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  • 1
    Electronic Resource
    Electronic Resource
    Analysis of vibronic-mode coupling in azulene by fully resonant coherent four wave mixing (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 2205-2216 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Fully resonant, three laser, coherent Stokes Raman scattering (CSRS) is used to probe the vibrational correlations and couplings associated with the S0−S1 transition of azulene in a low temperature mixed molecular crystal. Unlike incoherent resonant emission, CSRS is not complicated by extra resonances due to relaxed emission. The spectra obtained confirm most of the assignments of the S1 vibronic fundamentals made by incoherent spectroscopies. In addition, however, the vibronic counterpart of the vibrational fundamental at 900 cm−1 is correlated to a previously unobserved vibronic resonance at 842.3 cm−1. Evidence of matrix moderated coupling, including possible site splitting and Fermi resonances involving lattice phonons, is given for the 677, 825, 917, 941, and 900 cm−1 vibrational levels.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459053
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  • 2
    Electronic Resource
    Electronic Resource
    Analysis of vibrational correlations and couplings in the lowest two singlet states of pentacene by high resolution, fully resonant, coherent four-wave mixing spectroscopy (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 5186-5195 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Coherent, fully resonant four-wave mixing (FRFWM) spectroscopy is used to probe the vibrational and vibronic state of the pentacene S0 and S1 electronic states. High resolution is obtained using mixed molecular crystals at cryogenic temperatures. The FRFWM spectra combined with conventional absorption and fluorescence spectra allow correlation of the S1 fundamentals to the corresponding ground state normal coordinates. Couplings between modes are indicated and may be related to Fermi resonance of the pentacene vibrations by means of host librational phonons.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458553
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  • 3
    Electronic Resource
    Electronic Resource
    Analysis of vibronic mode coupling in pentacene by fully resonant coherent four-wave mixing (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 1538-1546 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: This paper develops the theoretical framework for the analysis of relative peak intensities in fully resonant, three laser, coherent four-wave mixing spectra of molecular vibrational and vibronic levels. For a Franck–Condon system, the relative vibronic peak intensities are shown to scale as the square of the absorption spectrum for all resonances not associated with the normal mode selected by the fixed vibrational resonance. A large enhancement of vibronic resonances involving the selected mode is predicted for typical potential well offsets. Higher order mode coupling causes deviations from these predictions by allowing other coupled resonances to be enhanced as well. Vibrational peak intensities are similarly related to the emission spectrum. Pentacene in benzoic acid mixed crystals at 2 K are used to experimentally study the mode mixing effects. It is shown that important coupling occurs between the 747.7 and 790.8 cm−1 vibronic modes of the pentacene S1 electronic state. Two possible mechanisms for this coupling are suggested. This work shows that the relative intensities of vibrational and vibronic resonances in fully resonant four-wave mixing spectra can serve as a useful probe of mode coupling.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458084
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  • 4
    Electronic Resource
    Electronic Resource
    Vibronic spectroscopy of amorphous materials using higher order, multiresonant coherent anti-Stokes Raman spectroscopya) (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 3940-3949 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Multiresonant coherent anti-Stokes Raman spectroscopy is performed with three tunable lasers on perylene doped polymethylmethacrylate (PMMA). Sharp vibronic features can be observed in vibronic scans at constant energy from the parent electronic transition when resonance is established within the inhomogeneously broadened electronic band. These features are attributed to the nonlinear line narrowing predicted by Ouellette and Denariez-Roberge for a higher order saturated coherent anti-Stokes Raman process since line narrowing should be absent for four wave mixing coherent anti-Stokes Raman spectroscopy. It is shown that the features are sharply dependent on the presence of a simultaneous vibrational resonance as is also predicted by the higher order coherent anti-Stokes Raman model. Excited state coherent anti-Stokes Raman spectroscopy with resonance enhancement from higher singlet states does not contribute to the narrow features since such a process would not have vibrational resonances. Conventional two laser coherent anti-Stokes Raman shows only a weak line at the vibronic transition.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462933
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  • 5
    Electronic Resource
    Electronic Resource
    Nonlinear line narrowing of excited state resonances in perylene doped poly(methylmethacrylate) using multiply enhanced nonparametric spectroscopy (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 1479-1486 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Line narrowing of perylene vibronic transitions in poly(methylmethacrylate) (PMMA) samples has been demonstrated using multiply enhanced nonparametric spectroscopy. Three lasers are used to generate a four wave mixing signal that is resonantly enhanced by three simultaneous perylene resonances involving a vibrational state, a vibrationless excited electronic state, and a vibronic state of the excited electronic state. There is a correlation between the position of the electronic and vibronic states within the inhomogeneously broadened absorption spectrum. The correlation can be used to achieve line narrowing by fixing one of the resonances to a subset of perylene sites within the inhomogeneous profile so the other resonance of those sites will be selectively enhanced. The position of the line narrowed vibronic peaks depends upon the electronic detuning from the center of the inhomogeneously broadened absorption band as different sites within the band are probed. Excited state coherent processes involving resonance with higher singlet states are shown to be unimportant from the detuning dependence on a simultaneous vibrational enhancement.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461063
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  • 6
    Electronic Resource
    Electronic Resource
    Multiresonant four-wave mixing in diphenyloctatetraene doped bibenzyl crystals (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 1274-1283 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A diphenyloctatetraene (DPOT) doped bibenzyl crystal is a model system for studying the spectroscopic properties of polyenes because the well-defined local environment of the DPOT eliminates most of the inhomogeneous broadening that obscures many transitions. The spectra of the three DPOT sites in this host are measured with site-selective laser spectroscopy to define the vibrational, electronic, and vibronic states of the S0, S1, and S2 electronic states. Multiply resonant four-wave mixing spectra were then obtained using a coherent anti-Stokes Raman spectroscopy method (CARS) for a series of different laser frequencies in order to define the CARS excitation profile (CEP). The CEP profile of the C=C and C–C stretch vibrations showed strong enhancement of the four-wave mixing from the S2 state but only the C=C stretch mode had observable enhancement from the S1 state. Contrary to previous studies in pentacene, azulene, and perylene, DPOT did not exhibit enhancement of vibronic transitions that would permit mode selective or site-selective nonlinear spectroscopy. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469803
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  • 7
    Electronic Resource
    Electronic Resource
    Spectral line-narrowing and saturation effects in fully resonant nondegenerate four wave mixing (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 2981-2994 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Pentacene doped benzoic acid crystals are used to study the line-narrowing capability of fully resonant four wave mixing for inhomogeneously broadened transitions. Both parametric and nonparametric nonlinear spectroscopies are used to scan the vibronic resonances of excited electronic states while maintaining resonance with a vibrational mode of the ground state and the vibrationless level of the excited state. The observed vibronic transitions correspond to modes that are coupled to the ground state mode. The spectra contain both lines that are narrowed and lines that have the full inhomogeneous width. Narrowing of the vibronic transitions is observed when site selection is performed on the vibrationless electronic transition in both parametric and nonparametric methods. Narrowing of the vibrational resonance is not observed under the same conditions showing that the vibrational and electronic inhomogeneous broadenings are not correlated. The shifts of the line positions and the changes in linewidths and relative intensities were measured across the inhomogeneous linewidth for both methods. The nonlinear signal intensity was also measured as a function of laser intensity. All of the results are consistent with a theoretical description where saturation effects are dominant.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453939
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  • 8
    Electronic Resource
    Electronic Resource
    Laser spectroscopic study of defect equilibria in SrCl2 (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 400-410 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The site distribution of the different charge compensated sites in singly doped samples of SrCl2:Eu3+ and doubly doped samples containing a second rare earth ion has been measured by site selective laser spectroscopy for a range of different dopant concentrations and annealing temperatures. The site distribution exhibits the same anomalous behavior as was observed in alkaline earth halide crystals as long as the dopant levels are not too low. At very low dopant levels, the anomalous behavior is not observed and the dependence follows that expected for simple mass action descriptions of defect equilibria. An association constant is obtained at the low concentrations and it is found that the amount of association is much less than would be expected from theoretical estimates based on Harwell automatic defect evaluation system (HADES) models. Extensive clustering is observed at lower concentrations than in the alkaline earth fluorides. The number of different clusters and the types of clusters do not appear to have a strong dependence on the ionic radius of the dopant ions as would be expected from HADES calculations. The anomalous site distributions at the higher concentrations are attributed to additional interactions between defect structures that result from strain interactions. Since these interactions lead to concentration dependence of the free energy of formation for the different defect sites, it will be necessary to include these effects in models that are used to predict the relative dominance of different sites.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452578
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  • 9
    Electronic Resource
    Electronic Resource
    Singly vibrationally enhanced infrared four wave mixing spectroscopy (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 4112-4122 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We describe a new nonlinear, nonparametric process that provides a direct measure of vibrational enhancement in four wave mixing. This process has 14 coherent pathways that create the final coherence. In the limit of no pure dephasing and a single vibrational resonance, the 14 pathways combine into a single process that is vibrationally enhanced. The frequency and concentration dependence expected for this process matches that observed in experiments with the methyl- and methylene C–H stretch vibrations in hexane samples. The third-order nonlinear susceptibility for the C–H vibrations was measured by the interferometric method of Levenson and Bloembergen. The vibrational nonlinearity was observed as a difference between the nonresonant electronic contributions and the contribution that depended on resonance with the vibrational absorption transition. The measurements show that the vibrational enhancement is 50 times larger than the nonresonant electronic contribution and it shows that spectroscopic methods based on resonant nuclear nonlinear polarizations are observable above the electronic nonlinear polarization background. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.475809
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  • 10
    Electronic Resource
    Electronic Resource
    Infrared spectroscopy of ethanol clusters in ethanol–hexane binary solutions (2002)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 116 (2002), S. 5717-5724 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Temperature and concentration dependent infrared spectra were recorded for binary solutions of ethanol–hexane, ethanol–carbon tetrachloride, and ethanol–cyclopentane. The temperature range covered was 198 K to 298 K; concentrations ranged from 0.45 mole percent to 4.0 mole percent ethanol. Changes in the OH stretch frequency are consistent with the formation of ethanol clusters (EtOH)n, where n ranges from 2 to 6. The geometry, OH stretch frequency and proton chemical shift for 14 different ethanol clusters ranging from monomer to hexamer in cyclic and linear arrangements were investigated using density functional methods (B3LYP/6-31+G*). These clusters include both gauche and anticonformers of the monomer unit. The OH stretch frequency calculations were compared to experimental Fourier transform infrared measurements made as a function of concentration and temperature for dilute ethanol in hexane binary mixtures. Analysis of the O–H stretch frequency data (3100 to 3700 cm−1) indicate the presence of small clusters of ethanol. The data indicate that at the lower temperatures the clusters are primarily cyclic tetramers, pentamers, and hexamers. This infrared data is in excellent agreement with recent concentration and temperature dependent nuclear magnetic resonance chemical shift investigations that indicate a dramatic change in cluster size with concentration and temperature. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1458931
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