Browsing by Author "Lu, Yu-Ju"

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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.
Crossed molecular beam studies on the reaction dynamics of O(D-1)+N2O
(2006-10-07)
Lu, Yu-Ju
;
Liang, Chi-Wei
;
Lin, Jim J.
;
應用化學系
;
Department of Applied Chemistry
The reaction of oxygen atom in its first singlet excited state with nitrous oxide was investigated under the crossed molecular beam condition. This reaction has two major product channels, NO+NO and N-2+O-2. The product translational energy distributions and angular distributions of both channels were determined. Using oxygen-18 isotope labeled O(D-1) reactant, the newly formed NO can be distinguished from the remaining NO that was contained in the reactant N2O. Both channels have asymmetric and forward-biased angular distributions, suggesting that there is no long-lived collision complex with lifetime longer than its rotational period. The translational energy release of the N-2+O-2 channel (f(T)=0.57) is much higher than that of the NO+NO channel (f(T)=0.31). The product energy partitioning into translational, rotational, and vibrational degrees of freedom is discussed to learn more about the reaction mechanism. The branching ratio between the two product channels was estimated. The (N2O)-N-46 product of the isotope exchange channel, O-18+(N2O)-N-44 -> O-16+(N2O)-N-46, was below the detection limit and therefore, the upper limit of its yield was estimated to be 0.8%. (c) 2006 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) + 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.
Dynamics of the F-2+CH3SCH3 reaction: A molecule-molecule reaction without entrance barrier
(2007-09-14)
Lu, Yu-Ju
;
Lee, Lance
;
Pan, Jun-Wei
;
Witek, Henryk A.
;
Lin, Jim J.
The F-2+CH3SCH3 reaction was studied with crossed molecular beam techniques and high level ab initio calculations. Significant reactivity was observed even at low collision energies, consistent with the negligible barrier height obtained from the ab initio calculations. All experimental findings are consistent with a weakly bound reaction intermediate of F-F-S(CH3)(2) structure, which possesses a special type of three-center four-electron bonding. Analogous intermediates can also explain the reactions of F-2 with CH3SH and CH3SSCH3.