiative lifetimes. Based on the calculated crossing points between the C 2Σ+u , 4Πu, and 2Σ−u states, the predissociation in the C 2Σ+u state for v'≥3 appears to first involve a spin–orbit induced crossing to the bound 2Σ−u state, followed by predissociation of this state by the 4Πu state, which crosses it on the outer limb (just above v'=3 of the C state). This is consistent with the accidental predissociation mechanism suggested by Lorquet and Lorquet.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454604
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  • 4
    Electronic Resource
    Electronic Resource
    Theoretical determination of the radiative lifetime of the A 2Σ+ state of OH (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 4665-4672 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The radiative lifetime of the A 2Σ+(v′=0, N′=1) state of OH has been computed, using the theoretical potentials and transition moment, to be 673 ns, in excellent agreement with two of the experimental values (686±14 and 693±10 ns) determined by laser excitation fluorescence. The electron correlation treatment has been calibrated using full CI (FCI) calculations in a [4s3p2d/2s1p] Gaussian basis set. When a δ orbital is included in the CASSCF/MRCI treatment, the transition moment is within 0.2% of the FCI value. A basis set study shows that the [6s5p4d2f1g/4s3p2d] ANO basis set employed in our study is probably within 1% of the basis set limit for the transition moment. The theoretical radiative lifetimes, which are expected to be lower bounds and accurate to 2%, are sufficiently accurate to rule out the slightly lower value determined by Hanle effect studies, and the higher values determined for the v′=0 N′=1 level by the high frequency deflection technique (HFD). The HFD lifetimes for higher N′ values, however, are in relatively good agreement with theory.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452829
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  • 5
    Electronic Resource
    Electronic Resource
    Theoretical study of the electron affinities of Cu, Cu2, and Cu3 (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 1041-1045 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Modified coupled pair functional (MCPF) calculations are shown to yield the electron affinities of Cu, Cu2, and Cu3 to nearly equal accuracy. The structural results for Cu−3, together with the experimental negative ion photoelectron results, show conclusively that Cu−3 is linear in its (1Σ+g) ground state. The weak feature in the Cu−3 photoelectron spectrum at an electron binding energy of 1.5 eV is due to ionization from the 3A'2 (equilateral triangle) excited state of Cu−3.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454272
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  • 6
    Electronic Resource
    Electronic Resource
    A full CI treatment of the 1A1,1B1, and 3B1 states of SiH2 (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 1420-1424 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Full CI calculations are presented for the 1A1,3B1, and 1B1 states of SiH2 at their respective equilibrium geometries and at geometries with the SiH bonds stretched. These results are compared with those obtained from single reference and multireference CI calculations. The computed Te values agree well with the full CI results provided that the effects of higher than double excitations are accounted for either by the Davidson correction or by a multireference approach. When the SiH bonds are stretched the single reference methods are not sufficiently flexible, and only CASSCF/MRCI achieves chemical accuracy (i.e., agrees with the full CI to 1 kcal/mol). Overall, the accuracy of the various approximate methods is very similar to that found for H2O, NH2, and CH2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452229
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  • 7
    Electronic Resource
    Electronic Resource
    Theoretical spectroscopic parameters for the low-lying states of the second-row transition metal hydrides (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 268-278 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Spectroscopic parameters (De,re,μe) are determined for the second-row transition metal hydrides using large valence basis sets in conjunction with relativistic effective core potentials (RECPs). All-electron calculations are also performed for YH and AgH to calibrate the RECP results. Electron correlation is incorporated using singles-plus-doubles configuration interaction (SDCI), the coupled pair functional (CPF) method, and a modified version (MCPF) of CPF. Although similarities exist between the bonding in the first- and second-row transition metal hydrides, the greater overlap of the d orbitals in the second row with the hydrogen 1s orbital, tends to lead to larger dissociation energies and some changes in the relative ordering of the states. For example, the ground state of ZrH is predicted to be a 2Δ state whose bonding involves 4d–5s hybrid orbitals, whereas in TiH the ground state is a 4Φ state with primarily 4s–1s bonding. The bonding in the second-row transition metal hydrides involves a mixture of all three atomic asymptotes, 4dn5s2, 4dn+15s1, and 4dn+2, whereas contribution from the 3dn+2 asymptote is unimportant in the first-row TM hydrides. However, the bonding is generally much simpler to describe in the second-row as compared with the first-row TM hydrides, and the spectroscopic parameters are much less sensitive to the level of correlation treatment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452617
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  • 8
    Electronic Resource
    Electronic Resource
    On the 3d 64s2 (5D)−3d 74s1 (5F) separation in Fe (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 5591-5594 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Full CI calculations to determine the 5D−5F separation in Fe using [5s4p2d], [5s4p3d], and [5s4p2d1f] basis sets show that the single reference SDCI procedure is accounting for most of the differential correlation energy in the 3d and 4s shells. The SDCI separation using a [7s6p4d4f2g] basis set, correlating only eight electrons and accounting for the dominant relativistic effects is 1.25 eV, compared to the experimental value of 0.875 eV. Adding the 3s and 3p electrons to the SDCI treatment reduces the separation to 1.06 eV. It is concluded that the differential effect of higher excitations becomes more important when the 3s and 3p electrons are correlated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452533
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  • 9
    Electronic Resource
    Electronic Resource
    Full CI benchmark calculations on CH3 (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 5600-5602 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Full CI calculations have been performed on the CH3 radical. The full CI results are compared to those obtained using CASSCF/multireference CI and coupled-pair functional methods, both at the equilibrium CH distance and at geometries with the three CH bonds extended. In general, the performance of the approximate methods is similar to that observed in calculations on other molecules in which one or two bonds were stretched.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452535
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  • 10
    Electronic Resource
    Electronic Resource
    Full CI benchmark calculations on N2, NO, and O2: A comparison of methods for describing multiple bonds (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 5595-5599 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Full configuration interaction (CI) calculations on the ground states of N2, NO, and O2 using a DZP Gaussian basis are compared with single-reference SDCI and coupled pair approaches (CPF), as well as with CASSCF multireference CI approaches. The CASSCF/MRCI technique is found to describe multiple bonds as well as single bonds. Although the coupled pair functional approach gave chemical accuracy (1 kcal/mol) for bonds involving hydrogen, larger errors occur in the CPF approach for the multiple bonded systems considered here. CI studies on the 1Σ+g state of N2, including all single, double, triple, and quadruple excitations show that triple excitations are very important for the multiple bond case, and accounts for most of the deficiency in the coupled pair functional methods.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452534
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