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Resonant secondary radiation spectra of dilute β-carotene solution (10−4–10−5 M) are measured under stationary excitation. The excitation energy is varied within 0–0 and 0–1 transition energies in the S2–S0 transition of β-carotene. When the excitation energy is varied from the peak of the 0–0 absorption band to the low-energy side at 60 K and 175...
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Context 1
... The temperature dependence of BR scattering is obtained in Sec. IV D. Assuming that the BR component mainly consists of first-order Raman scattering and spectral intensity is much narrower than the absorption spectrum in the temperature range from 200 K to 15 K, the shape of 0 () is determined by the BR scattering using Eqs. 7 and 18. As shown in Fig. 8, 0 () determined by dividing experimental data of BR scattering by 2 n T () 1 at each temperature are quite similar. We cannot ob- serve directly the line shape of 0 (;20 cm 1 because of the stray light by the excitation ...
Context 2
... shown in Fig. 8. Here c is a normalized coupling constant. We assume that the line shape of 0 () ( the peak en- ergy of WDOS is proportional to 2 , and that the peak energy is 20 cm 1 . This assumption is not so bad because the RSR spectra in intermediate or slow modulation systems is insensitive to line shape in low-energy region (20 cm 1 ...
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Citations
... The diode-pumped solid state laser light of our Raman microscope (532 nm) produces detectable photoluminescence emission (PL) in many hydrous basic copper compounds, such as carbonates, sulfates, phosphates, silicates and chlorides. Frequent publications focus on b-carotene Raman-PL spectroscopy in solution [23] but rarely on natural sediments with solid carotenoid. Solid carotenoids in copper ores collected in nature seem scarcely studied directly by luminescence techniques. ...
Subpicosecond time-resolved fluorescence spectra of all-trans-neurosporene and spheroidene, upon excitation above the 1Bu+ (v=2) and 1Bu+ (v=3) vibronic levels, respectively, were recorded by means of Kerr-gate spectroscopy. The spectral data matrices were analyzed by singular-value decomposition followed by global-fitting by the use of a sequential model. A pair of species-associated difference spectra thus obtained in each carotenoid was ascribed to fluorescence from the 1Bu+ (v=1) and 1Bu+ (v=0) vibronic levels down to the ground 1Ag- (v=0, 1 and 2) levels. The lifetimes of the 1Bu+ (v=1) and 1Bu+ (v=0) states were determined to be 50 and 260 fs in neurosporene and 25 and 260 fs in spheroidene.
The intra- and inter-molecular vibrational relaxation in the electronic excited state (1Bu+) of spheroidene derivative (the number of conjugated double bonds, n=8) has been investigated at room temperature by means of femtosecond time-resolved fluorescence spectroscopy based on an optical-Kerr-gate technique. Depending on the photo-excitation either to the 1Bu+(v=1) or 1Bu+(v=2) vibronic level, remarkable differences were observed in hot luminescence spectra related to the vibrational relaxation process of high- and low-frequency modes. Under the excitation to the 1Bu+(v=2) state hot luminescence from the 1Bu+(v=1) state was observed as a dominant feature of the time-resolved spectra while the dynamic Stokes shift originating from the low-frequency-modes dynamics was clearly observed under the excitation to the 1Bu+(v=1). These observations of the excitation energy dependence of time-resolved fluorescence spectra were discussed by analyzing the Franck–Condon factors of transitions from v=0,1, and 2 levels of high-frequency modes.
The metastable calcium carbonate polymorph vaterite has recently been found to occur commonly in freshwater cultured pearls from Japan and China. Organic pigment molecules in these vaterite regions of freshwater cultured pearls were analysed by resonance and near-resonance micro-Raman spectroscopy, in single spectra and in mapping modes and are compared with their aragonitic counterparts. Four different excitation wavelengths (487.9, 514.5, 532.2 and 632.8 nm) were used, resulting in differential increase of resolution for the pigments. Although vaterite areas were always lightly coloured (light yellow, light brown or white), ten different pigments were identified and a single colour is formed by a combination of three and up to nine polyenes of different lengths. The molecules were identified as unmethylated polyenes with effective chain lengths between 8 and 12 conjugated double bonds and FWHMs of 10 ± 2 cm−1. Additionally, and for the first time in pearls, methylated polyenes were detected together with unmethylated pigments in aragonite. Polyenes with chain lengths shorter than 8 or longer than 12 were not found in vaterite, whereas both shorter and longer pigment chains were observed in aragonite from the same pearls. Pigments have lower concentrations in vaterite and are distributed more homogeneously, while they have higher concentrations in aragonite and are arranged along the annual growth lines of the pearls. Copyright © 2008 John Wiley & Sons, Ltd.
In single-beam coherent anti-Stokes Raman scattering (CARS) spectroscopy, a complete CARS scheme is accomplished with tailored pulses from a fs-oscillator by coherent control of the nonlinear signal generation. Here, the application of single-beam CARS to low-wavenumber vibrational modes in the range of 50-400 cm(-1) is demonstrated by investigating pure liquid-phase samples and molecules in solution. The spectral resolution (17 cm(-1)) achieved by coherent control of the CARS process is an order of magnitude better than the spectral width of the excitation pulses (150 cm(-1) FWHM). At the same time, nonresonant background is suppressed by more than 1 order of magnitude. It is shown that spectral shaping of the excitation spectrum can drastically extend the accessible range of vibrational modes in single-beam CARS. The implemented scheme is very well suited for CARS microscopy because of its conceptual simplicity and flexibility, and presents the opportunity for spatially resolved studies of conformational modes in biological samples. Copyright (C) 2006 John Wiley & Sons, Ltd
Colonisation of wall paintings by microorganisms and other organisms is a well-known problematic phenomenon. Besides taxonomic identification of the biodeteriogen, it is essential to evaluate the consequences of the colonisation, e.g., unsightly coloured patinas. This work proposes new methodology for characterisation of the nature of the main carotenoids and their distribution in brown stains or patinas of a deteriorated wall painting on the north wall of the atrium of Marcus Lucretius House (Pompeii, Italy). Characterisation of the brown patinas and surrounding areas (plaster and polychromy) from the wall painting started with in situ screening using, mainly, a portable Raman instrument with a handheld FTIR (DRIFTS sampling interface) in order to select the sampling areas suitable for further analysis in the laboratory. Two wall painting fragments were then analysed in the laboratory in two steps. First, microscopic observations (SEM and phase-contrast microscopy) were used to determine whether biodeteriogens were present in the samples. In a second step, confocal Raman microscopy (785 and 514 nm excitation lasers) was used to characterise the main biogenic compounds of the brown stains. Because of the resonance Raman effect (514 nm excitation laser), it was possible to obtain reliable Raman features to assign not only the nature of the main biogenic pigments (carotenoids) present in the stains, but also their spatial conformation. Moreover, Raman confocal applications, for example, Raman imaging and depth profiling were also used in a first attempt to determine the distribution of biosynthesised carotenoids in the stains, and to determine the thickness of the brown patinas.
Carotenoids containing a carbonyl group in conjugation with their polyene backbone are naturally-occurring pigments in marine organisms and are essential to the photosynthetic light-harvesting function in aquatic algae. These carotenoids exhibit spectral characteristics attributed to an intramolecular charge transfer (ICT) state that arise in polar solvents due to the presence of the carbonyl group. Here, we report the spectroscopic properties of the carbonyl carotenoid fucoxanthin in polar (methanol) and nonpolar (cyclohexane) solvents studied by steady-state absorption and femtosecond pump-probe measurements. Transient absorption associated with the optically forbidden S(1) (2(1)A) state and/or the ICT state were observed following one-photon excitation to the optically allowed S(2) (1(1)B) state in methanol. The transient absorption measurements carried out in methanol showed that the ratio of the ICT-to-S(1) state formation increased with decreasing excitation energy. We also showed that the ICT character was clearly visible in the steady-state absorption in methanol based on a Franck-Condon analysis. The results suggest that two spectroscopic forms of fucoxanthin, blue and red, exist in the polar environment.
Raman spectra of acetylacetone were recorded for molecules isolated in an argon matrix at 10 K and for a polycrystalline sample. In the solid sample, broad bands appear superimposed on a much weaker Raman spectrum corresponding mainly to the stable enol form. The position of these bands depends on the excitation wavelength (514.5 and 488.8 nm argon ion laser lines were used), sample temperature, and cooling history. They are attributed to transitions from an excited electronic state to various isomer states in the ground electronic state. Laser photons have energies comparable to energies of a number of excited triplet states predicted for a free acetylacetone molecule (Chen, X.-B.; Fang, W.-H.; Phillips, D. L. J. Phys. Chem. A 2006, 110, 4434). Since singlet-to-triplet photon absorption transitions are forbidden, states existing in the solid have mixed singlet/triplet character. Their decay results in population of different isomer states, which except for the lowest isomers SYN enol, TS2 enol (described in Matanović I.; Doslić, N. J. Phys. Chem. A 2005, 109, 4185), and the keto form, which can be detected in the Raman spectra of the solid, are not vibrationally resolved. Differential scanning calorimetry detected two signals upon cooling of acetylacetone, one at 229 K and one at 217 K, while upon heating, they appear at 254 and 225 K. The phase change at higher temperature is attributed to a freezing/melting transition, while the one at lower temperature seems to correspond to freezing/melting of keto domains, as suggested by Johnson et al. (Johnson, M. R.; Jones, N. H.; Geis, A; Horsewill. A. J.; Trommsdorff, H. P. J. Chem. Phys. 2002, 116, 5694). Using matrix isolation in argon, the vibrational spectrum of acetylacetone at 10 K was recorded. Strong bands at 1602 and 1629 cm(-1) are assigned as the SYN enol bands, while a weaker underlying band at 1687 cm(-1) and a medium shoulder at 1617 cm(-1) are assigned as TS2 enol bands.
