Browsing by Author "Chu, Li-Kang"

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Infrared absorption of C6H5SO2 detected with time-resolved Fourier-transform spectroscopy
(2007-04-07)
Chu, Li-Kang
;
Lee, Yuan-Pern
;
應用化學系
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應用化學系分子科學碩博班
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Department of Applied Chemistry
C6H5SO2 radicals were produced upon irradiation of three flowing mixtures: C6H5SO2Cl in N-2, C6H5Cl and SO2 in CO2, and C6H5Br and SO2 in CO2, with a KrF excimer laser at 248 nm. A step-scan Fourier-transform spectrometer coupled with a multipass absorption cell was employed to record the time-resolved infrared (IR) absorption spectra of reaction intermediates. Two transient bands with origins at 1087.7 and 1278.2 cm(-1) are assigned to the SO2-symmetric and SO2-antisymmetric stretching modes, respectively, of C6H5SO2. Calculations with density-functional theory (B3LYP/aug-cc-pVTZ and B3P86/aug-cc-pVTZ) predict the geometry and vibrational wave numbers of C6H5SO2 and C6H5OSO. The vibrational wave numbers and IR intensities of C6H5SO2 agree satisfactorily with the observed new features. Rotational contours of IR spectra of C6H5SO2 simulated based on predicted molecular parameters agree satisfactorily with experimental results for both bands. The SO2-symmetric stretching band is dominated by a- and c-type rotational structures and the SO2-antisymmetric stretching band is dominated by a b-type rotational structure. When C6H5SO2Cl was used as a precursor of C6H5SO2, C6H5SO2Cl was slowly reproduced at the expense of C6H5SO2, indicating that the reaction Cl+C6H5SO2 takes place. When C6H5Br/SO2/CO2 was used as a precursor of C6H5SO2, features at 1186 and 1396 cm(-1) ascribable to C6H5SO2Br were observed at a later period due to secondary reaction of C6H5SO2 with Br. Corresponding kinetics based on temporal profiles of observed IR absorption are discussed. (c) 2007 American Institute of Physics.
Infrared absorption of gaseous c-ClCOOH and t-ClCOOH recorded with a step-scan Fourier-transform spectrometer
(2009-05-07)
Chu, Li-Kang
;
Lee, Yuan-Pern
;
應用化學系
;
應用化學系分子科學碩博班
;
Department of Applied Chemistry
Two conformers of ClCOOH were produced upon irradiation at 355 nm of a gaseous flowing mixture of Cl(2), HCOOH, and N(2). A step-scan Fourier-transform infrared spectrometer coupled with a multipass absorption cell was utilized to monitor the transient spectra of ClCOOH. Absorption bands with origins at 1808.0 and 1328.5 cm(-1) are attributed to the C=O stretching and COH bending modes of t-ClCOOH, respectively; those at 1883.0 and 1284.9 cm(-1) are assigned as the C=O stretching and COH bending modes of c-ClCOOH, respectively. These observed vibrational wavenumbers agree with corresponding values for t-ClCOOH and c-ClCOOH predicted with B3LYP/aug-cc-pVTZ density-functional theory and the observed rotational contours agree satisfactorily with simulated bands based on predicted rotational parameters. The observed relative intensities indicate that t-ClCOOH is more stable than c-ClCOOH by similar to 3 kJ mol(-1). A simple kinetic model is employed to account for the production and decay of ClCOOH.
Infrared absorption of gaseous CH(3)OO detected with a step-scan Fourier-transform spectrometer
(2007-12-21)
Huang, Deng-Ruei
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Chu, Li-Kang
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Lee, Yuan-Pern
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應用化學系分子科學碩博班
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Institute of Molecular science
CH(3)OO radicals were produced upon irradiation of a flowing mixture of CH(3)I and O(2) with a KrF excimer laser at 248 nm. A step-scan Fourier-transform spectrometer coupled with a multipass absorption cell was employed to record temporally resolved IR absorption spectra of reaction intermediates. Transient absorption bands with origins at 3033, 2954, 1453, 1408, 1183, 1117, 3020, and 1441 cm(-1) are assigned to nu(1)-nu(6), nu(9), and nu(10) modes of CH(3)OO, respectively, close to wavenumbers reported for CH(3)OO isolated in solid Ar. Calculations with density-functional theory (B3LYP/aug-cc-pVTZ) predicted the geometry and the vibrational wavenumbers of CH(3)OO; the vibrational wavenumbers and relative IR intensities of CH(3)OO agree satisfactorily with these observed features. The rotational contours of IR spectra of CH(3)OO, simulated based on ratios of predicted rotational parameters for the upper and lower states and on experimental rotational parameters of the ground state, agree satisfactorily with experimental results; the mixing ratios of a-, b-, and c-types of rotational structures were evaluated based on the direction of dipole derivatives predicted quantum chemically. A feature at 995 cm(-1), ascribed to CH(3)OOI from a secondary reaction of CH(3)OO with I, was also observed. (c) 2007 American Institute of Physics.
Infrared absorption of gaseous CH3OO detected with a step-scan Fourier-transform spectrometer
(2007-12-21)
Huang, Deng-Ruei
;
Chu, Li-Kang
;
Lee, Yuan-Pern
;
應用化學系
;
應用化學系分子科學碩博班
CH3OO radicals were produced upon irradiation of a flowing mixture of CH3I and O-2 with a KrF excimer laser at 248 nm. A step-scan Fourier-transform spectrometer coupled with a multipass absorption cell was employed to record temporally resolved IR absorption spectra of reaction intermediates. Transient absorption bands with origins at 3033, 2954, 1453, 1408, 1183, 1117, 3020, and 1441 cm(-1) are assigned to nu(1)-nu(6), nu(9), and nu(10) modes of CH3OO, respectively, close to wavenumbers reported for CH3OO isolated in solid Ar. Calculations with density-functional theory (B3LYP/aug-cc-pVTZ) predicted the geometry and the vibrational wavenumbers of CH3OO; the vibrational wavenumbers and relative IR intensities of CH3OO agree satisfactorily with these observed features. The rotational contours of IR spectra of CH3OO, simulated based on ratios of predicted rotational parameters for the upper and lower states and on experimental rotational parameters of the ground state, agree satisfactorily with experimental results; the mixing ratios of a-, b-, and c-types of rotational structures were evaluated based on the direction of dipole derivatives predicted quantum chemically. A feature at 995 cm(-1), ascribed to CH3OOI from a secondary reaction of CH3OO with I, was also observed. (c) 2007 American Institute of Physics.
Infrared absorption of gaseous ClCS detected with time-resolved Fourier-transform spectroscopy
(2007-05-07)
Chu, Li-Kang
;
Han, Hui-Ling
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Lee, Yuan-Pern
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應用化學系
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應用化學系分子科學碩博班
A transient infrared absorption spectrum of gaseous ClCS was detected with a step-scan Fourier-transform spectrometer coupled with a multipass absorption cell. ClCS was produced upon irradiating a flowing mixture of Cl2CS and N-2 or CO2 with a KrF excimer laser at 248 nm. A transient band in the region of 1160-1220 cm(-1), which diminished on prolonged reaction, is assigned to the C-S stretching (nu(1)) mode of ClCS. Calculations with density-functional theory (B3P86 and B3LYP/aug-cc-pVTZ) predict the geometry, vibrational wave numbers, and rotational parameters of ClCS. The rotational contour of the spectrum of ClCS simulated based on predicted rotational parameters agrees satisfactorily with experimental observation; from spectral simulation, the band origin is determined to be at 1194.4 cm(-1). Reaction kinetics involving ClCS, CS, and CS2 are discussed. (C) 2007 American Institute of Physics.
Study of the reactive excited-state dynamics of delipidated bacteriorhodopsin upon surfactant treatments
(2012-06-29)
Cheng, Chi-Wen
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Lee, Yuan-Pern
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Chu, Li-Kang
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應用化學系
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應用化學系分子科學碩博班
The dynamics of the reactive excited-state of bacteriorhodopsin treated with various surfactants have been investigated through the measurement of pump-probe absorption spectra. Upon excitation of bR at 570 nm in the presence of ionic surfactants CTAB and SDS, the lifetime of the reactive excited-state of the all-trans protonated Schiff base, probed at 460 nm, was observed to increase up to 20%, whereas an insignificant change was observed upon addition of neutral surfactant C6E2. Measurements of steady-state absorption spectra, fluorescence, and circular dichroism indicated that the bR suspensions retain their trimeric configuration with partial delipidation. This removal of lipids causes a structural alteration and the varied excited-state dynamics. (C) 2012 Elsevier B. V. All rights reserved.
The v(7), v(8), and v(11) bands of propynal, C(2)HCHO, in the 650 cm(-1) region
(2008-12-01)
McKellar, A. R. W.
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Watson, J. K. G.
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Chu, Li-Kang
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Lee, Yuan-Pern
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應用化學系
The infrared spectrum of propynal, C(2)HCHC, is studied at high resolution (0.003 cm(-1)) in the range 570640 cm(-1). The relatively intense v(11) (C equivalent to C-H out-of-plane bend, 693 cm(-1)) and v(7) (C equivalent to C-H in-plane bend, 651 cm(-1)) fundamental bands are linked by a strong a-type Coriolis interaction. The somewhat weaker v(8) (CCO in-plane bend, 614 cm(-1)) fundamental has a significant Fermi-type interaction with the "dark" background state 3v(9) (similar to 618 cm(-1)). About 1400 lines are assigned and analyzed in terms of a four-state fit in order to obtain accurate band origins, rotational and centrifugal distortion parameters, and Fermi and Coriolis interaction parameters. This represents the first systematic high-resolution infrared study of propynal. Crown Copyright (C) 2008 Published by Elsevier Inc. All rights reserved.
Transient Infrared Absorption Spectra of Reaction Intermediates Detected with a Step-scan Fourier-transform Infrared Spectrometer
(2014-01-01)
Huang, Yu-Hsuan
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Chen, Jin-Dah
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Hsu, Kuo-Hsiang
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Chu, Li-Kang
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Lee, Yuan-Pern
Our group has utilized a step-scan FTIR spectrometer operating in the absorption mode to characterize transient species in chemical reactions upon photo-irradiation of gaseous mixtures in a multipass White cell. The operational temporal resolution is typically 1-10 s with spectral resolution 0.1-4 cm(-1), depending on conditions. The acquisition of both ac- and dc-coupled signals enables an extraction of minute changes in the large background signal to attain a typical detectable absorbance variation greater than 1 x 10(-4). By consideration of reaction mechanisms and comparison of vibrational wavenumbers, IR intensities, and rotational contours predicted with theoretical calculations, we have assigned IR absorption bands of many important atmospheric free radicals and unstable species including their conformers, such as ClCO, ClSO, ClCS, ClCOOH, CH3SO2, CH3SOO, CH3OSO, CH3SO, CH3OO, CH3C(O)OO, CH2OO C6H5CO, C6H5SO2, and C6H5C(O)OO. The advantages and limitations of this technique to perform spectral and kinetic investigations of transient species in chemical reactions are discussed.
Transient infrared spectra of CH(3)SOO and CH(3)SO observed with a step-scan Fourier-transform spectrometer
(2010-11-14)
Chu, Li-Kang
;
Lee, Yuan-Pern
;
應用化學系
;
應用化學系分子科學碩博班
;
Department of Applied Chemistry
A step-scan Fourier-transform spectrometer coupled with a multipass absorption cell was employed to monitor time-resolved infrared absorption of transient species produced upon irradiation at 248 nm of a flowing mixture of CH(3)SSCH(3) and O(2) at 260 K. Two transient bands observed with origins at 1397 +/- 1 and 1110 +/- 3 cm(-1) are tentatively assigned to the antisymmetric CH(3)-deformation and O-O stretching modes of syn-CH(3)SOO, respectively; the observed band contour indicates that the less stable anti-CH(3)SOO conformer likely contributes to these absorption bands. A band with an origin at 1071 +/- 1 cm(-1), observed at a slightly later period, is assigned to the S=O stretching mode of CH(3)SO, likely produced via secondary reactions of CH(3)SOO. These bands fit satisfactorily with vibrational wavenumbers and rotational contours simulated based on rotational parameters of syn-CH(3)SOO, anti-CH(3)SOO, and CH(3)SO predicted with density-functional theories B3LYP/aug-cc-pVTZ and B3P86/aug-cc-pVTZ. Two additional bands near 1170 and 1120 cm(-1) observed at a later period are tentatively assigned to CH(3)S(O)OSCH(3) and CH(3)S(O)S(O)CH(3), respectively; both species are likely produced from self-reaction of CH(3)SOO. The production of SO(2) via secondary reactions was also observed and possible reaction mechanism is discussed. (C) 2010 American Institute of Physics. [doi:10.1063/1.3495765]
Transient infrared spectra of CH3SOO and CH3SO observed with a step-scan Fourier-transform spectrometer
(2010-11-14)
Chu, Li-Kang
;
Lee, Yuan-Pern
;
應用化學系
;
應用化學系分子科學碩博班
;
Department of Applied Chemistry
A step-scan Fourier-transform spectrometer coupled with a multipass absorption cell was employed to monitor time-resolved infrared absorption of transient species produced upon irradiation at 248 nm of a flowing mixture of CH3SSCH3 and O-2 at 260 K. Two transient bands observed with origins at 1397 +/- 1 and 1110 +/- 3 cm(-1) are tentatively assigned to the antisymmetric CH3-deformation and O-O stretching modes of syn-CH3SOO, respectively; the observed band contour indicates that the less stable anti-CH3SOO conformer likely contributes to these absorption bands. A band with an origin at 1071 +/- 1 cm(-1), observed at a slightly later period, is assigned to the S=O stretching mode of CH3SO, likely produced via secondary reactions of CH3SOO. These bands fit satisfactorily with vibrational wavenumbers and rotational contours simulated based on rotational parameters of syn-CH3SOO, anti-CH3SOO, and CH3SO predicted with density-functional theories B3LYP/aug-cc-pVTZ and B3P86/aug-cc-pVTZ. Two additional bands near 1170 and 1120 cm(-1) observed at a later period are tentatively assigned to CH3S(O)OSCH3 and CH3S(O)S(O)CH3, respectively; both species are likely produced from self-reaction of CH3SOO. The production of SO2 via secondary reactions was also observed and possible reaction mechanism is discussed. (C) 2010 American Institute of Physics. [doi:10.1063/1.3495765]