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  • 1
    Electronic Resource
    Electronic Resource
    Formation and dissociation of negative ion resonances in methanol and allylalcohol (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 7453-7458 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Dissociative electron attachment by methanol, different deuterated methanols, and allylalcohol is studied including an analysis of the translational excess energy release of the ionic fragments. Although the energetic threshold for negative ion formation (OH−, O−) is near 2 eV, these ions are generated in methanol only within a prominent resonance at 10.5 eV. OH− and OD− formation is characterized by hydrogen scrambling in the temporary parent ion while the formation of CH3O− (and the deuterated analog) proceeds directly (no hydrogen scrambling). Only O− is generated with considerable translational excess energy (1.0±0.2 eV). In contrast to methanol, allylalcohol captures electrons at 1.7 eV to form OH− and the enolate anion (M–H)−. This resonance is interpreted as a Π radical anion comparable to that known in ethylene.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454309
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  • 2
    Electronic Resource
    Electronic Resource
    Low energy (0–10 eV) electron attachment to CF3Cl clusters: Formation of product ions and analysis of excess translational energy (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 357-364 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Electron attachment to CF3Cl clusters has been studied mass spectrometrically in a beam experiment. In addition to the fragments known from dissociative attachment to the isolated compound (F−, Cl−, etc.), a veriety of larger complexes such as M−n, Mn⋅Cl−, Mn⋅F−, n≥1 (M=CF3Cl) could be observed. The resonance profiles of the ion yield curves suggest that the initial step of electron capture proceeds via the formation of a temporary CF3Cl− ion within the target aggregate followed by different decomposition reactions. Among the various products, the parent radical anion (CF3Cl−) is generated in its relaxed configuration not accessible in electron capture by the isolated molecule. A time-of-flight (TOF) analysis of the Cl− products reveals two decay channels, one associated with high excess translational energy and a second releasing the Cl− ion with only thermal energy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459534
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  • 3
    Electronic Resource
    Electronic Resource
    Generalized quantum Fokker–Planck theory and its application to laser driven intramolecular hydrogen transfer reactions in condensed phases (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 6104-6112 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A generalized quantum Fokker–Planck theory is proposed to treat the correlated dynamics of coherent driving and Markovian dissipation. The resulting formulation is applicable to arbitrary external time-dependent driving fields and satisfies the detailed balance condition at arbitrary temperatures. Analyzed are also the formal relations among the Caldeira–Leggett quantum Fokker–Planck equation, the Bloch–Redfield theory, and the present formulation. The approach is numerically implemented to study the intramolecular hydrogen transfer reaction dynamics in a one-dimensional model system. Different forms of external pulsed driving fields are exploited and their ability to compete with concurring relaxation processes is investigated. Energy relaxation and pure dephasing are shown to have rather different influences on the reaction yield. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481212
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  • 4
    Electronic Resource
    Electronic Resource
    The direct production of CO(v=1–9) in the reaction of O(3P) with the ethyl radical (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 4572-4580 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A new product channel that yields vibrationally excited CO(v=1–9) in the reaction of the ethyl radical with O(3P) is experimentally observed by time-resolved Fourier transform infrared emission spectroscopy. The branching ratios for the different vibrational states are estimated to be 0.21±0.06, 0.27±0.03, 0.14±0.02, 0.08±0.02, 0.07±0.02, 0.07±0.02, 0.06±0.02, 0.05±0.02, and 0.05±0.02 for v=1–9, respectively. Previously, only the CH3+H2CO, CH3CHO+H, and C2H4+OH channels were known. Kinetics tests are provided to verify that the CO is produced directly in the reaction and not from secondary chemistry. The two possible new product channels are CO+CH4+H and CO+CH3+H2. The implications of this previously unexplored reaction channel for combustion chemistry and the possible mechanisms for this reaction are discussed. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1288791
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  • 5
    Electronic Resource
    Electronic Resource
    Coherent and dissipative wave packet dynamics in cyclic model systems with four equivalent potential minima (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 9007-9017 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The dynamics of cyclic systems with four equivalent potential minima is studied here from two different points of view. The solution of the time-dependent Schrödinger equation provides insight into the coherent wave packet motion. The resulting reaction mechanism involves relocalization between opposite, not neighboring potential minima. The inclusion of an environment within a density matrix description leads to dissipation and therefore to a transition from coherent to incoherent dynamics. The theoretical considerations are applied to a simple model of the cyclic motion of a proton in a molecular framework.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.466705
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  • 6
    Electronic Resource
    Electronic Resource
    Dissipative vibrational dynamics in a curve–crossing system (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 10404-10415 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The density matrix theory is utilized for the description of ultra fast optical properties and related vibrational wave packet dynamics of molecular systems in condensed media. As an example, optically induced vibrational wave packets in the so-called curve–crossing system are considered. Such a system goes beyond the standard treatment of optical phenomena since the vibrational wave packet moves in a double well potential and is subject to environmental influences like wave function dephasing and relaxation. The complete theoretical description has been carried out in a representation of the vibrational wave functions of the diabatic states which refer to the two coupled vibrational surfaces. Solving the corresponding density matrix equations by numerical methods allows us to incorporate the static coupling between the crossed surfaces in a nonperturbative manner. Standard projection operator technique is used to treat environmental contributions up to the second order. For the case of a bilinear coupling between the molecular system and the environment we determine the time development of an initially prepared Gaussian wave packet. Corresponding time-resolved spectra of a pump–probe configuration are also derived. The developed formalism is finally applied to the system of the coupled electronic states c' 1Σ+u and b' 1Σ+u of the N2 molecule. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467921
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  • 7
    Electronic Resource
    Electronic Resource
    Laser driven ground state photodissociation of HCo(CO)4: An ab initio quantum molecular dynamics approach (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 94-100 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The competition between laser selective dissociation of the axial Co–CO bond and intramolecular energy redistribution in HCo(CO)4 is investigated. Our approach is based on an ab initio calculation of the Cartesian reaction surface Hamiltonian along the Co–CO bond distance using density functional theory. The substrate degrees of freedom are treated within the harmonic approximation. We find only two modes which are strongly coupled to the dissociation reaction, one which can be approximately described as an H–Co stretching vibration while the second one is an umbrella type vibration of the equatorial carbonyls. The region of validity for harmonic motion of the substrate normal modes is explored. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480564
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  • 8
    Electronic Resource
    Electronic Resource
    Effective bridge spectral density for long-range biological energy and charge transfer (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 5821-5833 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The role of medium-induced relaxation of intermediate (bridge) sites in energy and charge transfer processes in molecular aggregates of arbitrary size and geometry is explored by means of Green's function techniques. The coupling of electronic and (solvent and intramolecular) nuclear degrees of freedom is incorporated using the Brownian oscillator model, which allows an exact calculation of the necessary two-point and four-point correlation functions of exciton operators. The signatures of energy transfer and spectral diffusion in time- and frequency-resolved fluorescence spectroscopy are studied. A unified expression for the frequency-dependent transfer rate is derived, which interpolates between the sequential and superexchange limits. Numerical results and a Liouville space pathway analysis for a donor–acceptor system coupled through a single bridge molecule are presented. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471393
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  • 9
    Electronic Resource
    Electronic Resource
    Two-exciton spectroscopy of photosynthetic antenna complexes: Collective oscillator analysis (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 8586-8601 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The linear and third-order polarizabilities of the light-harvesting antennae of photosynthetic bacteria and green plants are calculated using an equation of motion approach which maps the system onto a coupled set of anharmonic excitonic oscillators. The oscillator representation is shown to have several advantages over the traditional picture based on properties of individual global eigenstates of the aggregate; besides a considerable reduction of computational effort, the dynamics of excitations in the two-exciton band is conveniently analyzed in terms of single-exciton Green's functions and the two-exciton scattering matrix. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472642
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  • 10
    Electronic Resource
    Electronic Resource
    Pump–probe spectroscopy of dissipative energy transfer dynamics in photosynthetic antenna complexes: A density matrix approach (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 4154-4164 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The photoinduced ultrafast dynamics of singlet excitons in light-harvesting antennae is investigated using multilevel Redfield theory. Formulating the equations of motion for the reduced exciton density operator in terms of one- and two-exciton eigenstates we focus attention on the influence of dynamic exciton-vibrational coupling and static diagonal disorder on transient absorption spectra of peripheral antennae in photosynthetic purple bacteria. The simulations are discussed in view of recent experimental results obtained for the B850 absorption band of Rhodobacter sphaeroides. Further, we suggest a new way of estimating the size of the exciton coherence domain in these systems which puts emphasis on the dynamic character of exciton localization. For the B850 pigment pool we find that at room temperature the pump–pulse initially prepares a coherent superposition of one-exciton eigenstates which can be delocalized over the whole aggregate. With increasing delay time the exciton coherence domain shrinks to cover about four pigments in the asymptotic limit. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.474803
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