VIBRATIONAL SPECTRUM OF THE THIOMETHOXY (CH$_3$S) RADICAL INVESTIGATED WITH INFRARED-VACUUM ULTRAVIOLET PHOTOIONIZATION
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Date
2011
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Ohio State University
Abstract
We produced methylthio (or thiomethoxy, CH$_3$S) radicals by photodissociation of CH$_3$SH in a supersonic jet at 248 nm. The CH$_3$S$^{+}$ ions were subsequently produced with the 1+1 IR-VUV photoionization and detected with the time-of-flight (TOF) technique. The IR spectrum of CH$_3$S was obtained on tuning the wavelength of the IR laser in the range 2780--3280 cm$^{-1}$ while monitoring the intensity of the CH$_3$S$^{+}$ signal; the frequency of the VUV laser was maintained at 134.8 nm, ~200 cm$^{-1}$ below the ionization threshold of CH$_3$S (IE = 9.225 eV). This technique has an advantage over other IR-absorption techniques because its mass selectivity eliminates interferences from the precursor and other photolysis products such as H$_2$CS, CH$_3$, or CH$_3$SS. Absorption bands near 2820, 2904, and 3215 cm$^{-1}$ were observed and tentatively assigned as transitions from the ground vibrational state to the 1$^{1}$, 4$^{1}$ (a$_1$), and 5$^{1}$6$^{2}$ states, respectively. These bands are in agreement with those reported for CH$_3$S produced via in situ photolysis of CH$_3$SH, CH$_3$SCH$_3$, and CH$_3$SSCH$_3$ isolated in solid p-H$_2$.$^{[1]}$ A new band near 2970 cm$^{-1}$ that is consistent with that observed in photoelectron spectrum$^{[2]}$ might be assigned to the transition from the ground vibrational state to the a$_1$ component of the 5$^{1}$6$^{2}$ state. . \bf{133}\rm, 164316 (2010).} \bf{108}\rm, 163 (2000).}
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Author Institution: Department of Applied Chemistry and Institute of Molecular Science, National Chiao Tung University, Hsinchu 30010, Taiwan.; Department of Applied Chemistry and Institute of Molecular Science, National Chiao Tung University, Hsinchu 30010, Taiwan and Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan.