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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 8070-8082 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: For the electronic ground state of CO+2 the three-dimensional potential energy, electric dipole, and transition moment functions have been calculated from highly correlated multireference configuration interaction electronic wave functions. Along the antisymmetric stretching displacements the shape of the potential energy functions is found to be very sensitive to the electron correlation effect. Using a modified theoretical potential energy function rovibronic energy levels have been calculated variationally by the method of Carter and Handy. In this approach, anharmonicity, rotation–vibration, electronic angular momenta, and electron spin coupling effects have been accounted for. The vibronic band origins agree to within about 10 to 20 cm−1 with the available experimental data, and the rotational levels agree to within 0.01 cm−1 for low J values. Additional vibrational band origins have been predicted for energies up to 3200 cm−1. The anomalously low frequency of the antisymmetric stretching mode and its inverse anharmonicity in the X 2Πg state of CO+2 have been reproduced with the potential energy functions for the adiabatic states. Previously, it has been assumed that this effect is due to the vibronic coupling. The molecular parameters of one-dimensional effective Hamiltonians obtained from fits of the spectral data are compared with those derived from the theoretical potential.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 1889-1894 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Potential energy and dipole moment functions have been calculated using multireference configuration interaction (MRCI) techniques for CF+, SiF+, and CCl+ in their ground 1Σ+ and first 3Π electronic states with large Gaussian basis sets. Where experimental data is available, the MRCI values of re and ωe are accurate to within 0.006 A(ring) and 7 cm−1, respectively. The Te values for the a 3Π–X 1Σ+ transitions for CF+, SiF+, and CCl+are calculated to be 4.77±0.05 eV, 4.78±0.05 eV, and 3.19±0.05 eV (3.16 eV), respectively (experimental value in parentheses). Rotational and vibrational spectroscopic constants are also predicted for all three species in the 3Π state. Infrared transition probabilities have been calculated from the MRCI potential energy and dipole moment functions. Intense infrared transitions are predicted for all three species in both their ground and first excited state.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 6635-6644 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Highly correlated CEPA electronic wave functions have been used to calculate the three-dimensional potential energy and electric dipole moment functions of the X 1A' and a 3A‘ states of HCF. The analytic expansions of these functions have been employed in variational and perturbational calculations of the vibrational band origins and spectroscopic constants. For the singlet ground state the vibrational band origins agree with available experiments to within 2 to 20 cm−1, the rotational constants to within 0.04 cm−1. Theoretical spectroscopic constants of similar accuracy are presented also for the triplet state. The singlet–triplet separation is calculated to be 13.9 kcal/mol, in agreement with the experimental upper bound of 14.7±0.2 kcal/mol. The dipole moments (μ0) have been calculated to be 1.394±0.05 D (X 1A') or 1.049±0.05 D (a 3A‘), respectively, and vibrational radiative transition probabilities are also given. Anomalous variations of radiative lifetimes in some low-lying vibrational levels have been found in the singlet state of HCF which are due to anharmonic coupling effects.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 783-794 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The high resolution rovibrational spectrum of H2S has been evaluated from three-dimensional ab initio potential energy and electric dipole moment functions and variational rovibrational eigenfunctions, which took full account of anharmonicity effects and rotation–vibration coupling. The quality of the near equilibrium theoretical potential energy function has been checked by comparisons with experimental equilibrium structure, empirical quartic force fields, vibrational band origins, centrifugal distortion constants, and rotational energy levels. All parameters agree well with the available experimental data. Vibrational band intensities for the ν2, 2ν2, ν1, and ν3 bands have been calculated from empirical and ab initio dipole moment functions and compared with experimental and theoretical integrated band intensities. The difficulties arising by the derivation of such data from the experimental intensities of H2S are discussed. The theoretical results strongly suggest that higher than first derivatives are needed for a proper description of the dipole moment function. The room temperature absorption spectra have been evaluated ab initio for the pure rotational and the ν2, 2ν2, ν1, and ν3 transitions. The unusual intensity pattern of the P, Q, and R branches attributed to the rotational–vibrational coupling has been well reproduced. Absolute line intensities calculated previously by perturbation theory are compared with variational results. The purely theoretical line intensities agree satisfactorily with experiment for the bending transitions, however, the extremely flat regions of the dipole moment functions along the bond stretching displacements make the transition intensities very sensitive to the values of the dipole moment derivatives.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 2913-2918 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Potential energy surfaces of the three lowest bound electronic states (1 2A′, 2 2A′, and 2A″) of H2O− have been investigated by ab initio calculations using highly correlated electronic wave functions. Minima resulting from ion–quadrupole interactions between the O−(2P) and H2(1Σ+) fragments were found for linear 2Σ+ and 2Π O−⋅⋅⋅H2 structures. The corresponding dissociation energies amount to about 0.2 eV. The 2Σ+ (2A′) minimum is separated by a barrier from the H2O+e continuum, while the 2Π (2A″) state is connected via a similar barrier to another local minimum of 2Π symmetry originating from the ion–dipole interaction of OH(X 2Π) and H−(1S). Hence, in accordance with recent experimental findings of de Koning and Nibbering, the H2O− ion is found to be a bound species in ion–quadrupole or ion–dipole cluster structures.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 4687-4698 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Collision induced rotational alignment of N+2 ions drifting in a helium buffer gas is studied by quantum closed coupled calculations using an ab initio interaction potential obtained from multireference configuration interaction wave functions. New formulas are derived for the tensor cross sections. For a given velocity distribution of the collisional partners a set of kinetic equations is solved under steady-state conditions. The resulting alignment parameters are found to be smaller than the experimental values for the velocity distribution assumed so far in drift tube experiments. However, by modification of the anisotropy of this distribution, good agreement between the theoretical quadrupole moments of the rotational angular momentum distributions and the corresponding experimental data can be obtained. It is shown that the attractive part of the potential has a significant influence on the collision dynamics of the N+2–He system. The closed coupled m-resolved cross sections indicate that collision induced transitions between magnetic sublevels of a single rotational state contribute more to the alignment effect than transitions between different rotational states.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 2178-2184 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The two-dimensional interaction potential of the N+2(X 2Σ+g) –He(X 1S) system has been calculated using highly correlated ab initio MCSCF-CI wave functions for a fixed value of the N+2 bond length (2.110 a0). It is found to have a minimum about 140 cm−1 below the N+2 +He dissociation limit, significantly deeper than the minimum in the neutral system N2–He. This well depth is enough to give rise to a cluster-like, bound structure with a considerable number of vibration–rotation levels in the electronic ground state. The well depth is almost independent of the N2–He angle, which leads to large amplitude bending motions. Rovibrational calculations have been performed on the surface for J=0, 1, and 2. Values for the rotational constant B, the fundamental stretching frequency νs, and its first and second overtones, and the rotational constant Cn in each nνs manifold, have been obtained from the energy levels computed. It is found that B=1.879 cm−1, 1νs =55.231 cm−1, 2νs =83.404 cm−1, 3νs =92.491 cm−1, C0=0.477 cm−1, C1=0.370 cm−1, and C2=0.254 cm−1. Estimates of the accuracy of these parameters are made.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 6329-6336 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Near equilibrium three-dimensional potential energy and electric dipole moment surfaces of the bound negative ion HLiH− were calculated from highly correlated CEPA electronic wave functions. The HLiH− ion is linear with Re=1.743 A(ring). From the potential energy surface the anharmonic vibration–rotation term values were calculated variationally and by perturbation theory. The fundamental vibrational transitions in HLiH− are predicted to lie at ν1(J=0)=1014 cm−1, ν2(J=1)=429 cm−1, ν3(J=0)=1079 cm−1. The D0 dissociation energy relative to the LiH+H− asymptote is calculated to be 2.34 eV, the vertical electron detachment energy to be 3.10 eV. The components of the electric dipole moment surface are given analytically.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 82 (1985), S. 1420-1426 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Spectroscopic properties of SiO and HOSi+ have been calculated from hgihly correlated wave functions. HOSi+ is linear with re=0.959 A(ring) and Re=1.534 A(ring), but the bending potential is extremely flat. The wave numbers of the fundamental vibrations of H16O28Si+ (in cm−1) are predicted to be ν1=3658, ν2=248, and ν3=1110 with an uncertainty of about 20 cm−1. While the dipole moment of HOSi+ is very small (which will make detection of pure rotational transitions of this ion a difficult task), large intensities are predicted for stretching vibrational transitions both in absorption and emission. The proton affinity of silicon monoxide is calculated to be 8.44 eV.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 3593-3611 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The unimolecular dissociation of the formyl radical HCO in the electronic ground state is investigated using a completely new ab initio potential energy surface. The dynamics calculations are performed in the time-independent picture by employing a variant of the log-derivative Kohn variational principle. The full resonance spectrum up to energies more than 2 eV above the vibrational ground state is explored. The three fundamental frequencies (in cm−1) for the H–CO and CO stretches, and the bending mode are 2446 (2435), 1844 (1868), and 1081 (1087), where the numbers in parentheses are the measured values of Sappey and Crosley obtained from dispersed fluorescence excitation spectra [J. Chem. Phys. 93, 7601 (1990)]. In the present work we primarily emphasize the dissociation of the pure CO stretching resonances (0v20) and their decay mechanisms. The excitation energies, dissociation rates, and final vibrational–rotational state distributions of CO agree well with recent experimental data obtained from stimulated emission pumping. Similarities with and differences from previous time-independent and time-dependent calculations employing the widely used Bowman–Bittman–Harding potential energy surface are also discussed. Most intriguing are the pronounced oscillations of the dissociation rates for vibrational states v2≥7 which are discussed in the framework of internal vibrational energy redistribution. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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