Browsing by Author "Xie, Tingxian"

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Barrierless reactions between two closed-shell molecules. I. Dynamics of F(2)+CH(3)SCH(3) reaction
(2008-03-14)
Lu, Yu-Ju
;
Lee, Lance
;
Pan, Jun-Wei
;
Xie, Tingxian
;
Witek, Henryk A.
A detailed experimental and theoretical investigation of the first-reported barrierless reaction between two closed-shell molecules [J. Chem. Phys. 127, 101101 (2007)] is presented. The translational energy and angular distributions of two product channels, HF+CH(2)SFCH(3) and F+CH(3)SFCH(3), determined at several collision energies, have been analyzed to reveal the dynamics of the studied reaction. Detailed analysis of the experimental and computational results supports the proposed reaction mechanism involving a short-lived F-F-S(CH(3))(2) intermediate, which can be formed without any activation energy. Other possible reaction mechanisms have been discriminated. The decay of the intermediate and competition between the two product channels have been discussed. (c) 2008 American Institute of Physics.
Barrierless reactions between two closed-shell molecules. II. Dynamics of F(2)+CH(3)SSCH(3) reaction
(2009-01-07)
Shao, Hua-Chieh
;
Xie, Tingxian
;
Lu, Yu-Ju
;
Chang, Chih-Hsuan
;
Pan, Jun-Wei
A second example of a barrierless reaction between two closed-shell molecules is reported. The reaction F(2)+CH(3)SSCH(3) has been investigated with crossed molecular beam experiments and ab initio calculations. Compared with previous results of the F(2)+CH(3)SCH(3) reaction [J. Chem. Phys. 127, 101101 (2007); J. Chem. Phys. 128, 104317 (2008)], a new product channel leading to CH(3)SF+CH(3)SF is observed to be predominant in the title reaction, whereas the anticipated HF+C(2)H(5)S(2)F channel is not found. In addition, the F+C(2)H(6)S(2)F product channel, the analog to the F+C(2)H(6)SF channel in the F(2)+CH(3)SCH(3) reaction, opens up at collision energies higher than 4.3 kcal/mol. Angular and translational energy distributions of the products are reported and collision energy dependences of the reaction cross section and product branching ratio are shown. The reaction barrier is found to be negligible (< 1 kcal/mol). Multireference ab initio calculations suggest a reaction mechanism involving a short-lived intermediate which can be formed without activation energy.
Barrierless reactions between two closed-shell molecules. II. Dynamics of F-2+CH3SSCH3 reaction
(2009-01-07)
Shao, Hua-Chieh
;
Xie, Tingxian
;
Lu, Yu-Ju
;
Chang, Chih-Hsuan
;
Pan, Jun-Wei
A second example of a barrierless reaction between two closed-shell molecules is reported. The reaction F-2+CH3SSCH3 has been investigated with crossed molecular beam experiments and ab initio calculations. Compared with previous results of the F-2+CH3SCH3 reaction [J. Chem. Phys. 127, 101101 (2007); J. Chem. Phys. 128, 104317 (2008)], a new product channel leading to CH3SF+CH3SF is observed to be predominant in the title reaction, whereas the anticipated HF+C2H5S2F channel is not found. In addition, the F+C2H6S2F product channel, the analog to the F+C2H6SF channel in the F-2+CH3SCH3 reaction, opens up at collision energies higher than 4.3 kcal/mol. Angular and translational energy distributions of the products are reported and collision energy dependences of the reaction cross section and product branching ratio are shown. The reaction barrier is found to be negligible (< 1 kcal/mol). Multireference ab initio calculations suggest a reaction mechanism involving a short-lived intermediate which can be formed without activation energy.
Dynamics of the F(2) Reaction with Propene: The Effect of Methyl Substitution
(2009-04-23)
Fang, Jing-Wen
;
Xie, Tingxian
;
Chen, Hsueh-Ying
;
Lu, Yu-Ju
;
Lee, Yuan T.
The reaction of F(2) + C(3)H(6) has been investigated with the crossed molecular beam technique. The only observed primary product channel is F + C(3)H(6)F while the HF + C(3)H(5)F channel cannot be found. The reaction cross section was measured as a function of collision energy and the reaction threshold was determined to be 2.4 +/- 0.3 kcal/mol. Compared to the reaction threshold of the F(2) + C(2)H(4) reaction, the methyl substitution effectively reduces the reaction threshold by about 3 kcal/mol. The product time-of-flight spectra and angular distributions were measured and analyzed. The angular distribution displays strongly backward, indicating that the reaction is much faster than rotation. All experimental results support a rebound reaction mechanism, which agrees with the structure of the calculated transition state. The transition state geometry also suggests an early barrier; such dynamics is consistent with the observed small kinetic energy release of the products. Except for the different values of the reaction thresholds, the dynamics of the F(2) + C(2)H(4) and F(2) + C(3)H(6) reactions are remarkably similar.
Dynamics of the F(2) reaction with the simplest pi-bonding molecule
(2008-05-14)
Lu, Yu-Ju
;
Xie, Tingxian
;
Fang, Jing-Wen
;
Shao, Hua-Chieh
;
Lin, Jim J.
The reaction of F(2)+C(2)H(4) has been investigated with crossed molecular beam experiments and high level ab initio calculations. For a wide range of collision energies up to 11 kcal/mol, only one reaction channel could be observed in the gas phase. The primary products of this channel were identified as F+CH(2)CH(2)F. The experimental reaction threshold of collision energy was determined to be 5.5 +/- 0.5 kcal/mol. The product angular distribution was found to be strongly backward, indicating that the reaction time scale is substantially shorter than rotation. The calculated transition state structure suggests an early barrier; such dynamics is consistent with the small product kinetic energy release measured in the experiment. All experimental results consistently support a rebound reaction mechanism, which is suggested by the calculation of the intrinsic reaction coordinate. This work provides a clear and unambiguous description of the reaction dynamics, which may help to answer the question why the same reaction produces totally different products in the condensed phase. (C) 2008 American Institute of Physics.
Dynamics of the F-2 Reaction with Propene: The Effect of Methyl Substitution
(2009-04-23)
Fang, Jing-Wen
;
Xie, Tingxian
;
Chen, Hsueh-Ying
;
Lu, Yu-Ju
;
Lee, Yuan T.
The reaction of F-2 + C3H6 has been investigated with the crossed molecular beam technique. The only observed primary product channel is F + C3H6F while the HF + C3H5F channel cannot be found. The reaction cross section was measured as a function of collision energy and the reaction threshold was determined to be 2.4 +/- 0.3 kcal/mol. Compared to the reaction threshold of the F-2 + C2H4 reaction, the methyl substitution effectively reduces the reaction threshold by about 3 kcal/mol. The product time-of-flight spectra and angular distributions were measured and analyzed. The angular distribution displays strongly backward, indicating that the reaction is much faster than rotation. All experimental results support a rebound reaction mechanism, which agrees with the structure of the calculated transition state. The transition state geometry also suggests an early barrier; such dynamics is consistent with the observed small kinetic energy release of the products. Except for the different values of the reaction thresholds, the dynamics of the F-2 + C2H4 and F-2 + C3H6 reactions are remarkably similar.