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  • 1
    Electronic Resource
    Electronic Resource
    Theoretical analysis of electronic delocalization (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 1687-1697 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A block-localized wave function method is introduced to evaluate the electronic delocalization effect in molecules. The wave function for the hypothetical and strictly localized structure is constructed based on the assumption that all electrons and primitive basis functions can be divided into several subgroups; each localized molecular orbital is expanded in terms of primitive orbitals belonging to only one subgroup. The molecular orbitals belonging to the same subgroup are constrained to be mutually orthogonal, while those belonging to different subgroups are free to overlap. The final block-localized wave function at the Hartree–Fock level is expressed by a Slater determinant. In this manner, the energy difference between the Hartree–Fock wave function and the block-localized wave function can be generally defined as the electronic delocalization energy. The method is applied to two cases. The first concerns the resonance stabilization in the allyl ions. We find that the vertical resonance energies for the planar cation and anion are −45.7 (or −44.7) and −46.7 (or −48.2) kcal/mol at the HF/6-31G* (or 6-31+G*) level, respectively. Their rotational barriers are decomposed in terms of conjugation, hyperconjugation, steric effect, and pyramidalization. The n→σ* negative hyperconjugation in the staggered allyl anion is very strong and stabilizes the system by as much as −13 kcal/mol. The second concerns the hyperconjugation effect in propene. Our calculations suggest that the theoretical hyperconjugation energy in propene is about −5 kcal/mol, which is close to the experimental estimate (−2.7 kcal/mol) derived from the hydrogenation heats of propene and ethylene. Comparisons between the results based on the present block-localized wave function method and those based on the natural bond orbital method are presented and discussed. The examples demonstrate that the block-localized wave function method can be employed as a useful model to analyze chemical bondings and intuitive concepts. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.476742
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  • 2
    Electronic Resource
    Electronic Resource
    Theoretical investigation of the relation of hole-burning properties and the electronic structure of chemisorbed dyes (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 219-226 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The ground and first excited states of the organic dyes quinizarin (Q) and tetrahydroxyphenylporphyrin (TOHP) chemisorbed on γ-Al2O3 were investigated with semiempirical PM3 and multireference CI methods. Q/γ-Al2O3 and TOHP/γ-Al2O3 represent promising materials for frequency domain optical data storage (FDOS) based on persistent spectral hole burning (PSHB), since it is possible to detect spectral holes at high temperatures (77 K). To find out whether differences in the electronic structure between the free and the adsorbed molecules account for the hole-burning properties, we performed calculations of Q–Al complexes with various coordination spheres. The calculated vertical excitation energies for the first electronically excited state of the investigated structures are in good agreement with experimental data. Analysis of the molecular orbitals shows that complexation of the investigated molecules with Al affects the electronic structure of the dyes only little. Furthermore, the character of the first excited state is conserved. The change of the dipole moment between the ground and the first excited states is about the same for the free and for the complexated systems. Therefore, it is concluded that hole burning of dye molecules chemisorbed on γ-Al2O3 at high temperatures is not due to a change of the electronic structure of the adsorbed dye molecules compared to the free dye molecules, but has to be attributed to the special interactions of Q with the γ-Al2O3 surface. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469635
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  • 3
    Electronic Resource
    Electronic Resource
    Ab initio study of the vibronic and spin–orbit coupling in the X 2Πu state of C2H+2 (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 7142-7149 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A variational approach for treating the Renner–Teller effect in tetra-atomic molecules [Peric et al., Mol. Phys. 55, 1159 (1985)] is extended to account for the effect of spin–orbit coupling. The approach is applied to compute the spin–orbit splittings of the vibronic levels in the X 2Πu state of C2H+2. The bending potential curves employed in a previous study [Peric and Peyerimhoff, J. Chem. Phys. (in press)] are improved by carrying out ab initio calculations at a higher level of sophistication. The results of the computations enable a reliable interpretation of recent experimental findings [Pratt et al., J. Chem. Phys., 99, 66 (1993)]. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469108
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  • 4
    Electronic Resource
    Electronic Resource
    A comparative ab initio study of the Si2C4, Si3C3, and Si4C2 clusters (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 6790-6799 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Various structural possibilities for the Si2C4 and Si4C2 clusters are investigated by employing a basis set of triple-zeta plus polarization quality; electron correlation is generally accounted for by second-order Møller–Plesset and, in certain instances, by higher-order perturbation (CASPT2) approaches. The building-up principle recently suggested from an analysis of Si3C3 clusters is found to be fully operative for Si2C4 and Si4C2 clusters. A comparison of the structure and stability of various geometrical arrangements in the series C6, Si2C4, Si3C3, Si4C2, and Si6 shows that linear and planar structures become rapidly less stable if carbons are replaced by silicons and that the three-dimensional bipyramidal forms become less favorable as soon as silicons are exchanged by carbons in the parent Si6 structure. The effects can be rationalized in qualitative terms based on differences in silicon and carbon bonding.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468334
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  • 5
    Electronic Resource
    Electronic Resource
    Configuration interaction studies of low-lying valence and Rydberg states of NS (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 82 (1985), S. 2672-2678 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Using a better than double-zeta-plus-polarization basis set, the multireference-double-excitation-configuration-interaction (MRD-CI) method has been employed to calculate the potential curves for the X 2Π, a 4Π (unobserved), b 4Σ− (unobserved), B 2Π, 2Φ (unobserved?), A 2Δ, C 2Σ+ (Rydberg), H 2Π, I 2Σ+, and J 2Σ+ (Rydberg) states of the NS radical. Except for the B′ 2Σ+ state, which is not found in our calculations, all the calculated Te and re values for experimentally observed states are found to be in good agreement with experiment, whereas the calculated ωe's are only satisfactory. Arguments have been advanced to identify the experimental observed B′ 2Σ+ state as the calculated 2Φ state. The radiative lifetime for the v'=0 level of the C 2Σ+ state has been calculated to be about 30 ns, indicating the level predissociates since the experimental radiative lifetime is only 6.5 ns.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.448264
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  • 6
    Electronic Resource
    Electronic Resource
    Ab initio study of the locations and intensities of the lowest-lying electronic transitions of the C3 and C2O molecules (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 84 (1986), S. 268-274 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A series of ab initio SCF and CI calculations is reported for the C3 and C2O molecules in their lowest excited states. A large AO basis containing two primitive d functions on each atom and s- and p-type bond functions at the center of each bond is employed for C3 and CI secular equations of order 10 000 are solved based on a well-known configuration selection procedure. The location of the A 1Πu–X 1Σ+g transition is computed within an error of 0.07 eV relative to experiment and an oscillator strength of 0.052 is obtained for absorption, corresponding to a radiative lifetime for the A 1Πu state of 95 ns. The C 1Πg is found to lie only 0.838 eV above the A 1Πu state with a computed lifetime of 0.938 μs. Analogous calculations for the C2O molecule are carried out employing only a single primitive d function on each atom and geometrical optimization is undertaken for the (linear) X 3Σ− ground state. The A 3Πi, 1Σ+, 1Δ, and lowest two 1Π states are treated at the ground state equilibrium conformation, with the A–X transition energy again found to agree well with available experimental data; the lifetime of the A 3Πi state is calculated to be 0.773 μs. The relationship of the calculated results to problems of astrophysical interest is also discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.450180
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  • 7
    Electronic Resource
    Electronic Resource
    Theoretical studies on excited states of Ne2. I. MRD-CI potential energy curves (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 82 (1985), S. 353-363 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Using a 5s3p contracted Gaussian basis with d-polarization functions and 3s, 4s, 3p, and 4p diffuse functions, potential energy curves for excited states of Ne2 dissociating to Ne+Ne* (3s,3p,4s) were calculated by the MRD-CI method. Five singlet and triplet states each of Σ+g Σ+u, Πg, and Πu type, and one singlet and triplet state of Δg and Δu type were considered. The features of the potential curves are discussed and compared with those obtained by previous workers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.448753
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  • 8
    Electronic Resource
    Electronic Resource
    Ab initio investigation of the vibronic structure of the 3p 2Π (Rydberg) state of HCO and DCO (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 3587-3591 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The results of an ab initio investigation of the vibronic structure of the 3p 2Π (Rydberg) state of HCO and DCO are presented. The potential curves obtained by large-scale configuration interaction (CI) calculations are employed. The theoretical results confirm a recent experimental analysis of the Renner–Teller effect in this state.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464035
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  • 9
    Electronic Resource
    Electronic Resource
    Ab initio study of the three lowest states X 2∑+, 2Π1/2, 2Π3/2, and B 2∑+ of the HeNe+ ion: Potential energy curves, Λ doubling, and predissociation rates of the rotational levels in the 2Π1/2 (v=0) state (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 1165-1175 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Multireference configuration interaction calculations are performed for the X 2∑+, 2Π, and B 2∑+ states in HeNe+ from 2.2 to 100 bohr. The various perturbations of the Born–Oppenheimer states are evaluated: the spin–orbit interaction is calculated up to second order by employing the Breit–Pauli Hamiltonian. The resulting potential curves for the A 2Π1/2 state are compared with the experimental data of Dabrowski and Herzberg (Ref. 1), the curve of the hereto undetected A 2Π3/2 is predicted. The Λ splitting of the A1 2Π3/2 and the A2 2Π1/2 states due to coupling of the electronic motion with the rotation of the nuclear framework is computed by employing a basis of vibronic eigenfunctions. The calculated parameters of p0=−1.407 cm−1 for A2 2Π1/2 agree well with the corresponding data of p0=−1.417 or −1.427 cm−1 derived from measurements (Refs. 1 and 2). The predissociation rates of the rotational levels in the A2 2Π1/2 (v=0) state are also calculated on the basis of the computed ab initio data. All results are compared with the experimental data of Carrington (Ref. 2). The mechanism for the predissociation of the A 2Π1/2 state (in the absence of a curve crossing) is elucidated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459180
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  • 10
    Electronic Resource
    Electronic Resource
    Multireference singles and doubles configuration interaction study of the photoelectron spectrum of HO−2 (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 7229-7238 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Multireference singles and doubles configuration interaction (MRD-CI) electronic structure calculations are carried out on the hydroperoxyl radical and its negative ion. Potential energy curves of the ground state of the anion and of the ground and first excited states of the neutral molecule along the O–OH coordinate are employed to compute the Franck–Condon factors for the electron photodetachment processes HO2(X 2A‘,A 2A')+e←HO−2(X 1 A'). The theoretical spectrum agrees fairly well with the photoelectron spectrum reported by Oakes, Harding, and Ellison, and is consistent with their assignment of the peaks K and D as origins for the electron loss transitions to the HO2 A and X states, respectively. An alternative choice of peak E as X←X− origin yields better agreement between computed and experimental Franck–Condon factors than does the peak D assignment, but is less satisfactory when energetic considerations are taken into account. Two independent ab initio results lend support to the value of 1.078±0.017 eV for the measured adiabatic electron affinity of HO2, which is in good agreement with the best value inferred from the MRD-CI calculations of 1.069±0.05 eV. The matter is not settled, however, as some inconsistencies in the experimental data still cast some doubts on the assignment of the peaks and the accuracy of the HO2 EA.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456252
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