Browsing by Author "Fu, Lung"

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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
;
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 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
;
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.