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  • 1
    Electronic Resource
    Electronic Resource
    Overtone intensities and dipole moment surfaces for the isolated CH chromophore in CHD3 and CHF3: Experiment and ab initio theory (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 7097-7109 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The band strengths of fundamentals (N=1) and overtones (up to N=6) of the strongly coupled CH stretching and bending vibrations in CHD3 and CHF3 are calculated using high level ab initio (SCF-CI) dipole moment functions and potential surfaces in one and two (three) dimensions. The calculations are performed in approximate normal coordinate and internal coordinate subspaces, the former giving generally superior results. The overall prediction of relative and absolute intensities ranging over many orders of magnitude is often accurate to within a factor of 2, but not to within experimental accuracy. Different dipole model functions and potential surfaces are investigated and an empirical adjustment of the dipole function to experiment is proposed for CHF3. The comparison of experimental and ab initio overtone intensities for the Fermi resonance system is discussed in some detail, as well as the importance of the results for IR spectroscopy and IR multiphoton excitation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459433
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  • 2
    Electronic Resource
    Electronic Resource
    Vibrational spectrum and potential energy surface of the CH chromophore in CHD3 (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 5408-5432 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The rovibrational spectrum of trideutero-methane has been measured at resolutions mostly close to the Doppler limit on an interferometric Fourier transform spectrometer from the lowest fundamental vibration to high overtones of the CH stretching vibration (wave numbers from 900 to 12 000 cm−1). The CH chromophore spectrum is fully assigned and interpreted by means of the tridiagonal Fermi resonance Hamiltonian for the coupled CH stretching and bending vibrations. The Hamiltonian predicts and also fits the visible spectrum up to 19 000 cm−1 measured by Scherer et al., Perry et al., and Campargue et al. The effective tridiagonal Hamiltonian is derived ab initio by means of MRD-CI and full CI calculations of the potential surface of methane, a variational vibrational calculation in a normal coordinate subspace of the coupled CH stretching and bending motions and an approximate similarity transformation to tridiagonal form. Fits of the experimental results by the tridiagonal and the variational Hamiltonian lead to equivalent spectroscopic constants. A careful experimental estimate of the main Fermi resonance coupling constant gives k'sbb (approximately-equal-to)(30±15) cm−1 in agreement with the best current ab initio result (31 cm−1). The ab initio potential in polar normal coordinates agrees with the potential derived from spectroscopic data covering an energy range of about 220 kJ mol−1 (more than half the dissociation energy). Good predictions are obtained for the parameters of the effective Hamiltonian, the spectral patterns, intensity distributions, and rotational constants in the Fermi resonance polyads. Three alternative interpretations of the parameters of the effective Hamiltonian are investigated and rejected on the basis of the available experimental and ab initio data. The results and conclusions are discussed in relation to intramolecular vibrational redistribution on the subpicosecond time scale and the recombination–dissociation kinetics of methane.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454552
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  • 3
    Electronic Resource
    Electronic Resource
    Vibrational spectrum, dipole moment function, and potential energy surface of the CH chromophore in CHX3 molecules (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 6698-6713 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The Fermi-resonance overtone spectra of the CH chromophore up to about 18 000 cm−1 are evaluated by variational vibrational calculations for the CHX3 molecules trideuteromethane (CHD3), trifluoromethane (CHF3), chloroform (CHCl3) and 1,1,1,3,3,3-hexafluoro-2-trifluoromethylpropane [(CF3)3CH]. Using appropriate model potential functions in a normal coordinate subspace, one can derive parameters for the CH chromophore potential and empirical dipole moment functions. For CHD3 and CHF3 ab initio (SCF-CI and vibrational variational) calculations are presented, the results of which compare well with the experiments and for CHD3 also with previous (MRD-CI) ab initio results. For all cases an accurate similarity transformation to the equivalent tridiagonal form of the effective hamiltonian can be made and the corresponding spectroscopic parameters agree with previous results. Comparison is also made with results from an internal coordinate model Hamiltonian.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457338
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  • 4
    Electronic Resource
    Electronic Resource
    The infrared and microwave spectroscopy of the argon–propyne dimer (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 6031-6043 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Microwave and infrared measurements are reported for the van der Waals complex Ar–CH3CCH and its isotopomers. The structure is T shaped with equilibrium center-of-mass separation of 3.73 A(ring) and an angle of 82° between the molecule symmetry axis and the van der Waals bond. The infrared and microwave spectra are complex due to the effects of a slightly hindered internal rotor. Analysis of the spectral data shows that the dipole moment is almost parallel to the dimer b axis. A modified vibration/rotation Hamiltonian that includes an internal rotor potential is used to show that the barrier to internal rotation is near 10.8 cm−1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464842
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  • 5
    Electronic Resource
    Electronic Resource
    Structure and energetics of small helium clusters: Quantum simulations using a recent perturbational pair potential (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 4596-4603 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report accurate ground state energies and structural properties for small clusters of 4He computed with the diffusion quantum Monte Carlo (DMC) method combined with high quality trial wave functions and using the recent analytical pair potential of Tang, Toennies, and Yiu [Phys. Rev. Lett. 74, 1546 (1995)]. Calculations based on the older HFD-B(He) potential are reported for comparison. The clusters are found to be extremely floppy and to be characterized by very diffuse wave functions. The DMC results for 4He2 and 4He3 are in excellent agreement with other calculations using conventional methods. 4He3 is found to have a noticeable contribution from nearly linear geometries. The internal structure of the clusters is described by a three particle correlation function which reveals a significantly non-spherical internal cluster structure. The energies for all cluster sizes are found to be slightly higher than those obtained with the HFD-B(He) pair potential. Exploratory calculations on the helium trimer indicate that the effects of three body interactions do not exceed the uncertainty margin provided by different state of the art pair potentials. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.473501
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  • 6
    Electronic Resource
    Electronic Resource
    Quantum Monte Carlo calculation of argon–HF clusters: Nonadditive forces, isomerization, and HF frequency shifts (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 1028-1039 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Zero point energies and structures have been calculated for ArnHF clusters (n=1–4) using the diffusion quantum Monte Carlo method and potential surfaces based on pairwise additive and non pairwise additive models. Energy differences for related potential surfaces are computed with a correlated sampling technique. The two lowest energy isomers of Ar4HF are found to be energetically equivalent if zero point energy effects are taken into account. Their energetic ordering depends sensitively on threebody contributions to the interaction potential. The calculated size dependent frequency shifts for fundamental and overtone transitions of HF caused by the argon micromatrix are in good agreement with experimental data but are sensitive to nonadditive forces. The line shifts cannot be explained quantitatively without accounting for zero point energy effects. The band origin of the yet unobserved C2v isomer of Ar4HF is predicted to be about 2.8 cm−1 to the red of the C3v isomer band. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470828
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  • 7
    Electronic Resource
    Electronic Resource
    Vibrational frequency shift of HF in helium clusters: Quantum simulation and experiment (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 8666-8683 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report accurate variational and diffusion quantum Monte Carlo calculations for the size dependence of the vibrational frequency shift of HF molecules embedded in helium clusters with up to n=198 helium atoms. The frequency shift exhibits a strong initial size dependence and saturates at a redshift of about 2.7 ± 0.1 cm−1 for clusters with over 100 atoms. This value is in good agreement with our experimental redshift of 2.65 ± 0.15 cm−1 for clusters with over 1000 atoms. The helium cluster is found to undergo significant structural changes upon embedding of HF. The density in the nearest neighbor shell exceeds the bulk helium density by a factor of two. A second nearest neighbor density maximum and a peripheral density plateau very close to the bulk helium value is found. In spite of the anisotropic interaction between HF and helium all clusters have almost perfectly spherical helium density profiles and indicate close to free rotor behavior of HF inside the cluster. The cluster size dependence of the redshift can be qualitatively described by an induced dipole model. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472648
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  • 8
    Electronic Resource
    Electronic Resource
    High Performance Computing in Chemistry (1998)
    Springer
    Journal of molecular modeling 4 (1998), S. 147-149 
    Details
    ISSN: 0948-5023
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s0089480040147
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  • 9
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    Probing the Structure and Dynamics of Molecular Clusters Using Rotational Wave Packets (2014)
    American Physical Society
    Details
    Publication Date: 2014-07-24
    Print ISSN: 0031-9007
    Electronic ISSN: 1079-7114
    Topics: Physics
    Published by American Physical Society
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  • 10
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    Impulsive alignment of 4He–CH3I: A theoretical study (2018)
    American Institute of Physics
    Details
    Publication Date: 2018-09-28
    Print ISSN: 0021-9606
    Electronic ISSN: 1089-7690
    Topics: Chemistry and Pharmacology , Physics
    Published by American Institute of Physics
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