Browsing by Author "Lu, Hsiao-Chi"

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Absorption cross sections of NH3, NH2D, NHD2, and ND3 in the spectral range 140-220 nm and implications for planetary isotopic fractionation
(2006-08-20)
Cheng, Bing-Ming
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Lu, Hsiao-Chi
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Chen, Hong-Kai
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Bahou, Mohammed
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Lee, Yuan-Pern
Cross sections for photoabsorption of NH3, NH2D, NHD2, and ND3 in the spectral region 140-220 nm were determined at similar to 298 K using synchrotron radiation. Absorption spectra of NH2D and NHD2 were deduced from spectra of mixtures of NH3 and ND3, of which the equilibrium concentrations for all four isotopologues obey statistical distributions. Cross sections of NH2D, NHD2, and ND3 are new. Oscillator strengths, an integration of absorption cross sections over the spectral lines, for both A X and B X systems of NH3 agree satisfactorily with previous reports; values for NH2D, NHD2, and ND3 agree with quantum chemical predictions. The photolysis of NH3 provides a major source of reactive hydrogen in the lower stratosphere and upper troposphere of giant planets such as Jupiter. Incorporating the measured photoabsorption cross sections of NH3 and NH2D into the Caltech/JPL photochemical diffusive model for the atmosphere of Jupiter, we find that the photolysis efficiency of NH2D is lower than that of NH3 by as much as 30%. The D/H ratio in NH2D/NH3 for tracing the microphysics in the troposphere of Jupiter is also discussed.
Absorption spectra in the vacuum ultraviolet region of methanol in condensed phases
(2007-10-15)
Kuo, Yu-Ping
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Lu, Hsiao-Chi
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Wu, Yu-Jong
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Cheng, Bing-Ming
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Ogilvie, J. F.
With radiation from a synchrotron we measured the spectra of pure solid methanol and of methanol dispersed in solid argon (molar ratio 200) and krypton (molar ratio 250) at 10 K from the onset of absorption in the vacuum ultraviolet region until the limits imposed by LiF windows or the Ar or Kr dispersant. We fitted the total absorption profile divided by wavenumber to gaussian curves of minimal number. and made tentative assignments of electronic transitions and vibrational structure by comparison with spectra of gaseous methanol and with energies and intensities from our published quantum-chemical calculations. (C) 2007 Elsevier B.V. All rights reserved.
Absorption spectra in the vacuum ultraviolet region of small molecules in condensed phases
(2008-12-15)
Lu, Hsiao-Chi
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Chen, Hong-Kai
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Cheng, Bing-Ming
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Ogilvie, J. F.
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材料科學與工程學系
With radiation from a synchrotron we measured the spectra of several small molecular species in the, solid phase at 10K, either pure -O(2), NO, CO(2), N(2)O, H(2)O and NH(3) - or, for NH3 also dispersed in Ar at, molar ratio 1/250, from the onset of absorption in the ultraviolet region until the limits of transmission by crystalline LiF or solid At. In a quantitative treatment of spectral data, we fitted the total absorption profile divided by wavenumber to Gaussian curves of minimal number, and made tentative assignments of electronic transitions and vibrational structure by comparison with spectra of gaseous species. These results illuminate the nature of electronic spectra of samples in solid phases in the vacuum ultraviolet region. (C) 2008 Elsevier B.V. All rights reserved.
BaMgAl10O17 : Eu blue phosphors with MgO coating and microwave irradiation
(2008-02-01)
Kuo, Kuan-Ting
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Lee, Shu-Ping
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Chen, San-Yuan
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Cheng, Bing-Ming
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Lu, Hsiao-Chi
Europium-activated barium magnesium aluminate (BaMgAl10O17:Eu (BAM)) phosphor particles were modified by surface coating with MgO using a polyol method. The photoluminescence (PL) properties of the MgO-coated BAM phosphors showed slightly improved blue-emission intensity compared to the unmodified ones, and reached a stronger peak intensity with 5.25% MgO coating, under vacuum ultraviolet (VUV) 147 nm excitation. Upon microwave irradiation on the MgO-coated BAM phosphors, the PL properties of the MgO-coated phosphors exhibited a much enhanced relative PL ratio, and a maximum relative PL ratio can be achieved when as high as 10.5% MgO was deposited on the phosphor surface. However, for mechanically ground phosphor powder, it was found that although the intensity of the MgO-coated BAM turned stronger with increasing MgO concentration under microwave irradiation, the purity of the resulting luminescence was slightly disrupted by the presence of a new peak near 470 nm, corresponding to BaMg3Al14O25 compound. (C) 2007 Elsevier Ltd. All rights reserved.
Effect of alkyl position of pyrrole on structures and properties of conjugated polysquaraines
(2010-05-01)
Lu, Hsiao-Chi
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Whang, Wha-Tzong
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Cheng, Bing-Ming
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材料科學與工程學系
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Department of Materials Science and Engineering
Poly(1-octylpyrrolyl)squaraine and poly(3-octylpyrrolyl)squaraine were synthesized from squaric acid with 1-octylpyrrole and 3-octylpyrrole under identical conditions of condensation. Visible absorption spectra, photoluminescence spectra, TGA curves, and IR spectra were recorded to characterize the structures of these polymers as synthesized: the measured optical and thermal properties are consistent with backbone structures. The polysquaraine from 3-octylpyrrole possesses mostly zwitterionic repeating units (>97%), but the polymer from 1-octylpyrrole consists of zwitterionic and covalent repeating units in a ratio 2:1. Observations from the visible absorption and photoluminescence spectra in varied solvents, TGA curves, and thermal IR measurements for these two polymers reconciled to their structures. This result indicates that the position of the alkyl group in the pyrrole derivative affects the conformation in the condensation of poly(pyrrolyl)squaraine. These polysquaraines are stable below temperature 155 C and their visible absorption and photoluminescence properties in hydrogen-bonding solvents exhibit negative solvatochromism. (C) 2010 Elsevier B.V. All rights reserved.
Effect of microwave irradiation on surface characteristics and luminescent properties of BaMgAl10O17 : Eu blue phosphor
(2008-02-01)
Kuo, Kuan-Ting
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Lee, Shu-Ping
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Chen, San-Yuan
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Cheng, Bing-Ming
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Lu, Hsiao-Chi
BaMgAl10O17:Eu (BAM) has been an excellent blue-emitting phosphor due to its outstanding luminescence efficiency and purity for plasma display panels. An attempt of employing microwave irradiation to modify the surface properties including morphology and crystallinity of BAM powder was performed in this work. X-ray powder diffraction (XRD) analysis and scanning electron microscopy (SEM) images show that the blue-emitting phosphors after microwave irradiation treatment exhibit better crystallinity and smoother surface. Furthermore, the vacuum ultraviolet photoluminescence spectra show that the luminescent intensity of BAM phosphors can be effectively enhanced by a factor of six times under microwave irradiation treatment. The enhanced luminescent properties can be closely related to the surface modification and reduced defects of the BAM blue-emitting phosphors. (C) 2007 Elsevier Ltd. All rights reserved.
Humidity-switch chromism of aniline-pentamer in Nafion
(2016-08-19)
Lin, Yen-Hao
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Hsiao, Yu-Sheng
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Lu, Hsiao-Chi
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Chen, Peilin
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Whang, Wha-Tzong
Aniline-pentamer (AP) in Nafion triggered with humidity content displays an interesting chromism from blue to pink, which is much wider of color shift than general polyaniline. Thermogravimetric analysis confirms the reversal color change related to the moisture content in the sample. IR absorption spectra make known AP having high degree of protonation at lower water content. UV-Vis absorption expose the chromism process having something more than just protonation. The change of electronic energy levels and PL spectra reveal that there must be a complex interaction in NaAP. Raman scattering mapping confirms that drying causes the - SO3- hydrophilic channels transforming to isolated domains dispersed in matrix, which induces heavy protonation and complexation of AP with - SO3- groups. We can infer that the interesting humidity-switch chromism is due to the reversible protonation/deprotonation as well as complexation of AP with - SO3- groups through the reversible change of Nafion\'s morphology.
Isotopic fractionation of nitrogen in ammonia in the troposphere of Jupiter
(2007-03-10)
Liang, Mao-Chang
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Cheng, Bing-Ming
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Lu, Hsiao-Chi
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Chen, Hong-Kai
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Alam, M. S.
Laboratory measurements of the photoabsorption cross section of (NH3)-N-15 at wavelengths between 140 and 220 nm are presented for the first time. Incorporating the measured photoabsorption cross sections of (NH3)-N-15 and (NH3)-N-14 into a one-dimensional photochemical diffusive model, we find that at 400 mbar, the photolytic efficiency of (NH3)-N-15 is about 38% greater than that of (NH3)-N-14. In addition, it is known that ammonia can condense in the region between 200 and 700 mbar, and the condensation tends to deplete the abundance ratio of (NH3)-N-15 and (NH3)-N-14. By matching the observed ratio of (NH3)-N-15 and (NH3)-N-14 at 400 mbar, the combined effect of photolysis and microphysics produces the ratio of (2.42 +/- 0.34) x 10(-3) in the deep atmosphere, in excellent agreement with the Galileo spacecraft measurements. The usefulness of the isotopic composition of ammonia as a tracer of chemical and dynamical processes in the troposphere of Jupiter is discussed.
Photoabsorption cross sections of NH3, NH2D, NHD2, and ND3 in the spectral range 110-144 nm
(2007-10-21)
Wu, Yu-Jong
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Lu, Hsiao-Chi
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Chen, Hong-Kai
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Cheng, Bing-Ming
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Lee, Yuan-Pern
Cross sections for photoabsorption of NH3, NH2D, NHD2, and ND3 near 298 K were measured in the spectral range of 110-144 nm using radiation from a synchrotron. Absorption cross sections and oscillator strengths of NH3 agree satisfactorily with previous reports; those of ND3 are improved over those in a previous report, whereas those of NH2D and NHD2 are new. The oscillator strengths of transitions to D, D-', D-'', F, and G states are nearly the same among all four isotopic variants, but those to D-''' and E states vary substantially. Observed absorption bands are arranged into vibrational progressions in accord with known Rydberg transitions. All progressions show a common trend of vibrational intervals increasing with vibrational quantum numbers. The Rydberg orbitals for states D(3de('')), D-'(4sa(1)(')), D-''(3da(1)(')), D-'''(4pe(')), and E(4de('')) are readily assigned with quantum defects determined in these experiments, but assignments for F(5de('')) and G(6de('')) are uncertain. Absorption cross sections of dissociative continua underneath discrete structures are larger for NH2D and NHD2 than for NH3 and ND3, indicating that the rate of dissociation of ammonia might increase when its symmetry is broken. (C) 2007 American Institute of Physics.
Reversible isomerization of a zwitterionic polysquaraine induced by a metal surface
(2011)
Lu, Hsiao-Chi
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Whang, Wha-Tzong
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Cheng, Bing-Ming
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材料科學與工程學系
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Department of Materials Science and Engineering
The variation of visible and IR absorption spectra and of small-angle X-ray scattering of poly(3-octylpyrrole)squaraine in trichloromethane solution indicates that, for this zwitterionic conducting polymer (CP), a reversible change of conformation is induced by contact of the solution with the surface of an active metal. The structure of the target polymer might switch from being linear to being folded. For a copper surface, the activation energy of isomerization between the two forms, whatever their nature, is 18.9 +/- 0.7 kJ mol(-1), whereas for the reverse process the activation energy is 38 +/- 6 kJ mol(-1). In a folding transformation, formation of intramolecular hydrogen bonds might play a key role. This observation of a reversible conformation for a zwitterionic polymer induced by a metallic surface provides an impetus to investigate both such a structural modification of other CP and applications of this phenomenon.
Switchable structural modification accompanying altered optical properties of a zwitterionic polysquaraine
(2010-11-01)
Lu, Hsiao-Chi
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Whang, Wha-Tzong
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Cheng, Bing-Ming
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材料科學與工程學系
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Department of Materials Science and Engineering
Active metals induce a variation of the conformation of zwitterionic conducting polymer poly(3-octylpyrrole)squaraine in solution. Evidence from infrared, visible and photoluminescent spectra and from small-angle X-ray scattering profiles unambiguously confirms the isomerization of this polysquaraine induced by the surfaces of active metals. Unlike the irreversible change induced by cations in solution, the folded conformation induced by active metals reverts to its original structure on eliminating contact between the metals and the solution. Accompanied by altered optical properties, this reversible structural modification of the zwitterionic polysquaraine induced by active metals represents a new chemical and physical process. (C) 2010 Elsevier B.V. All rights reserved.