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  • 1
    Electronic Resource
    Electronic Resource
    Spin–orbit induced radiationless transitions in organometallics: Quantum simulation of the 1E→3A1 intersystem crossing process in HCo(CO)4 (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 905-912 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A theoretical description of the "fast'' (〈50 ps) intersystem crossing processes occurring at critical geometries during the photodissociation of HCo(CO)4 is presented. The radiationless transitions are simulated by wave packet propagations along one-dimensional reaction coordinate on the spin–orbit coupled potential energy surfaces. The propagation are performed separately, either along the Co–H bond or along the Co–COax bond. This original approach has enabled us to understand the mechanism of desactivation of the initially populated singlet excited state in this molecule which should be considered as a model for other organometallics. We propose the following mechanism: (i) in a very short time scale (〈20 fs) 40% of the system dissociates towards the primary products H+Co(CO)4 (1E), whereas the 1E→3A1 intersystem crossing along the Co–H bond elongation occurs within 50 ps; (ii) the dissociation of an axial carbonyl ligand occurs in a larger time scale (200 fs) and only 2% of the system dissociates along the Co–COax elongation. The dominant process is the 1E→3A1 intersystem crossing leading to HCo(CO)4(3A1); (iii) as soon as the lowest triplet state is populated, the system dissociates either to H+Co(CO)4 or to HCo(CO)3+COax on the 3A1 potential energy surface; (iv) the intersystem crossing process may be described as a succession of elementary transitions occurring at critical geometries or crossing points between the singlet and the triplet potential energy surfaces; (v) the efficiency of the radiationless transition is governed by the overlap of the propagated wave packet with the critical region of the coupled potential energy surfaces. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469157
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  • 2
    Electronic Resource
    Electronic Resource
    Spin–orbit coupled excited states in transition metal complexes: A configuration interaction treatment of HCo(CO)4 (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 6591-6596 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A direct spin–orbit coupled configuration interaction method is presented. The basis functions are Slater determinants expressed as combinations of alpha and beta strings. The one and two electron operators are expressed in second quantization form. Spin–orbit coupling is described as a one electron effective operator. The structure of the configuration expansion is single and double excitations from a limited full CI space. Calculations of the Ms=0 component of the three lowest excited states 1,3E and 3A1 in HCo(CO)4 have been performed in order to evaluate the spin–orbit interactions responsible for the 1E→3E and the 1E→3A1 radiationless transitions. A large difference is found in favor of the 1E→3E path.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467068
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  • 3
    Electronic Resource
    Electronic Resource
    Spectroscopy, resolution, and ab initio calculation of vibronic fine structure in the optical absorption of Rh(III) doped in NaCl (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 6849-6857 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A combined spectroscopic and theoretical investigation is devoted to the vibrational fine structure in the broad band spectrum at 4.2 K of the 1T1g and 1T2g states of Rh(III) d6 doped in NaCl. The vibrational structure is resolved with a noise reduction technique using quadrature mirror filters. A weak signal at 16805 cm−1 is identified as the zero phonon line of the 1T1g←1A1g transition, 194 cm−1 below a false origin of a progression in a single 264 cm−1 mode. The observed spectrum can be reproduced quantitatively by ab initio calculations involving identification of the Jahn-Teller active distortions, derivation of the shapes of excited state potential energy surfaces, and calculation of the Franck–Condon factors. The dominant mode of the progression is identified as a combination of the a1g and eg(a) modes with a calculated frequency of 279 cm−1. The calculations further reveal the existence of a conical intersection between the 1T1g and 1T2g states, situated in the optical window between the two absorption bands and expected to play an important role in the deactivation of the 1T2g state. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478590
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  • 4
    Electronic Resource
    Electronic Resource
    Spin-orbit induced radiationless transitions in organometallics: Quantum simulation of the intersystem crossing processes in the photodissociation of HCo(CO)4 (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 1421-1428 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A theoretical description of the "fast" (〈50 ps) intersystem crossing (ISC) processes occurring during the photodissociation of HCo(CO)4 is presented. The radiationless transitions are simulated by wave packet propagations on spin-orbit coupled two-dimensional potential energy surfaces (CASSCF/CCI) calculated along two reaction coordinates (qa=[Co–H] and qb=[Co–COax]). A mechanism of deactivation of the singlet excited state of HCo(CO)4 initially populated on UV excitation has been proposed. This mechanism differs slightly from the one deduced from a one-dimensional simulation performed separately, either along the Co–H bond or along the Co–COax bond: (i) in a very short time scale (〈20 fs) 35% of the system dissociates toward the primary products H+Co(CO)4 (1E), whereas the 1E→3A1 and 1E→3E intersystem crossings occur within 50 ps; (ii) as soon as the lowest triplet states are populated, the system dissociates either to H+Co(CO)4 (3A1) or to H+Co(CO)4 (3E) on the corresponding potential energy surfaces; (iii) the indirect photodissociation mechanism through ISC may be described as a succession of elementary transitions followed by the homolysis of the metal–hydrogen bond. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.473291
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  • 5
    Electronic Resource
    Electronic Resource
    Molecular dynamics simulation of the zero-field splitting fluctuations in aqueous Ni(II) (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 1800-1811 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The fluctuations in the zero-field splitting (ZFS) of the electronic ground state of the Ni(II) ion in aqueous solution have been studied through a combination of ab initio quantum chemistry calculations, including spin–orbit coupling, and molecular dynamics (MD) simulations. The ab initio calculations for the hexa-aquo Ni(II) complex have been used to generate an expression for the ZFS as a function of the distortions of the idealized Th symmetry of the complex along the normal modes of Eg and T2g symmetries. The MD simulations provide a 200 ps trajectory of motions in the system consisting of a Ni(II) ion and 255 water molecules, which is analyzed in detail in terms of both the structure and the dynamics in the solvation sphere around the ion. The time correlation function (TCF) for the ZFS interaction has been computed and analyzed. It is found that the mean square amplitude of the ZFS is about 5.2 cm−1, which is about twice the estimates based on the model-dependent analysis of the proton spin relaxation in the aqueous Ni(II) solution. The decay of the ZFS TCF is found to occur on a subpicosecond time scale, which is much faster than earlier proposals. It is also interesting to note, for comparison with theoretical models, that the ZFS tensor is far from cylindrical and that the normal modes of Eg och T2g symmetry both contribute to its fluctuations. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469754
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  • 6
    Electronic Resource
    Electronic Resource
    The optical absorption spectrum of the octahedral RhCl63− complex: Ab initio calculations of excitation energies and the effect of spin-orbit coupling (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 3145-3152 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The spin-orbit states of octahedral RhCl63− in the three lattices NaCl, Cs2NaYCl6 and water solution have been investigated theoretically with multiconfigurational self-consistent field (SCF) type procedure (CASSCF), followed by a second order perturbation correlation treatment (CASPT2). The spin-orbit effects for the ground state 1A1g and the lowest excited states 3T1g, 3T2g, 1T1g and 1T2g were calculated with an effective one-electron operator and shifts of more than 1000 cm−1 were found. Different basis sets were tried: the presence of f functions on Rh and d functions on Cl is important for both excitation energies and equilibrium distances. There is agreement between computed excitation energies and the available experimental data that indicate a redshift of the 1T1g,2g← 1A1g transitions as the Rh–Cl distance increases. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.476906
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  • 7
    Electronic Resource
    Electronic Resource
    Spin dynamics under the Hamiltonian varying with time in discrete steps: Molecular dynamics-based simulation of electron and nuclear spin relaxation in aqueous nickel(II) (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 3181-3188 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A method of calculating the time correlation functions for electron spin is proposed, based on solving the time-dependent Schrödinger equation for a spin Hamiltonian that contains a term varying randomly in discrete time steps. It is applied to the study of electron spin relaxation in aqueous solution of nickel(II) ions with S=1. The random term in the spin Hamiltonian in this case is the zero-field splitting (ZFS) interaction. The method is evaluated by an application to a model system (the pseudorotation model) for which an analytical solution to the electron spin relaxation problem is known. The same method is then employed to study the electron and nuclear spin dynamics in a system where the time variation of the zero-field splitting is obtained by a combination of ab initio quantum chemistry and molecular dynamics simulations. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471083
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  • 8
    Electronic Resource
    Electronic Resource
    Infrared properties of diabase glass and wool (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 5024-5030 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Results from infrared reflectance and collimated transmittance of a diabase glass are presented and compared with data for wool, prepared from the same glass. Using very thin glass slices it proved possible to establish a lower limit to the extinction coefficient k (1200 cm−1)≥0.043 where the glass exhibits a low reflectance minimum and the wool transmittance a sharp maximum, related, but not identical to, the classical Christiansen effect. With this low limit to the extinction coefficient of the glass material, a fivefold transmittance enhancement of the wool in comparison to glass is confirmed. As a tentative explanation it is suggested that the rapid quenching of the glass fibers causes a reduction of the k value. It is also demonstrated that the wool transmittance maximum at 1200 cm−1 decreases exponentially with sample thickness, significantly faster than a secondary maximum at 2240 cm−1. Dispersion analysis of the bulk glass reflectance was performed using four Lorentz oscillator terms. The resonance frequencies obtained from the dispersion analysis can be related to the vibration modes of the sodium-silicate glasses, considering the presence of both network-forming and modifying impurities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.343176
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  • 9
    Electronic Resource
    Electronic Resource
    Simple nonempirical calculations of the zero-field splitting in transition metal systems: I. The Ni(II)-Water complexes (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 295-309 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A simple nonempirical scheme is presented for calculating the splittings of ground state multiplets (the zero-field splitting) in transition metal complexes. The method employs single reference, single excitation CI calculations based on open-shell RHF. The spin-orbit coupling is described using an effective one-electron, one-center operators. The method is applied to the triplet state Ni(II) complexes with one to six water molecules. The validity of the second-order perturbation theory approach and of the spin-Hamiltonian formalism is found to be limited to slightly distorted octahedral systems. Generally, small changes in the geometries of the complexes are found to cause substantial variations of the splitting pattern.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560382430
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