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  • 1
    Electronic Resource
    Electronic Resource
    Vibronic structure in the multiple state fluorescence spectrum of C70: A theoretical investigation (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 9675-9684 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The vibronic structure of the fluorescence spectrum of C70 is analyzed on the basis of semi-empirical quantum-chemical calculations followed by modeling of the spectra. Excitation energies of the lowest electronic states of C70 and transition dipole moments are computed with the semi-empirical complete neglect of differential overlap/spectroscopic parametrization (CNDO/S) Hamiltonian combined with configuration interaction calculations which include single and double excitations. Vibronic interactions required to model the structure of the spectra are computed at the same level of theory and the emission spectra of the lowest dipole-forbidden and dipole-allowed excited states of C70 are simulated on the basis of a perturbative expansion of vibronic wavefunctions. The comparison between simulated and observed luminescence spectra indicates that the lowest state responsible for the observed emission is a dipole-forbidden A2′ state which borrows intensity mainly from the lowest two dipole-allowed states of E1′ symmetry. The weakly allowed 1 E1′ state, lying slightly above S1, whose simulated emission shows almost negligible vibronic activity, is assigned to the second emitting state which contributes to the multiple state emission observed for C70. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.476443
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  • 2
    Electronic Resource
    Electronic Resource
    Theoretical analysis of the vibronic structure of the zero-kinetic-energy photoelectron spectra from single vibronic levels of the S1-state manifold of naphthalene (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 4827-4843 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The two-color zero-kinetic-energy (ZEKE) photoelectron spectra of naphthalene are simulated and analyzed by means of quantum-chemical calculations of molecular parameters followed by the modeling of vibronic intensities. Ab initio and semiempirical calculations are carried out to obtain molecular structures of the initial S1 and final D0 states of neutral and ionic naphthalene, respectively. The vibronic perturbations that couple these states to low-lying excited states are also evaluated and included in the model based on the perturbative expansion of vibronic states. It is shown that the simulated intensities reproduce the observed spectra in a very satisfactory fashion. The most prominent bands are identified and some reassignments of ground state frequencies of the cation are indicated on the basis of simulated vibronic intensities. This is, to date, the first completely theoretical simulation of ZEKE spectra of a medium-large molecule based on a model which goes beyond the usually assumed Franck-Condon selection rules. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.474846
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  • 3
    Electronic Resource
    Electronic Resource
    The T1 resonance Raman spectra of 1,3,5-hexatriene and its deuterated isotopomers: An ab initio re-investigation (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 2412-2419 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report a quantum-chemical study of the resonance Raman spectra of the lowest triplet state of 1,3,5-hexatriene. Optimized structures in T1 and in the state (Tn) in resonance with the excitation wavelength are obtained at the ab initio CASSCF level of theory. Vibrational force fields of the E-, Z- and P-rotamers in the lowest triplet state are evaluated and the displacement parameters that govern the activity of totally symmetric modes are derived. The vibrational structure of the RR spectra is modelled for d0-hexatriene and four deuterated isotopomers. Comparison of simulated and observed spectra shows that the activity of the E-isomer of hexatriene accounts very satisfactorily for the observed bands. The contribution of the Z-form is shown to be negligible in agreement with its population in T1. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469664
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  • 4
    Electronic Resource
    Electronic Resource
    Vibronic structure of the emission spectra from single vibronic levels of the S1 manifold in naphthalene: Theoretical simulation (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 3486-3500 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The vibrational structure of electronic spectra of naphthalene is simulated by means of a perturbative calculation of the intensities, based on the vibronic basis set. The formalism is implemented to include the contribution of Herzberg–Teller induced activity for totally symmetric modes and to describe the interference between the latter and the allowed Franck–Condon intensity. Geometries, vibrational normal modes, and vibronic coupling parameters required to model the spectra are obtained by means of ab initio and semiempirical calculations. The structure of absorption and single vibronic level fluorescence spectra is reproduced in detail and consistently for all the spectra examined. It is shown that the intensity of modes ν8a and ν5a is strongly affected by interference effects, and that Dushinsky mode mixing of totally symmetric modes plays a major role in redistributing the intensity among the vibronic bands of the spectra. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471054
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  • 5
    Electronic Resource
    Electronic Resource
    The resonance Raman spectrum of cyclobutene (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 5911-5918 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The vibronic pattern of the resonance Raman spectrum of cyclobutene is simulated by ab initio molecular orbital and by density functional theory calculations. Both Franck–Condon and Herzberg–Teller contributions are included in the analysis of the spectrum. The results suggest an initial dynamics of cyclobutene in the S1 excited state in which the molecule attempts a cis–trans isomerization of the ethylene moiety. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470471
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  • 6
    Electronic Resource
    Electronic Resource
    On the vibronic structure of the absorption spectra of radical cations of some polycyclic aromatic hydrocarbons (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 1387-1399 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The vibronic structure of electronic absorption spectra of four polyacenic radical cations is investigated by means of quantum chemical calculations. We use the semiempirical quantum consistent force field/π electron method (QCFF/PI) augmented by a configuration interaction (CI) scheme that includes all excited configurations having at most one electron in the originally empty molecular orbitals and the ab initio restricted open shell Hartree–Fock (ROHF) method. Displacement parameters for the totally symmetric modes are calculated for different electronic transitions and the resulting Franck–Condon structure is compared with the experimental spectra. The analysis reaffirms the initial interpretation of the absorption spectrum of the cation of naphthalene and reinterprets the recently observed spectrum of the cation of anthracene. First ever analysis of the absorption spectrum of the radical cation of pyrene and perylene is given. For the former, we demonstrate that the unusually large frequency value of the highest ag mode active in the strong absorption band of astronomical interest (443.8 nm) is due to vibronic coupling. For the latter, a resonance vibronic coupling mechanism between manifolds of the 1 2B3g and 1 2B2g states is suggested to explain the doublet structure of the origin of the transition to the latter state.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.466617
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  • 7
    Electronic Resource
    Electronic Resource
    The effect of substituents on the vibronic structure of the electronic spectra of α,ω-dithienylpolyenes: A computational study (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 1298-1311 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present a quantum chemical investigation of the vibronic structure in the electronic spectra of three α,ω-dithienylpolyenes. Equilibrium structures and vibrational force fields of ground and excited electronic states are computed at semiempirical and ab initio levels of theory. The molecular parameters are employed to calculate displacement parameters for totally symmetric modes which are then used to model the vibronic structure of emission and absorption spectra. The observed spectral features are well reproduced by the computed spectra and two characteristic frequency regions are identified for the emission spectra. The first, above 1500 cm−1, is due to the C(Double Bond)C stretching activity typical of trans polyenes. In addition, the strong activity in emission around 1430 cm−1 is rationalized by considering that the two etherocyclic rings add, to the central polyenic chain, a conjugated carbon skeleton with cis linkages. In analogy with the oligomers of thiophene, the cis linkages, along with vibronic coupling, are responsible for the remarkable activity observed in emission in this frequency region. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1381576
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  • 8
    Electronic Resource
    Electronic Resource
    On the vibronic structure of the S0↔S1 transitions in azulene (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 4318-4326 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The semiempirical (quantum chemical consistent force field/π-electron and complete neglect of differential overlap/spectroscopic parametrization) and ab initio methods are used to study the vibronic structure of the optical transitions between the S0 and S1 states of azulene. It is shown that although the excited state is described quite well as arising from the promotion of one electron from the highest occupied molecular orbital to the lowest unoccupied one, the inclusion of doubly excited configurations in description of the wave functions of the two states in question is essential for a proper characterization of the geometry change upon electronic excitation and, therefore, for the resulting Franck–Condon structure of the absorption and emission spectra. The vibronically induced intensities of the b2 fundamentals in the two spectra are calculated and compared with the experimental data, and the problem of correlation between the b2 modes in the two states is solved.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.466085
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  • 9
    Electronic Resource
    Electronic Resource
    Franck–Condon analysis of the S0→T1 absorption and phosphorescence spectra of biphenyl and bridged derivatives (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 7124-7136 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The equilibrium geometry and the vibrational force field of the ground and the lowest triplet electronic states of biphenyl and three bridged derivatives−biphenylene, fluorene and phenanthrene−are computed by using an updated version of the QCFF/PI (Quantum Chemical Force Field/π electron) Hamiltonian. The displacement parameters between T1 and S0 are obtained and used to model the S0→T1 absorption and the phosphorescence spectra. The calculated Franck–Condon envelopes are found to be in excellent agreement with the vibrational structure of the observed spectra. The common features of the phosphorescence spectra of biphenyl and fluorene are related to the same orbital nature of the lowest triplet state. The observed asymmetry between the phosphorescence and singlet–triplet absorption spectra of biphenyl is reproduced when the twisted equilibrium geometry of S0 is considered. It is shown that evidence of the nonplanarity of the ground state of biphenyl is manifested by the lower intensity of the band observed in the phosphorescence at 747 cm−1 with respect to the intensity of the same band in fluorene. The increased vibrational activity calculated in the lower frequency region for biphenylene and phenanthrene agrees with the observed spectra and reflects the different orbital nature of the lowest triplet state of the two strongly perturbed bridged derivatives with respect to biphenyl and fluorene. From the analysis of the computed vibrational frequencies, it is suggested that the false origin of the symmetry forbidden phosphorescence of biphenylene is due to the lowest out-of-plane mode of au symmetry.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463537
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  • 10
    Electronic Resource
    Electronic Resource
    Quantum chemical and vibronic analysis of the 1 2B2↔1 2A2, 2 2B2 transition in benzyl-h7 and benzyl-d7 radicals (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 600-608 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The QCFF/PI+CI method and the CNDO/S+CI method in the floating atomic orbital basis set are used to study vibronic structure of the 1 2B2↔1 2A2, 2 2B2 transition in benzyl-h7 and benzyl-d7 radicals, arising from the activity of a1 and b1 in-plane modes. It is shown that the 6a10 line has its intensity almost entirely due to the borrowing from the 1 2A2→1 2A2 transition via the 1 2A2–1 2A2 coupling. We demonstrate tha the 1 2A2 and 2 2B2 states are strongly mixed by ν8b and ν6b modes. The unperturbed 1 2A2 state lies ∼850 cm−1 below the unperturbed 2 2B2 state. The coupling depresses strongly the position of the 6b10 level mixing it markedly with the level arising from C–CH2 rock (ν18b in other assignments) fundamental. Three-mode vibronic analysis of the absorption and emission spectrum produces vibronic structure that agrees well with the observed spectra. The adiabatic frequency of the ν14 (b1) mode in the 1 2B2 state is shown to be depressed markedly by vibronically induced mode mixing with ν8b mode due to the 1 2B2–n 2A2 interactions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459507
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