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  • 1
    Electronic Resource
    Electronic Resource
    Solvation state selective excitation in resonance Raman spectroscopy. I. Experimental study on the C(Double Bond)N and the C(Double Bond)O stretching modes of phenol blue (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 9075-9083 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have measured the excitation photon energy dependence of the resonance Raman spectra of a solvatochromic dye, phenol blue (PB) in various solvents from nonpolar to dipolar ones, including supercritical fluids of trifluoromethane and carbon dioxide. We have found that the band peak positions of the C(Double Bond)N stretching mode of PB appear to change with the excitation laser frequency in polar solvents. On the other hand, no dependence of the band peak positions on the excitation frequency is found in nonpolar solvents. The peak positions of the C(Double Bond)O stretching mode also show small excitation energy dependence in chloroform and in methanol. The extent of the excitation energy dependence is correlated with the amount of the fluctuation of the local field on PB molecule exerted by the solvent, which had been estimated from the bandwidths of the absorption and the Raman spectra of PB in solution. The IR absorption spectra of PB are measured in chloroform and carbon tetrachloride, and compared with the Raman spectra in the same solvents. The excitation energy dependence is explained by the solvation state selective excitation in the resonance Raman spectroscopy, that is, the inhomogeneity that appears in the absorption spectra of PB also appears in the resonance Raman process. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.477463
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  • 2
    Electronic Resource
    Electronic Resource
    Electron spin resonance studies in β-FeSi2 crystals (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 1678-1681 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The electron spin resonance studies have been carried out in the temperature range 130–300 K on semiconducting β-FeSi2 single crystals grown by a chemical vapor transport technique. Two anisotropic doublets with apparent g factors in the range 2.025–2.05 and 1.98–2.03, as well as one complex signal having an isotropic g factor of 2.0195 and exhibiting a five-line hyperfine structure, have been detected. The doublet signals are believed to arise from spin triplet (S=1) states of, presumably, substitutional Ni2+ transition ions, whereas the signal exhibiting the hyperfine structure has been attributed to the spin of a hole, captured by silicon vacancy and interacting with nuclear spins of four iron atoms in the first shell surrounding of the silicon vacancy. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362967
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  • 3
    Electronic Resource
    Electronic Resource
    Effect of the solvent density and species on the back-electron transfer rate in the hexamethylbenzene/tetracyanoethylene charge-transfer complex (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 1485-1498 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The back-electron transfer (b-ET) process in the hexamethylbenzene/tetracyanoethylene charge-transfer complex was studied by the transient absorption spectroscopy in several fluids (ethane, nitrous oxide, carbon dioxide, and trifluoromethane) from the critical density to twice that of it at 323.2 K. The b-ET rate was determined by the decay rate of the excited state absorption. The b-ET rate increased with the increase of solvent density in carbon dioxide and nitrous oxide. The b-ET rate also increased in the order of ethane, nitrous oxide, carbon dioxide, and trifluoromethane, compared at the similar reduced density divided by the solvent critical density. Based on the formulation by Marcus and Jortner, the reaction free energy and the solvent reorganization energy were estimated from the change of the absorption spectrum relative to the gaseous phase spectrum, simply by assuming that the intramolecular reorganization energy does not depend on the solvent density and the species. The reaction free energy and the solvent reorganization energy in fluids obtained in this way were almost linearly correlated, and the density dependence was larger in the lower density region. The b-ET rates in various conditions showed a good correlation with the reaction free energy estimated from the spectral simulation. The b-ET rate showed a significant isotope effect by perdeuteriation of hexamethylbenzene as is predicted by the fluorescence quantum yield [K. Kulinowski et al., J. Phys. Chem. 99, 17715 (1995)], which could not be reproduced by this model. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.475520
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  • 4
    Electronic Resource
    Electronic Resource
    The excitation energy dependence of the Raman–Stokes shift: The resonance Raman spectra of phenol blue in methanol (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 4436-4438 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We found that the Raman–Stokes shift of the C(Double Bond)N stretching mode of Phenol Blue changes with excitation energy; the frequency of this Raman band increased with an increase of the excitation energy, whereas the bandwidth was almost the same. The origin of the excitation energy dependence is discussed in connection with the correlation of the effect of the solvent fluctuation on the electronic transition energy and the vibrational frequency. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.474785
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  • 5
    Electronic Resource
    Electronic Resource
    The role of the attractive and the repulsive interactions in the nonpolar solvation dynamics in simple fluids from the gas-like to the liquid-like densities (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 4169-4185 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have performed molecular dynamics (MD) simulations of the nonpolar solvation dynamics in simple fluids composed of particles interacting through the Lennard-Jones (LJ) 12–6 potential or its repulsive part. The attractive or the repulsive part of the solute–solvent interaction is assumed to change on the excitation of a solute. We have followed the transition energy fluctuation of the solute by the equilibrium simulation. The division of the LJ potential followed the method of WCA [J. W. Weeks, D. Chandler, and H. C. Andersen, J. Chem. Phys. 54, 5237 (1971)]. We have surveyed over a wide solvent density region from gas-like to liquid-like densities at the constant temperature. When the attractive part changes, the relaxation becomes faster with an increase of the solvent density. This result contradicts with previous theories that treat the nonpolar solvation dynamics in terms of the diffusion of solvent particles. The time scale of the initial part of the relaxation is well correlated with the static fluctuation divided by the static average, which suggests the importance of the curvature of the free energy surface in the initial part of the solvation. When the repulsive part changes, the initial part of the relaxation is almost density independent, determined by the binary motion between solute and solvent. It is consistent with the result that the static fluctuation is almost proportional to the static average, which indicates the absence of the static correlation between solvent particles. On the other hand, the solvation correlation function shows rather complicated density dependence at the longer time scale. In the case of the binary mixture solvent, the relaxation time is inversely proportional to the diffusion coefficient. On the basis of the nonpolar solvation dynamics, the validity of the isolated binary collision model for the vibrational energy relaxation is also discussed, and the recent hydrodynamic theory on the vibrational energy relaxation [B. J. Cherayil and M. D. Feyer, J. Chem. Phys. 107, 7642 (1997)] is critically examined. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479715
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  • 6
    Electronic Resource
    Electronic Resource
    Effect of solvent density and species on static and dynamic fluorescence Stokes shifts of coumarin 153 (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 5474-5484 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Solvent density dependence of the absorption and fluorescence spectra of coumarin 153 in argon (Ar), ethane (C2H6), carbon dioxide (CO2), and trifluoromethane (CF3H) has been studied at 323.2 K over a wide density region up to ρr∼3, where ρr is the reduced density by the critical density (ρc) of the solvent (ρr≡ρ/ρc). By analyzing the line shape functions of the absorption and fluorescence spectra, the first moment and the full width of the half maximum (FWHM) have been determined. Both the free energy difference (ΔG) between the ground and the S1 states and the fluorescence Stokes shift (Δν), evaluated by the first moments of the absorption and fluorescence line shape functions, show larger shift to the values in vapor in the order of Ar, C2H6, CO2, and CF3H if compared at the same ρr. There are three characteristic density regions on the density dependence of ΔG and Δν; these values show larger dependence in the lower-density region (ρr〈0.5) and the higher-density region (ρr〉2), than that in the medium-density region. The solvent density and species dependence of the FWHM of the absorption spectrum is quite similar to that of Δν. The density dependence of Δν and FWHM in Ar and C2H6 indicates that the intramolecular reorganization energy decreases with increasing the solvent density, while the effect is small. We have estimated the solvent reorganization energy (λS) in CO2 and CF3H by assuming no contribution of λS in C2H6 and Ar. We have demonstrated that the dielectric continuum model makes a good prediction on the relation between ΔG and λS, while it is poor on their density dependence. The invariance of ΔG and λS in the medium-density region can be interpreted as the density saturation around the solute molecule. In the lower-density region (ρr〈∼0.5), the way of the solvation is suggested to be different from those in the medium- and high-density regions. The lifetime of S1 shows a large dependence on the solvent density and species in the very low-density region (ρr∼0.05). We have also found that slow solvation dynamics exists in the lower-density region of CF3H. The origin of the dynamics is discussed in relation with the static Stokes shift. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479808
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  • 7
    Electronic Resource
    Electronic Resource
    Solvation state selective excitation in resonance Raman spectroscopy. II. Theoretical calculation (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 9084-9095 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have reported in the previous paper [J. Chem. Phys. 109, 9075 (1998)] that the Raman Stokes shifts of the C(Double Bond)O and the C(Double Bond)N stretching modes in the resonance Raman spectra of a solvatochromic dye, phenol blue (PB), appear to depend on the excitation photon energy in polar or protic solvents. The reason was ascribed to the solvation state selective excitation due to the inhomogeneous distribution of the solvation environment. In this paper we have made a theoretical model calculation to demonstrate that the solvation state selective excitation indeed brings about the excitation energy dependence of the resonance Raman Stokes shift in solution. In our model, both the electronic and the vibrational transitions are linearly coupled to the same harmonic bath, to embody the coupling between the fluctuations of the electronic and the vibrational transition energies. The absorption and the resonance Raman cross sections are formulated for this model on the basis of the time dependent path integral method. In the formulation, the finite relaxation time of the bath mode and the vibrational progressions in the absorption spectra are also taken into account. We have calculated the resonance Raman spectra at various excitation photon energies for the model system probable for PB in methanol. The parameters for the calculation are estimated from the analysis of the absorption and the resonance Raman spectra. It is demonstrated that the Raman Stokes shift indeed depends on the excitation energy for this model. It is noted that the vibrational dephasing due to the coupling with the solvent bath mode should be faster than the relaxation time of the bath mode for the excitation energy dependence of the Raman Stokes shift to be observed. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.477464
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  • 8
    Electronic Resource
    Electronic Resource
    Study of polar dumbbell fluids from the gaseous to the liquid densities by the reference interaction site model-1 and -2 integral equations (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 10084-10091 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The structures and the thermodynamic properties of a fluid composed of a nonpolar or a polar dumbbell molecule have been studied from the gaslike to the liquidlike density regions based on two types of the reference interaction site model (RISM) integral equation theories (RISM-1 and RISM-2). This is the first application of the RISM-2 theory to a polar dumbbell fluid. We have proven that the RISM-2 theory with the hypernetted-chain (HNC) approximation has an inconsistency with respect to the zeroth-order relation between site–site total correlation functions and site–site direct correlation functions in the Fourier space. An hypothetical bridge function is introduced to remedy this inconsistency, which works well to give good information on the structure and the dielectric constant in the lower-density region. On the other hand, the RISM-1 theory works well in the higher-density region, but not well in the lower-density region. Complemental application of these theories, that is, the RISM-1 theory for the high-density region and the RISM-2 theory for the low-density region, allows us to understand the properties of fluid over wide density regions. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472837
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  • 9
    Electronic Resource
    Electronic Resource
    Effect of Er:YAG laser treatment on the root canal walls of human teeth: an SEM study (1998)
    Oxford, UK : Blackwell Publishing Ltd
    Dental traumatology 14 (1998), S. 0 
    Details
    ISSN: 1600-0595
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract— The purposes of the study were to observe the morphological changes on root canal walls after instrumentation and irrigation, and assess the efficacy of conventional cleansing procedures and the effectiveness of Er:YAG laser in removing debris and smear layer from the root canal walls. Thirty-six endodontically treated human mandibular incisor teeth with single root canals were bisected longitudinally and divided into three groups of 12 teeth. Group 1 (Gl) was left unlased as a control. The teeth of group 2 (G2) and group 3 (G3) were irradiated by Er:YAG laser (laser parameters were set at 1 W, 100 mJ/pulse and 10 Hz) for 3 s and 5 s. The teeth were prepared for scanning electron microscope study. Control specimens showed debris and heavy smear layer obscuring the dentinal tubules at all levels in the canals. The root canal walls irradiated by Er:YAG laser were free of debris, with an evaporated smear layer and open dentinal tubules. These results suggested that Er:YAG laser irradiation had an efficient cleaning effect on the prepared root canal walls.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1600-9657.1998.tb00851.x
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  • 10
    Electronic Resource
    Electronic Resource
    Effect of argon laser irradiation on instrumented root canal wall (1998)
    Oxford, UK : Blackwell Publishing Ltd
    Dental traumatology 14 (1998), S. 0 
    Details
    ISSN: 1600-0595
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract— The objective of the study was to examine whether argon laser has a property to remove debris and smear layer from root canal walls. Twelve endodontically treated human maxillary molar teeth with three root canals were divided into two groups of six teeth. The first group was left unlased as a control; in the second group the root canals were irradiated by argon laser (laser parameters were set at 1 W and pulse duration and pulse frequency fixed at 0.05 s and 5 Hz). After the usual root canal preparation and lasing had been camed out, the teeth were decoronated, bisected longitudinally, observed with a scanning electron microscope and evaluated as to how clean the surfaces of root canal walls were. In most cases control teeth presented surfaces with debris covering the root canals, obscuring the dentinal tubules. Only 1 of 18 specimens was free of debris. In the lased group, root canal surfaces free of debris and vaporized pulpal tissue remnants were observed in 13 of 18 specimens. The results showed sigmficant statistical differences between the control group and the lased groups (P〈0.001). These results suggested that argon laser irradiation has an efficient cleaning effect on instrumented root canal surfaces.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1600-9657.1998.tb00805.x
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