Library

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
    Ultraviolet spectroscopy of water clusters: Excited electronic states and absorption line shapes of (H2O)n, n=2–6 (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 8747-8750 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A semiempirical model is developed, based on ab initio calculations, to provide an analytic representation of excited-state potential energy surfaces for (H2O)n, n=2–6. Using quantum calculations of the ground vibrational states, the UV absorption spectra are computed by a semiclassical approximation, showing a strong blue-shift with extended blue tails relative to the monomer, but with an additional red tail in the case of the dimer absorption band. The nature of the excitonic states is discussed. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.477542
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    Photodissociation dynamics of HCl in solid Ar: Cage exit, nonadiabatic transitions, and recombination (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 6574-6587 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The photodissociation of HCl in solid Ar is studied by non-adiabatic Molecular Dynamics simulations, based on a surface-hopping treatment of transitions between different electronic states. The relevant 12 potential energy surfaces and the non-adiabatic interactions between them were generated by a Diatomics-in-Molecules (DIM) approach, which incorporated also spin-orbit coupling. The focus of the study is on the non-adiabatic transitions, and on their role both in the cage-exit of the H atom, and in the recombination process. It is found that non-adiabatic transitions occur very frequently. In some of the trajectories, all the 12 electronic states are visited during the timescale studied. At least one non-adiabatic transition was found to occur even in the fastest cage-exit events. The other main results are: (1) The total yields for photofragment separation (by cage exit of the H atom) and for H+Cl recombination onto the ground state are roughly equal in the conditions used. (2) The cage exit events take place in the time-window between ∼70 fs and ∼550 fs after the excitation pulse, and are thus all at least somewhat delayed. The recombination events span a much broader time-window, from almost immediately after excitation, and up to ∼1100 fs and beyond. (3) The electronic energy relaxation events during the process depend significantly on symmetry and interactions of the states involved, and not only on the energy gaps between them. (4) Different electronic states reached in the course of the process exhibit different propensities with regard to the recombination versus cage exit outcome. (5) Spin-orbit interactions, and spin-forbidden transitions play an important role in the process, especially for recombination events. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.473657
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Ab initio calculation of anharmonic vibrational states of polyatomic systems: Electronic structure combined with vibrational self-consistent field (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 1823-1829 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An algorithm for first-principles calculation of vibrational spectroscopy of polyatomic molecules is proposed, which combines electronic ab initio codes with the vibrational self-consistent field (VSCF) method, and with a perturbation-theoretic extension of VSCF. The integrated method directly uses points on the potential energy surface, computed from the electronic ab initio code, in the VSCF part. No fitting of an analytic potential function is involved. A key element in the approach is the approximation that only interactions between pairs of normal modes are important, while interactions of triples or more can be neglected. This assumption was found to hold well in applications. The new algorithm was applied to the fundamental vibrational excitations of H2O, Cl−(H2O), and (H2O)2, using the Möller–Plesset method for the electronic structure. The vibrational frequencies found are in very good accord with experiments. Estimates suggest that this electronic ab initio/VSCF approach should be feasible, with reasonable computational resources, for all-mode calculations of vibrational energies and wave functions for systems of up to 10–15 atoms. The new method can be also very useful for testing the accuracy of electronic structure codes by comparing with experimental vibrational spectroscopy. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479452
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 4
    Electronic Resource
    Electronic Resource
    Photodissociation of HCl adsorbed on the surface of an Ar12 cluster: Nonadiabatic molecular dynamics simulations (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 11047-11053 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The photodissociation of HCl adsorbed on the surface of an Ar12 cluster is studied by semiclassical molecular dynamics simulations, using a surface-hopping approach for the nonadiabatic transitions. The DIM method is used to construct the 12 potential energy surfaces that are involved, and the nonadiabatic couplings. The results are compared with previous studies on HCl embedded inside Ar clusters and on the triatomic Ar–HCl cluster. The main findings are the following: (1) There is a yield of about 1% for recombination onto the ground electronic state of HCl, roughly the same as for HCl embedded inside Ar12. (2) Photodissociation lifetimes much longer than for Ar–HCl are found. (3) The kinetic energy distribution of the H atom shows large energy transfer to the cluster, greater than in the case of HCl in the embedded geometry in (Ar)12HCl. (4) An interesting mechanism leads to the formation of some fraction of very "hot" Cl atoms. (5) About 10% of the Cl is left trapped in (Ar)mCl clusters. (6) The branching ratio P1/2:P3/2 for the Cl atoms that leave the cluster shows electronic cooling compared to the isolated HCl molecule case. The results throw light on the role of local geometry in photodissociation/recombination processes, and in particular on the mechanisms pertinent in the case of surface-adsorbed species. The nature of the results, showing strong cage effects at the surface geometries is to a large extent a consequence of the encapsulation of the H atom, obtained for the structure of the (Ar)12HCl cluster. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479041
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 5
    Electronic Resource
    Electronic Resource
    Direct calculation of anharmonic vibrational states of polyatomic molecules using potential energy surfaces calculated from density functional theory (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 2598-2604 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Potential energy surface points computed from variants of density functional theory (DFT) are used to calculate directly the anharmonic vibrational frequencies of H2O, Cl−H2O, and (H2O)2. The method is an adaptation to DFT of a recent algorithm for direct calculations of anharmonic vibrational frequencies using ab initio electronic structure codes. The DFT calculations are performed using the BLYP and the B3LYP functionals and the results are compared with experiment, and also with those calculated directly from a potential energy surface obtained using ab initio Möller-Plesset second–order perturbation theory (MP2). The direct calculation of the vibrational states from the potential energy points is performed using the correlation-corrected vibrational self-consistent field (CC-VSCF) method. This method includes anharmonicity and correlations between different vibrational modes. The accuracy of this method is examined and it is shown that for the experimentally measured transitions the errors in the CC-VSCF calculations are much less than the errors due to the potential energy surface. By comparison with the experimentally measured frequencies the CC-VSCF method thus provides a test for the quality of the potential energy surfaces. The results obtained with the B3LYP functional, in contrast to those of the BLYP functional, are of comparable quality to those obtained with MP2. The B3LYP anharmonic frequencies are in good agreement with experiment, showing this DFT method describes well the anharmonic part of the potential energy surface. The BLYP results systematically underestimate both the harmonic and anharmonic frequencies and indicate that using this functional for the description of hydrogen-bonded systems may cause significant errors. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480833
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 6
    Electronic Resource
    Electronic Resource
    Quantum dynamics simulations of nonadiabatic processes in many-atom systems: Photoexcited Ba(Ar)10 and Ba(Ar)20 clusters (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 5803-5814 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Quantum simulations are reported for the dynamics following the photoexcitation Ba(1S)→Ba(1P) in Ba(Ar)10 and Ba(Ar)20 clusters. The evolution in time is studied in a framework that treats quantum-mechanically all the coupled degrees of freedom. The focus is on the role of nonadiabatic transitions between the three adiabatic surfaces corresponding to the P states of the Ba atom. The time scales of electronic relaxation and of electronic depolarization (orbital reorientation) are computed, and the competition between adiabatic and nonadiabatic effects is assessed. The calculations are carried out by a new scheme that extends the recent classically based separable potential method. Semiclassical surface-hopping simulations are used to produce effective single-mode potentials on which nuclear "orbitals'' are then generated. The full wave packet is constructed from the electronic states involved, and from these nuclear wave functions. Among the main results we find that nonadiabatic transitions become appreciable around 1 ps after photoexcitation, and they are stronger in the smaller cluster. Comparing Tully's semiclassical method with the quantum simulations, good qualitative agreement is found. Quantitatively, the semiclassical predictions for the electronic states branching rations deviate from the quantum results roughly by a factor of 2 after 1 ps. In the smaller cluster direct dissociation of the Ba atom dominates over energy redistribution within the cluster, the opposite being true for the large system. This example demonstrates the feasibility of quantum simulations of nonadiabatic processes in large systems with the new method. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471312
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 7
    Electronic Resource
    Electronic Resource
    Semiclassical molecular dynamics simulations of low-temperature clusters: Applications to (Ar)13; (Ne)13; (H2O)n, n=2,3,5 (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 1121-1130 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Semiclassical molecular dynamics simulations are developed as a tool for studying anharmonic clusters and solids at energies near the zero point. The method employs the time-dependent self-consistent-field approximation, that describes each mode as moving in the mean dynamical field of all other modes. The method further describes each mode by a semiclassical Gaussian wave packet. The scheme is carried out in normal modes. The method is restricted to systems of moderate anharmonicity at low temperatures. It is, however, computationally efficient and practically applicable to large systems. It can be used for the dynamics of nonstationary states as well as for stationary ones. Structural, dynamical and a variety of spectroscopic properties can easily be evaluated. The method is tested for thermal equilibrium states of (Ne)13, (Ar)13 against "numerically exact'' quantum Feynman path integral simulations. Excellent quantitative agreement is found for the atom–atom pair distribution functions. The method is also applied to (H2O)n clusters. Good agreement is found with experimentally available fundamental stretch-mode frequencies. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471956
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 8
    Electronic Resource
    Electronic Resource
    Møller–Plesset perturbation theory applied to vibrational problems (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 11261-11267 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Møller–Plesset perturbation theory is employed to improve the accuracy of static mean field computations in molecular vibration problems. This method is a simple and efficient way to get nearly exact frequencies for few-mode model potentials. For more realistic potentials representing the dynamics of water and formaldehyde, the Møller–Plesset treatment works equally as well. However, we find in general that MP2 level corrections give very accurate energies and additional corrections by higher level terms in the MP series are not substantial. Moreover, we find that for reference states on high energy manifolds degeneracies can result when higher level terms are included in the series. We discuss several ways to remove these degeneracies. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472922
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 9
    Electronic Resource
    Electronic Resource
    Mixed quantum/classical simulation of the photolysis of HCl on MgO(001) (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 11347-11356 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Quantum and mixed quantum/classical calculations of the photolysis of a HCl adsorbate on a MgO surface are reported. In the quantum calculation of the hydrogen dynamics (with rigid surface and chlorine atoms) a strong oscillatory structure is found in the angular distribution of the photofragmented hydrogen as well as in the absorption spectrum. These resonances are caused by temporary trapping of the hydrogen atom between the chlorine atom and the surface and reflect the initial perpendicular adsorption geometry. Corrugation of the surface potential leads to a significant modification of these interference patterns, which exist even for a flat surface. Within a mixed quantum/classical time-dependent self-consistent field (Q/C TDSCF) propagation the influence of surface degrees of freedom on the interference patterns is investigated. The thermal motion of the surface and inelastic collisions of the hydrogen atom with the surface and the chlorine atom washes out most of the oscillatory structure. In the fully angular and energy resolved spectra nevertheless clearly distinguishable peaks are seen. They can be used in practice to extract information about adsorption geometry and surface potential parameters. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472924
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 10
    Electronic Resource
    Electronic Resource
    Nonadiabatic dynamics and electronic energy relaxation of Cl(2P) atoms in solid Ar (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 4626-4635 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The dynamics of Cl(2P) atoms in a solid Ar matrix is studied, with emphasis on electronic energy relaxation of excited states, and on p-orbital reorientation effects. The method used follows Tully's approach for nonadiabatic molecular dynamics simulations, which treats the electronic degrees of freedom quantum-mechanically, and the atomic motions classically, allowing for "hopping'' of the atoms between different potential energy surfaces. We introduce an extended version of this method, to handle "Berry Phase'' effects due to the doubly degenerate Kramers pairs of states present in this system. The role of both electrostatic and of spin–orbit interactions between different electronic states is incorporated in the treatment. The simulations yield a time scale of 13 ps for the energy relaxation of the highest excited electronic state of Cl(2P). A time scale of similar magnitude is found for the depolarization of this state. However, the time scale for orbital reorientation at thermal conditions is only 0.7 ps. This is attributed to the fact that at thermal conditions, only the two lowest electronic states are populated. The physical mechanisms of these basic radiationless decay processes are discussed on the basis of the simulations. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472305
    Library Location Call Number Volume/Issue/Year 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...