Browsing by Author "Okajima, Hajime"

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Accurate intensity calibration for low wavenumber (-150 to 150cm(-1)) Raman spectroscopy using the pure rotational spectrum of N-2
(2015-11-01)
Okajima, Hajime
;
Hamaguchi, Hiro-o
;
應用化學系
;
應用化學系分子科學碩博班
;
Department of Applied Chemistry
We report on an accurate intensity calibration method for low wavenumber Raman spectroscopy. It uses the rotational Raman spectrum of N-2. The intensity distributions in the rotational Raman spectra of diatomic molecules are theoretically well established. They can be used as primary intensity standards for intensity calibration. The intensity ratios of the Stokes and anti-Stokes transitions originating from the same rotational levels are not affected by thermal population. Taking the effect of rotation-vibration interactions appropriately into account, we are able to calculate these intensity ratios theoretically. The comparison between the observed and calculated ratios of the N-2 pure rotational spectrum provides an accurate relative sensitivity curve (error similar to 5 x 10(-4)) in the wavenumber region of -150 to 150 cm(-1). We determine the temperature of water solely from the low wavenumber Raman spectra, using a thus calibrated spectrometer. The Raman temperature shows an excellent agreement with the thermocouple temperature, with only 0.5 K difference. The present calibration technique will be highly useful in many applications of low wavenumber quantitative Raman spectroscopy. Copyright (C) 2015 John Wiley & Sons, Ltd.
Automatic and objective oral cancer diagnosis by Raman spectroscopic detection of keratin with multivariate curve resolution analysis
(2016-01-25)
Chen, Po-Hsiung
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Shimada, Rintaro
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Yabumoto, Sohshi
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Okajima, Hajime
;
Ando, Masahiro
We have developed an automatic and objective method for detecting human oral squamous cell carcinoma (OSCC) tissues with Raman microspectroscopy. We measure 196 independent Raman spectra from 196 different points of one oral tissue sample and globally analyze these spectra using a Multivariate Curve Resolution (MCR) analysis. Discrimination of OSCC tissues is automatically and objectively made by spectral matching comparison of the MCR decomposed Raman spectra and the standard Raman spectrum of keratin, a well-established molecular marker of OSCC. We use a total of 24 tissue samples, 10 OSCC and 10 normal tissues from the same 10 patients, 3 OSCC and 1 normal tissues from different patients. Following the newly developed protocol presented here, we have been able to detect OSCC tissues with 77 to 92% sensitivity (depending on how to define positivity) and 100% specificity. The present approach lends itself to a reliable clinical diagnosis of OSCC substantiated by the "molecular fingerprint" of keratin.
Communication: Three-dimensional model for phonon confinement in small particles: Quantitative bandshape analysis of size-dependent Raman spectra of nanodiamonds
(2014-01-28)
Korepanov, Vitaly I.
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Witek, Henryk
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Okajima, Hajime
;
Osawa, Eiji
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Hamaguchi, Hiro-O
Raman spectroscopy of nano-scale materials is facing a challenge of developing a physically sound quantitative approach for the phonon confinement effect, which profoundly affects the phonon Raman band shapes of small particles. We have developed a new approach based on 3-dimensional phonon dispersion functions. It analyzes the Raman band shapes quantitatively in terms of the particle size distributions. To test the model, we have successfully obtained good fits of the observed phonon Raman spectra of diamond nanoparticles in the size range from 1 to 100 nm. (C) 2014 AIP Publishing LLC.
Formation of "Nano-Ice" and Density Maximum Anomaly of Water
(2018-06-01)
Okajima, Hajime
;
Ando, Masahiro
;
Hamaguchi, Hiro-o
;
應用化學系
;
應用化學系分子科學碩博班
Water is still mysterious despite intensive and extensive studies over the years. Anomalous behavior of water as a liquid is yet to be fully comprehended. Here we show that the most generally known anomaly of water, the density maximum anomaly, is well accounted for by the formation of nanometer-size ice crystallite at low temperatures. We show spectroscopically that, in cold and super-cooled water, this nanometer-size ice crystallite is formed and coexists with the other two forms of water. Multivariate hyperspectral analysis of 140 temperature dependent Raman spectra in the range of (_)23 similar to 45 degrees C determines the three distinct vibrational spectra of the three forms of water and their fractions at different temperatures. Simulation based on the determined fractions successfully reproduces the temperature dependence of density with a maximum at the right temperature. The mystery of the density maximum of water has thus been given an unequivocal solution. The nanometer-size ice crystallite might well be called "nano-ice".
Imaging molecular crystal polymorphs and their polycrystalline microstructures in situ by ultralow-frequency Raman spectroscopy
(2014-01-01)
Chang, Chun-Fu
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Okajima, Hajime
;
Hamaguchi, Hiro-o
;
Shigeto, Shinsuke
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應用化學系
Ultralow-frequency Raman spectroscopy that can measure vibrational bands at as low as +/- 10 cm(-1) has enabled facile in situ imaging of polycrystalline microstructures such as grains and grain boundaries with high polymorph specificity. We demonstrate this method by investigating microcrystals of two distinct polymorphs of 1,1\'-binaphthyl using a microscope.
Local structure formation in alkyl-imidazolium-based ionic liquids as revealed by linear and nonlinear Raman spectroscopy
(2007-11-01)
Iwata, Koichi
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Okajima, Hajime
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Saha, Satyen
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Hamaguchi, Hiro-O
;
應用化學系
We show several pieces of Raman spectroscopic evidence that are indicative of local structure formation in imidazolium-based ionic liquids. Low-frequency Raman spectra of C(n)mimX, where C(n)mim stands for 1-alkyl(CnH2n+1)-3-methylimidazolium cation and X represents the anion, exhibit broad bands assignable to collective modes of local structures. Spatial distributions of coherent anti-Stokes Raman scattering (CARS) signals from C(n)mim[PF(6)l are consistent with local structures whose size increases with increasing n. Picosecond Raman spectra of S, trans-stilbene as a "picosecond Raman thermometer" show microscopic thermal inhomogeneity ascribable to local structure formation in C(2)mimTf(2)N and C(4)mimTf(2)N. We also describe two novel phenomena that we believe are relevant to extraordinary nanoenvironments generated by local structures in a magnetic ionic liquid C(4)mim[FeCl4].
Microscopic solvation environments in a prototype room-temperature ionic liquid as elucidated by resonance Raman spectroscopy of iodine and bromine
(2017-04-05)
Saha, Satyen
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Okajima, Hajime
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Homma, Osamu
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Hamaguchi, Hiro-o
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應用化學系分子科學碩博班
Microscopic solvation environments in a prototype ionic liquid, bmimTf(2)N; 1-buty1-3-methyl-imidazoliumbis(trifluoromethanesulfonyl)imide, have been studied with the use of halides, X-2 and X-n(-) (X = I, Br; n = 3,5), as molecular probes. Resonance Raman spectroscopy has been used to detect these halogen species existing in bmimTf(2)N as well as in reference solvents including heptane, cyclohexane, KX/H2O and benzene. In heptane and cyclohexane, only free X-2 species are detected. In KX/H2O, only X-n(-) and, in benzene, only benzene-X-2 complexes are detected. On the contrary, free X-2 and X-n(-) are concomitantly detected in bmimTf(2)N, indicating that there are two distinct solvation environments in bmimTf(2)N, non-polar environments that solvate free X-2 and polar environments that stabilize X-n(-) These two distinct solvation environments are most likely to arise from microscopic structural heterogeneity of ionic liquids. (C) 2016 Elsevier B.V. All rights reserved.
Rotational dynamics of solvated carbon dioxide studied by infrared, Raman, and time-resolved infrared spectroscopies and a molecular dynamics simulation
(2012-01-07)
Watanabe, Kaori
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Okajima, Hajime
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Kato, Takuya
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Hamaguchi, Hiro-o
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應用化學系
Rotational dynamics of solvated carbon dioxide (CO(2)) has been studied. The infrared absorption band of the antisymmetric stretch mode in acetonitrile is found to show a non-Lorentzian band shape, suggesting a non-exponential decay of the vibrational and/or rotational correlation functions. A combined method of a molecular dynamics (MD) simulation and a quantum chemical calculation well reproduces the observed band shape. The analysis suggests that the band broadening is almost purely rotational, while the contribution from the vibrational dephasing is negligibly small. The non-exponential rotational correlation decay can be explained by a simple rotor model simulation, which can treat large angle rotations of a relatively small molecule. A polarized Raman study of the symmetric stretch mode in acetonitrile gives a rotational bandwidth consistent with that obtained from the infrared analysis. A sub-picosecond time-resolved infrared absorption anisotropy measurement of the antisymmetric stretch mode in ethanol also gives a decay rate that is consistent with the observed rotational bandwidths. (C) 2012 American Institute of Physics. [doi:10.1063/1.3671998]
Unusually Long trans/gauche Conformational Equilibration Time during the Melting Process of BmimC1, a Prototype Ionic Liquid
(2011-11-05)
Okajima, Hajime
;
Hamaguchi, Hiro-o
;
應用化學系
;
應用化學系分子科學碩博班
;
Department of Applied Chemistry
The melting process of 1-butyl-3-methylimidazolium chloride (bmimC1), a prototype room-temperature ionic liquid, has been studied with fast low frequency Raman spectroscopy. Simultaneous tracing of the lattice vibrations and trans/gauche conformational marker bands reveals that the conformational change in the butyl group occurs a few seconds after the loss of lattice vibrations. This finding indicates that the alkyl chain interaction in bmimC1 is so strong that the butyl conformation hardly changes in the very early stage of melting.