ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

X
feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Electronic Resource
    Electronic Resource
    Perturbative calculations of vibrational (J=0) energy levels of linear molecules in normal coordinate representations (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 3476-3487 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Canonical Van Vleck perturbation theory is used to transform curvilinear and rectilinear normal coordinate vibrational Hamiltonians of HCN, C2H2, and CO2 to block-diagonal effective Hamiltonians. Accurate energies as high as 11 000 cm−1 above the zero point are reported for all three molecules. In the absence of off-diagonal coupling terms in the effective Hamiltonians, these two coordinate systems yield identical perturbative expansions for the vibrational energies. Only when coupling terms are introduced do differences between the calculated energies in the two representations become apparent. In CO2, where there is pronounced configuration interaction between nearly degenerate states, we find that the perturbative energies obtained from the curvilinear normal coordinate Hamiltonian are converging significantly faster than those obtained in the rectilinear normal coordinate representation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460850
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    Rotationally induced vibrational mixing in formaldehyde (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 2672-2683 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Almost-degenerate perturbation theory is used to derive an effective Hamiltonian describing the vibrational states of H2CO. Eigenvalues have been determined for energies up to 8600 cm−1 above the zero-point energy. Both curvilinear and rectilinear representations of the vibrational dynamics are presented and explored. Although differences are observed between the two effective Hamiltonian matrix elements, their eigenvalues generally agree to better than a wave number for the energies studied. Using the Watson Hamiltonian, the mechanism of rotationally induced vibrationally mixing is investigated as a function of K, the projection of the total angular momentum onto the body-fixed a axis. The combination of a-axis Coriolis coupling and Fermi couplings leads to extensive vibrational mixing between the rotational–vibrational states in this energy regime.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455965
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Theoretical studies of vibrationally excited polyatomic molecules using canonical Van Vleck perturbation theory (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 4378-4390 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The highly excited vibrational states of polyatomic molecules are investigated using canonical Van Vleck perturbation theory, implemented in a superoperator framework. This approach is used to transform a vibrational Hamiltonian to a new representation which has a form ideally suited to the study of the dynamics of interest. The key advantage is that the solution to the full problem is obtained in the new representation using significantly smaller basis sets than are needed to obtain the solutions in the original representation. The transformations are applied to the Hamiltonian operator itself, not the Hamiltonian matrix; this superoperator approach obviates the need for large basis sets. The tedious and complex algebra, that is required to perform these transformations, is readily implemented with FORTRAN codes. Combining these two features has enabled the investigations of vibrational dynamics in energy regimes and densities of states, unattainable by standard methods. These methods are applied to two model problems and to the study of the highly excited overtones of CHD3 with up to five quanta of excitation in the CH bond.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453797
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 4
    Electronic Resource
    Electronic Resource
    Rotation–vibration interactions between the two lowest frequency modes in formaldehyde (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 7201-7216 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Rotation–vibration interactions between the two lowest frequency normal modes of H2CO, the out-of-plane bend and the in-plane wag, are studied using classical trajectories. The dynamics is investigated for a range of rotational angular momenta, J, and energy values. Vibrational energy flow is elucidated by examining trajectories in several different canonical representations. The a-axis Coriolis term, which is quadratic in the normal coordinates, accounts for most of the coupling, as seen by comparing plots in the normal mode representation and one in which the Coriolis term has been subsumed into the zero-order Hamiltonian. In the former, the modes are more strongly coupled as the projection of J onto the body-fixed z axis increases; in contrast, the Coriolis adapted normal modes are more decoupled. Making use of the observed decoupling, the rovibrational Hamiltonian is reduced to an effective one degree-of-freedom rotational Hamiltonian whose dynamics depends on the vibrational excitation. Model spectra have been obtained using the semiclassical method of Gaussian wave packet propagation of Heller [J. Chem. Phys. 62, 1544 (1975)]. Semiclassical and full quantum results analogous to the observed classical dynamics are presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455299
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 5
    Electronic Resource
    Electronic Resource
    Complete active space self-consistent field potential energy surfaces, dipole moment functions, and spectroscopic properties of O3, CF2, NO−2, and NF+2 (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 414-430 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Three-dimensional potential energy and dipole moment surfaces have been calculated for the 24 electron triatomics O3, CF2, NO−2, and NF+2 using complete active space self-consistent field wave functions (CASSCF) and a basis set of 87 (99 for NO−2) contracted Gaussian-type orbitals (cGTOs). The analytical potential energy functions (PEFs) have been used in perturbation and variational calculations of anharmonic spectroscopic constants and vibrational energy levels. The results for O3 and CF2 are compared to the available experimental data, and predictions of the rotational and vibrational spectra of NO−2 and NF+2 have been made by comparison to these species. The equilibrium geometries of NO−2 and NF+2 are predicted to be re=1.260 A(ring), θe=116.5° and re=1.242 A(ring), θe=108.0°, respectively. The fundamental vibrational frequencies (ν1,ν2,ν3) and absolute band intensities (at 300 K) of these two ions are predicted to be 1286 cm−1/31 cm−2 atm−1, 782 cm−1/13 cm−2 atm−1, 1232 cm−1/2900 cm−2 atm−1 (NO−2) and 1272 cm−1/181 cm−2 atm−1, 711 cm−1/25 cm−2 atm−1, 1210 cm−1/1230 cm−2 atm−1 (NF+2). Band intensities for several low-lying vibrational transitions have been calculated for all four species from the CASSCF dipole moment functions, and comparisons to experiment have been made for O3 and CF2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460357
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 6
    Electronic Resource
    Electronic Resource
    Theory of vibrationally mediated photodissociation of HOOH: Delocalized tails in a localized wave function (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 6519-6545 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The vibrationally mediated photodissociation (VMP) of hydrogen peroxide [T. M. Ticich et al., J. Chem. Phys. 87, 5820 (1987)] is modeled. The two-photon VMP process proceeds via a highly vibrationally excited state on the ground electronic surface, and affords a unique view of the dynamics in the high energy region of the potential energy surface. We calculate, in a local mode basis set, the third OH stretch overtone wave function using the ground potential energy surface of Harding [L. B. Harding, J. Phys. Chem. 93, 8004 (1989)]. Although the overtone wave function is highly localized in the excitation mode, the delocalized tails which extend into the wide amplitude OO stretch region are crucial to the VMP mechanism. Interferences between zero-order states comprising these tails are shown to lead to a single state's being excited, the latter suggested by the VMP spectrum. The low frequency torsional mode is seen to play an important role in the makeup of the wave function.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460280
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 7
    Electronic Resource
    Electronic Resource
    Variable curvature coordinates for molecular vibrations (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 350-363 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A class of curvilinear coordinates for describing molecular vibrations is presented. The coordinates are parametrized by their curvature. Eigenvalues and eigenfunctions for three model Hamiltonians have been calculated in these coordinates. We investigate how the separability of the eigenfunctions varies as the curvature of the coordinates is changed, and we introduce a quantitative measure of separability using natural modal expansions. For the C–H stretch–bend interaction in CHD3, improved separability is found when coordinates are used which have a greater curvature than bond-angle coordinates. We predict and explain the results of Sibert et al. [J. Phys. Chem. 87, 2032 (1983)], who found the Fermi coupling between the bend and symmetric stretch in CO2 to be the same in rectilinear and curvilinear coordinates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457467
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 8
    Electronic Resource
    Electronic Resource
    A three-dimensional semiclassical quantization of H2O (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 5092-5104 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The semiclassical mechanics of the vibrations of H2O is examined. The analysis makes use of the work of Sibert, Reinhardt, and Hynes [J. Chem. Phys. 77, 3595 (1982)] in which the two-dimensional stretching dynamics of "local mode'' molecules was examined. There an approximate but accurate Hamiltonian was derived via the techniques of nonlinear mechanics. Quantization of this Hamiltonian, which has the form of a hindered rotor, gives vibrational energies in excellent agreement with direct quantum calculations of the H2O model Hamiltonian. In the present treatment we significantly advance the techniques developed in the earlier work to incorporate the bending degree of freedom and to generalize the treatment to be able to examine more realistic potential energy surfaces. Our results, which extend to energies as high as 22 000 cm−1, are in good agreement with the corresponding quantum mechanical calculation of Child and Lawton [Chem. Phys. Lett. 87, 217 (1982)] and demonstrate that a twofold hindered rotor Hamiltonian provides a good description of the three-dimensional vibrational eigenvalues.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.449723
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 9
    Electronic Resource
    Electronic Resource
    Vibrational relaxation in liquid chloroform following ultrafast excitation of the CH stretch fundamental (2002)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 116 (2002), S. 237-257 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Vibrational energy flow in liquid chloroform that follows the ultrafast excitation of the CH stretch fundamental is modeled using semiclassical methods. Relaxation rates are calculated using Landau-Teller theory and a time-dependent method both of which consider a quantum mechanical CHCl3 solute molecule coupled to a classical bath of CHCl3 solvent molecules. Probability flow is examined for several potentials to determine the sensitivity of calculated relaxation rates to the parameters that describe the model potentials. Three stages of relaxation are obtained. Probability is calculated to decay initially to a single acceptor state, a combination state of the solute molecule with two quanta of excitation in the CH bend and one in the CCl stretch, in 13–23 ps depending on the potential model employed. This is followed by rapid and complex intramolecular energy flow into the remaining vibrational degrees of freedom. During this second stage the lowest frequency Cl–C–Cl bend is found to serve as a conduit for energy loss to the solvent. The bottleneck for relaxation back to the ground state is predicted to be the slow 100–200 ps relaxation of the CH bend and CCl stretch fundamentals. Several aspects of the incoherent anti-Stokes scattering that follows strong infrared excitation of the CH fundamental as observed by Graener, Zürl, and Hoffman [J. Phys. Chem. B 101, 1745 (1997)] are elucidated in the present study. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1420488
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 10
    Electronic Resource
    Electronic Resource
    Distributed Gaussian polynomials and associated Gaussian quadratures (1997)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 38 (1997), S. 4815-4831 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: An orthogonal function set called distributed Gaussian orthogonal polynomials is constructed from equally spaced Gaussians and the corresponding quadrature is studied. The infinite chain limit of both polynomials and the quadrature is studied and analytical expressions are found for polynomials, quadrature points, weights, and Lagrange functions. The connections to Wannier functions are explored, and a way of constructing Wannier functions from Gaussians is proposed. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.532126
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...