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  • 1
    Electronic Resource
    Electronic Resource
    Effect of solvent-induced line broadening on resonance Raman excitation profiles and depolarization ratios (1982)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 86 (1982), S. 4718-4725 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100221a016
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  • 2
    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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  • 3
    Electronic Resource
    Electronic Resource
    Inversion potentials in the ground and excited electronic states of 9,10-dihydroanthracene as probed by the absorption and fluorescence spectra of jet-cooled molecules (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 3511-3516 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The inversion potentials in the ground and the lowest excited singlet states of 9,10-dihydroanthracene were deduced from the fit of the absorption and fluorescence spectra of jet-cooled molecules to model potentials. The barrier height in the ground state (615 cm−1 ) is substantially larger than in the excited state (80 cm−1 ). Correspondingly, the folding angle in the ground state is smaller (144.6° vs 164.1°). Comparison of the calculated line intensities with the experimental absorption spectrum indicates that the transition dipole moment is dependent on the nuclear coordinate of the inversion mode. The measured quantum yield of the single vibronic level fluorescence is essentially independent of the quantum number and the symmetry of the inversion level excited.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459772
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  • 4
    Electronic Resource
    Electronic Resource
    Theoretical study of the force fields of the three lowest singlet electronic states of linear polyenes (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 3681-3688 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The potential energy surfaces of all trans hexatriene and octatetraene are investigated within the harmonic approximation in the diabatic and adiabatic representations for the 1A−g, 2A−g, and 1B+u electronic states by an extended Pople–Pariser–Parr (PPP/CI) model. The effect of excitation and of vibronic coupling on the molecular force fields of the three states is examined. While electronic excitation affects only diagonal force constants of local oscillators, vibronic coupling changes drastically the couplings between local oscillators. The calculations reproduce well the observed increase of the frequency of the in-phase ag C=C stretch upon excitation to the 2A−g state.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454888
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  • 5
    Electronic Resource
    Electronic Resource
    Vibrational potentials of the low frequency out-of-plane motion in the ground and excited singlet electronic states of 9,10-dihydrophenanthrene (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 7229-7236 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The absorption and single vibronic level fluorescence spectra of jet cooled 9,10-dihydrophenanthrene possesses long progressions of a low-frequency vibration identified as the out-of-plane nontotally symmetric CH2–CH2 bridge deformation. The intensity distribution in the observed progressions indicate that the molecule is nonplanar in the ground and the first two excited singlet electronic states described as the plus and minus combinations of the Lb states of the two perturbed benzene rings. The barrier height between the two equivalent nonplanar configurations, with the planar configuration being the transition state, is 2640 cm−1 in S0 and 1430 cm−1 in S1. These values are much larger than those in 9,10-dihydroanthracene. The observed intensity distributions are reproduced well by model calculations with double minimum potentials whose parameters are in good agreement with those obtained by geometry optimization and force field and vibrational frequency calculations by the quantum chemical force field π-electron method. The analysis yields the following values for the angle between the average planes of the two benzene rings: 18.4° in S0 and 12.1° in S1. It is shown that the origin of the S0→S2 transition lies ca. 240 cm−1 above the origin of the S0→S1 transition and that its doublet structure results from a near resonance vibronic interaction between the S1 and S2 states via a b mode of the calculated frequency of 221 cm−1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462427
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  • 6
    Electronic Resource
    Electronic Resource
    Resonance Raman scattering of butadiene: Vibronic activity of a bu mode demonstrates the presence of a 1Ag symmetry excited electronic state at low energy (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 7204-7211 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Resonance Raman spectra of buta-1,3-diene-d0 and buta-1,3-diene-1,1,4,4-d4 have been obtained with ultraviolet excitation from 239.5 to 199.9 nm. Activity of the first overtone of mode 24, the bu symmetry CCC chain deformation mode, is observed with excitation energy below the origin of the 1 1Bu state. This vibronic activity of a nontotally symmetric mode is shown to be evidence of resonance with the 2 1Ag state of butadiene. A quantitative analysis of the ratio of intensities of 2ν24 to ν9, the ag symmetry CCC chain deformation mode, demonstrates that enhancement of 2ν24 cannot be due to resonance with the 1 1Bu state. The resonance enhancement behavior of this overtone band also shows that it is of vibronic origin rather than Franck–Condon allowed. The intensity pattern seen for the modes of bu symmetry is fully consistent with the results of a quantitative calculation of vibronic activity for the eight bu symmetry modes. The 2 1Ag electronic state is estimated to be ca. 0.25 eV below the 1 1Bu electronic state. Overtones of out-of-plane C–H bending and CH2 twisting modes are seen with excitation radiation near the peak of the transition to the 2 1Ag state, indicating that the 2 1Ag state of butadiene has appreciably lower resistance to deformation along out-of-plane coordinates than does the ground electronic state. This is consistent with the expectations of semiempirical calculations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461397
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  • 7
    Electronic Resource
    Electronic Resource
    The missing fluorescence of s-trans butadiene (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 1235-1245 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Geometry of the S0 and S1 states of s-trans butadiene is optimized and the corresponding force fields calculated using a multiconfiguration self-consistent field (MCSCF) method in the complete active space formulation. Three stable conformations of the S1(2Ag) state are shown to be nonplanar (S2, C2, and C1 symmetry), quasidegenerate and separated by a barrier along torsional coordinates of ca. 1600 cm−1. The planar C2h conformation forms a transition state between the S2 and C2 configurations. It is shown by model calculations that the out-of-plane deformation of the S1 state increases dramatically its rate of internal conversion to the ground state. Thus, although the energy gap for the transition is larger in butadiene than that in octatetraene, the internal conversion S1uS0 is estimated to be 3–5 orders of magnitude faster in butadiene. Fast internal conversion in this molecule explains its lack of fluorescence.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459188
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  • 8
    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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  • 9
    Electronic Resource
    Electronic Resource
    Theoretical study of the force field of the lowest singlet electronic states of long polyenes (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 6215-6224 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The force field of all-trans decapentaene, dodecahexaene, tetradecaheptaene, and hexadecaoctaene have been analyzed in the diabatic and adiabatic representations for the 1A−g and 2A−g states by an extended Pariser–Parr–Pople Hamiltonian. The adiabatic frequencies have been computed and found to agree with the existing experimental frequencies. In particular, the calculations reproduce well the observed increase of the frequency of the Franck–Condon active ag C=C stretch upon excitation to the 2A−g state. This mode has been found to be increasingly localized on the CC oscillators of the central moiety as the polyenic chain gets longer. This, together with the alternate signs of the adjacent oscillators, is the reason of its Franck–Condon activity. The effects of electronic excitation and vibronic interactions on the force constant matrix are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457388
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  • 10
    Electronic Resource
    Electronic Resource
    Resonance Raman spectroscopy of the B1u region of benzene: Analysis in terms of pseudo-Jahn–Teller distortion (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 2617-2628 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Raman spectra of benzene and benzene-d6 vapor obtained with excitation in the range from 208 to 188 nm are presented and discussed in terms of vibronic coupling of the resonant B1u state and the nearby E1u electronic state. The Raman spectra show strong activity in the binary overtones and combinations of the e2g modes ν8, ν9, and ν6 with the ν8 activity being dominant. (The Wilson numbering scheme for the modes of vibration is used throughout.) These bands, plus a progression in ν1 alone or in combination transitions involving two quanta of e2g modes, constitute the major intensity bands in the spectra. A simple first-order vibronic coupling model can be constructed which accounts adequately for most of the intensity in the Raman spectra observed in resonance with the B1u state, but this model results in a calculated absorption spectrum that is qualitatively different from that observed. The nature of the discrepancy indicates a significant Duschinsky mode rotation in the B1u state relative to the ground state. An analysis of the vibronic coupling of the B1u state with the nearby E1u state is performed using semiempirical calculation methods to provide excited state geometries, vibrational frequencies, and vibronic coupling parameters.This analysis confirms that there is strong vibronic coupling between these states resulting in a pseudo-Jahn–Teller effect. This results in a highly distorted potential surface for the B1u state with three D2h symmetry antiquinoidal minima lower in energy by ∼1000 cm−1 than the D6h symmetry geometry. The three minima of the threefold symmetric potential surface are separated by local maxima corresponding to the quinoidal geometry with a height of ∼300 cm−1. Three of the four e2g modes are calculated to have significant vibronic activity with mode 8 much stronger than modes 6 or 9. A small Jahn–Teller coupling is calculated. A strong Duschinsky rotation results from the vibronic activity of more than one mode. The absorption spectrum and the resonance Raman spectra calculated from this model are in good agreement with the experimental results. This analysis provides the first evidence for the expected pseudo-Jahn–Teller instability of the isolated 1B1u state of benzene.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462012
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