Browsing by Author "Song, Di"

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Anharmonic Rice-Ramsperger-Kassel-Marcus (RRKM) and product branching ratio calculations for the partially deuterated protonated water dimers: Dissociation and isomerization
(2013-03-14)
Song, Di
;
Su, Hongmei
;
Kong, Fan-ao
;
Lin, Sheng-Hsien
;
應用化學系分子科學碩博班
Partially deuterated protonated water dimers, H2O center dot H+ center dot D2O, H2O center dot D+ center dot HDO, and HDO center dot H+ center dot HDO, as important intermediates of isotopic labeled reaction of H3O+ + D2O, undergo direct dissociation and indirect dissociation, i.e., isomerization before the dissociation. With Rice-Ramsperger-Kassel-Marcus theory and ab initio calculations, we have computed their dissociation and isomerization rate constants separately under the harmonic and anharmonic oscillator models. On the basis of the dissociation and isomerization rate constants, branching ratios of two primary products, [HD2O+]/[H2DO+], are predicted under various kinetics models with the harmonic or anharmonic approximation included. The feasible kinetics model accounting for experimental results is shown to include anharmonic effect in describing dissociation, while adopting harmonic approximation for isomerization. Thus, the anharmonic effect is found to play important roles affecting the dissociation reaction, while isomerization rates are shown to be insensitive to whether the anharmonic or harmonic oscillator model is being applied. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4794152]
Anharmonic RRKM Calculation for the Dissociation of (H(2)O)(2)H(+) and Its Deuterated Species (D(2)O)(2)D(+)
(2010-09-23)
Song, Di
;
Su, Hongmei
;
Kong, Fan-ao
;
Lin, Sheng-Hsien
;
應用化學系分子科學碩博班
Investigations on the dissociation kinetics of hydrated protonium ions, (H(2)O)(2)H(+) and their deuterated species (H(2)O)(2)D(+), are reported based on the harmonic and anharmonic oscillator model using the transition state theory and ab initio calculations. We find that the dissociation of (H(2)O)(2)H(+) and (D(2)O)(2)D(+) exhibits a distinct threshold behavior due to the existence of activation energies. Moreover, the deviation between the harmonic and anharmonic dissociation rate constants becomes larger in the high energy or temperature range, with the rate constants becoming unreasonably large under the harmonic oscillator model. The isotope effect is found to become more distinct but only in the case of the anharmonic oscillator model. These results show that the anharmonic Rice-Ramsperger-Kassel-Marcus (RRKM) theory can provide a reasonably good description for the dissociation of (H(2)O)(2)H(+) and (D(2)O)(2)D(+). Furthermore, a theoretical model to demonstrate the principle of vibrational predissociation spectroscopy (VPS) is established from the viewpoint of RRKM theory and applied in determining the experimental conditions and understanding the role of the dissociation rate constant k(E) played in the VPS experiment, using (H(2)O)(2)H(+) and (H(2)O)(2)D(+) as examples.
Anharmonic RRKM Calculation for the Dissociation of (H2O)(2)H+ and Its Deuterated Species (D2O)(2)D+
(2010-09-23)
Song, Di
;
Su, Hongmei
;
Kong, Fan-ao
;
Lin, Sheng-Hsien
;
應用化學系分子科學碩博班
Investigations on the dissociation kinetics of hydrated protonium ions, (H2O)(2)H+ and their deuterated species (H2O)(2)D+, are reported based on the harmonic and anharmonic oscillator model using the transition state theory and ab initio calculations. We find that the dissociation of (H2O)(2)H+ and (D2O)(2)D+ exhibits a distinct threshold behavior due to the existence of activation energies. Moreover, the deviation between the harmonic and anharmonic dissociation rate constants becomes larger in the high energy or temperature range, with the rate constants becoming unreasonably large under the harmonic oscillator model. The isotope effect is found to become more distinct but only in the case of the anharmonic oscillator model. These results show that the anharmonic Rice-Ramsperger-Kassel-Marcus (RRKM) theory can provide a reasonably good description for the dissociation of (H2O)(2)H+ and (D2O)(2)D+. Furthermore, a theoretical model to demonstrate the principle of vibrational predissociation spectroscopy (VPS) is established from the viewpoint of RRKM theory and applied in determining the experimental conditions and understanding the role of the dissociation rate constant k(E) played in the VPS experiment, using (H2O)(2)H+ and (H2O)(2)D+ as examples.
Neutral Dissociation of Superexcited Oxygen Molecules in Intense Laser Fields
(2010-03-11)
Song, Di
;
Azarm, Ali
;
Kamali, Yousef
;
Liu, Kai
;
Xia, Andong
Superexcited States (SESs) of oxygen molecules and their neutral dissociation processes have been studied both experimentally and theoretically using intense femtosecond laser. We find that at the laser Intensity of similar to 2 x 10(14) W/cm(2), ultrashort laser pulse causes neutral dissociation of oxygen molecule by way of SESs. The dissociation products are the excited neutral oxygen atoms, which are observed that fluorescence,Spectroscopy. Laser power dependence of the fluorescence intensity shows that each molecule effectively absorbs ill average of tell laser photons. The total energy absorbed is sufficient to stimulate the molecule to many of the SESs The effect is equivalent to single photon excitation in the extreme-ultraviolet (XUV) region by synchrotron radiation (SR). Morse potential energy curves (PECs). are constructed for the SESs of O(2) molecules. In light of the PECs, predissociation mechanism is proposed for the neutral dissociation. Quasi-classical trajectroy (QCT) calculations show that the predissociation time is as short as 100 fs, which is consistent with our experimental measurement using ultrafast pump-probe technique