Browsing by Author "Han, Hui-Ling"

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Infrared absorption of gaseous ClCS detected with time-resolved Fourier-transform spectroscopy
(2007-05-07)
Chu, Li-Kang
;
Han, Hui-Ling
;
Lee, Yuan-Pern
;
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.
Infrared absorption of methanethiol clusters (CH3SH)(n), n=2-5, recorded with a time-of-flight mass spectrometer using IR depletion and VUV ionization
(2012-12-21)
Fu, Lung
;
Han, Hui-Ling
;
Lee, Yuan-Pern
;
應用化學系
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應用化學系分子科學碩博班
We investigated IR spectra in the CH- and SH-stretching regions of size-selected methanethiol clusters, (CH3SH)(n) with n = 2-5, in a pulsed supersonic jet using infrared (IR)-vacuum ultraviolet (VUV) ionization. VUV emission at 132.50 nm served as the source of ionization in a time-of-flight mass spectrometer. Clusters were dissociated with light from a tunable IR laser before ionization. The variations in intensity of methanethiol cluster ions (CH3SH)(n)(+) were monitored as the IR laser light was tuned across the range 2470-3100 cm(-1). In the SH-stretching region, the spectrum of (CH3SH)(2) shows a weak band near 2601 cm(-1), red-shifted only 7 cm(-1) from that of the monomer. In contrast, all spectra of (CH3SH)(n), n = 3-5, show a broad band near 2567 cm(-1) with much greater intensity. In the CH-stretching region, absorption bands of (CH3SH)(2) are located near 2865, 2890, 2944, and 3010 cm(-1), red-shifted by 3-5 cm(-1) from those of CH3SH. These red shifts increase slightly for larger clusters and bands near 2856, 2884, 2938, and 3005 cm(-1) were observed for (CH3SH)(5). These spectral results indicate that the S-H center dot center dot center dot S hydrogen bond plays an important role in clusters with n = 3-5, but not in (CH3SH)(2), in agreement with theoretical predictions. The absence of a band near 2608 cm(-1) that corresponds to absorption of the non-hydrogen-bonded SH moiety and the large width of observed feature near 2567 cm(-1) indicate that the dominant stable structures of (CH3SH)(n), n = 3-5, have a cyclic hydrogen-bonded framework. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4770227]
Infrared absorption of methanol clusters (CH(3)OH)(n) with n=2-6 recorded with a time-of-flight mass spectrometer using infrared depletion and vacuum-ultraviolet ionization
(2011-04-14)
Han, Hui-Ling
;
Camacho, Cristopher
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Witek, Henryk A.
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Lee, Yuan-Pern
;
應用化學系
We investigated IR spectra in the CH-and OH-stretching regions of size-selected methanol clusters, (CH(3)OH)(n) with n = 2-6, in a pulsed supersonic jet by using the IR-VUV (vacuum-ultraviolet) ionization technique. VUV emission at 118 nm served as the source of ionization in a time-of-flight mass spectrometer. The tunable IR laser emission served as a source of predissociation or excitation before ionization. The variations of intensity of protonated methanol cluster ions (CH(3)OH)(n)H(+) and CH(3)OH(+) and (CH(3)OH)(2)(+) were monitored as the IR laser light was tuned across the range 2650-3750 cm(-1). Careful processing of these action spectra based on photoionization efficiencies and the production and loss of each cluster due to photodissociation yielded IR spectra of the size-selected clusters. Spectra of methanol clusters in the OH region have been extensively investigated; our results are consistent with previous reports, except that the band near 3675 cm(-1) is identified as being associated with the proton acceptor of (CH(3)OH)(2). Spectra in the CH region are new. In the region 2800-3050 cm(-1), bands near 2845, 2956, and 3007 cm(-1) for CH(3)OH split into 2823, 2849, 2934, 2955, 2984, and 3006 cm(-1) for (CH(3)OH)(2) that correspond to proton donor and proton acceptor, indicating that the methanol dimer has a preferred open-chain structure. In contrast, for (CH(3)OH)(3), the splitting diminishes and the bands near 2837, 2954, and 2987 cm(-1) become narrower, indicating a preferred cyclic structure. Anharmonic vibrational wavenumbers predicted for the methanol open-chain dimer and the cyclic trimer with the B3LYP/VPT2/ANO1 level of theory are consistent with experimental results. For the tetramer and pentamer, the spectral pattern similar to that of the trimer but with greater widths was observed, indicating that the most stable structures are also cyclic. (C) 2011 American Institute of Physics. [doi:10.1063/1.3572225]
Infrared absorption of methanol clusters (CH3OH)(n) with n=2-6 recorded with a time-of-flight mass spectrometer using infrared depletion and vacuum-ultraviolet ionization
(2011-04-14)
Han, Hui-Ling
;
Camacho, Cristopher
;
Witek, Henryk A.
;
Lee, Yuan-Pern
;
應用化學系
We investigated IR spectra in the CH-and OH-stretching regions of size-selected methanol clusters, (CH3OH)(n) with n = 2-6, in a pulsed supersonic jet by using the IR-VUV (vacuum-ultraviolet) ionization technique. VUV emission at 118 nm served as the source of ionization in a time-of-flight mass spectrometer. The tunable IR laser emission served as a source of predissociation or excitation before ionization. The variations of intensity of protonated methanol cluster ions (CH3OH)(n)H+ and CH3OH+ and (CH3OH)(2)(+) were monitored as the IR laser light was tuned across the range 2650-3750 cm(-1). Careful processing of these action spectra based on photoionization efficiencies and the production and loss of each cluster due to photodissociation yielded IR spectra of the size-selected clusters. Spectra of methanol clusters in the OH region have been extensively investigated; our results are consistent with previous reports, except that the band near 3675 cm(-1) is identified as being associated with the proton acceptor of (CH3OH)(2). Spectra in the CH region are new. In the region 2800-3050 cm(-1), bands near 2845, 2956, and 3007 cm(-1) for CH3OH split into 2823, 2849, 2934, 2955, 2984, and 3006 cm(-1) for (CH3OH)(2) that correspond to proton donor and proton acceptor, indicating that the methanol dimer has a preferred open-chain structure. In contrast, for (CH3OH)(3), the splitting diminishes and the bands near 2837, 2954, and 2987 cm(-1) become narrower, indicating a preferred cyclic structure. Anharmonic vibrational wavenumbers predicted for the methanol open-chain dimer and the cyclic trimer with the B3LYP/VPT2/ANO1 level of theory are consistent with experimental results. For the tetramer and pentamer, the spectral pattern similar to that of the trimer but with greater widths was observed, indicating that the most stable structures are also cyclic. (C) 2011 American Institute of Physics. [doi:10.1063/1.3572225]
Infrared spectrum of mass-selected CH(3)S radicals investigated with infrared plus vacuum ultraviolet photoionization
(2011-10-17)
Han, Hui-Ling
;
Fu, Lung
;
Lee, Yuan-Pern
;
應用化學系
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應用化學系分子科學碩博班
We present a detailed spectral study of the atmospherically important methylthio (CH(3)S) radical demonstrating the advantage of IR-VUV photoionization for vibrational spectroscopy of free radicals due to its mass selectivity. Photolysis of CH(3)SH produced CH(3)S radicals that were ionized with (1 + 1) IR-VUV photoionization and detected with the time-of-flight technique. The IR spectrum of CH(3)S was obtained in the range 2790-3270 cm (1). Absorptions features near 2819 and 2904 cm (1) are assigned to nu(1) and nu(4) modes of CH(3)S, respectively, and those near 2978 and 3241 cm (1) are tentatively assigned as combination transitions 3(1)5(1)6(1)(e) and 3(1)5(1)6(1)(a), respectively, from the ground vibrational state. (C) 2011 Elsevier B.V. All rights reserved.
Infrared spectrum of mass-selected CH3S radicals investigated with infrared plus vacuum ultraviolet photoionization
(2011-10-17)
Han, Hui-Ling
;
Fu, Lung
;
Lee, Yuan-Pern
;
應用化學系
;
應用化學系分子科學碩博班
We present a detailed spectral study of the atmospherically important methylthio (CH3S) radical demonstrating the advantage of IR-VUV photoionization for vibrational spectroscopy of free radicals due to its mass selectivity. Photolysis of CH3SH produced CH3S radicals that were ionized with (1 + 1) IR-VUV photoionization and detected with the time-of-flight technique. The IR spectrum of CH3S was obtained in the range 2790-3270 cm (1). Absorptions features near 2819 and 2904 cm (1) are assigned to nu(1) and nu(4) modes of CH3S, respectively, and those near 2978 and 3241 cm (1) are tentatively assigned as combination transitions 3(1)5(1)6(1)(e) and 3(1)5(1)6(1)(a), respectively, from the ground vibrational state. (C) 2011 Elsevier B.V. All rights reserved.