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1、Reaction resonances in the F+H2/HD reactions

We carried out a series of joint high-resolution crossed molecular beam experiment and accurate quantum dynamics studies to investigate dynamical resonances in the reactions. We observed Feshbach resonances in the F + H2 → HF(v’=2) + H reaction (Science 311, 1440 (2006)), also found that the forward scattering in the F + H2 → HF(v’=3) + H reaction is not caused by Feshbach or dynamical resonances, but rather by the slow-down mechanism over the centrifugal barrier in the exit channel (PNAS 105, 6227 (2008)).

Based on high-resolution experimental measurements on the F + HD reaction, we constructed the most accurate PES so far (known as FXZ PES) for the reaction system. Dynamics calculations on FXZ PES produced results in excellent agreement with the experiment, achieving a level of spectroscopic accuracy (PNAS 105, 12662 (2008)). Further theoretical studies predicted an oscillatory structure in collision energy dependence of differential cross sections (DCSs) at backward scattering direction, caused by partial wave resonances. In order to observe it, we performed a fully quantum state-resolved, crossed-molecular-beam experiment on the F + HD → HF( v’, j’) + D reaction with both beam sources (F and HD) cryogenically cooled to maximize resolution, and observed clearly such an oscillatory structure predicted by theory. This was the first time the rotational structures of a reaction resonance were observed in a chemical reaction. The theoretical results for the partial wave resonances are shifted to lower energy by 0.03 kcal/mol as compared to experiment, indicating a spectroscopic level of accuracy (Science 327, 1501 (2010)).

 

Collision energy-dependent differential cross sections for the backward scattering HF(v’=2) products summed over j’=0 to 3 for the F(2P3/2)+HD(j=0) reaction (Left);
Experimental and theoretical DCS of the HF(v’=2,j’=6) product of the F(2P3/2)+HD(j=0) reaction in the backward scattering direction (Right) (Science 327, 1501 (2010))

2、Non-adiabatic dynamics studies of the F+D2 and Cl+H2 reactions

F*/F + D2 → DF + D reaction is the paradigm for the non-adiabatic reaction system with spin-orbit couplings. We performed a high-resolution crossed-beam study for this reaction, and found that the reactivity of the excited state F* atom is considerably higher than the ground state F atom in the low collision energy region, indicating the breakdown of the Born-Oppenheimer (BO) approximation in the reaction at low collision energy as also verified by accurate quantum dynamics calculations (Science 317, 1061(2007)). In addition, we carried out a joint experimental and theoretical study for the Cl + H2 reaction. The reactivity of the spin-orbit excited state Cl* atom is much smaller than Cl atom at high collision energy, indicating the BO approximation works well in the Cl+H2 reaction at high collision energy (Science 322, 573 (2008)).


Experimental (A and B) and theoretical (C and D) three-dimensional D-atom product flux surface plots for the F/F*+D2(j=0) reaction at the collision energy of 0.48 kcal/mol;
(left, Science 317, 1061 (2007)).
(A) Collision-energy dependence of the differential cross sections in the backward direction for the Cl/Cl*+p-H2 reaction;
(B) The ratio of the cross sections shown in (A).
The red curve and the green circles indicates the results of theoretical calculations, whereas the diamonds indicates the experimental results (right, Science 322, 573 (2008))

3、State-to-state Differential Cross Sections for a four-atom reaction system

We have recently developed a quantum wave packet method to compute full-dimensional differential cross sections for four-atom reactions. The benchmark calculations were carried out for the prototypical HD + OH → H2O + D reaction on an accurate potential energy surface that yield DCSs in excellent agreement with those from a high-resolution, crossed–molecular beam experiment. This is the first time that DCS for a four-atom reaction was obtained from full-dimensional quantum scattering calculations, in excellent agreement with experiment, regarded as a milestone for chemical reaction dynamics (Science 333, 440 (2011)).


Experimental (A) and theoretical (B) 3D contour plots for the product translational energy and angle distributions for the OH+HD→H2O+D reaction at the collision energy of 6.9kcal/mol
(Science 333, 440 (2011))

4、Reaction dynamics of the H+HD/D2 reactions

The simplest triatomic H + H2 reaction is a prototypical system for chemical reaction dynamics. We observed the forward scattering product of H + HD → H2 + D reaction in a high-resolution crossed-molecular beam experiment. Accurate quantum dynamics calculations attributed the forward scattering to the time delay in the transition-state region resulting from the slow-down of the motion of the intermediate near the top of the barrier of the specific transition state (Nature 419, 281 (2002)). We also measured the collision energy dependence of rotational state-resolved DCSs for H + D2 → HD + D reaction, and observed oscillatory structures in the DCSs at the backward direction. The accurate quantum scattering calculations revealed that the oscillatory structures originate from the interferences of different quantized transition-state pathways, providing clear evidence that the intermediate transition states are quantized bottleneck states in the reaction(Science 300,1730 (2003)).

 

Experimental (A) and theoretical (B) three-dimensional product contour plots for the product translational energy and angle distributions for the H+HD→H2+D
reaction at the collision energy of 1.2eV;
(left, Nature 419, 281 (2002));
The probabilities density for the J=0 scattering wave function, sliced along the perpendicular to the minimum energy path at the saddle point,
plotted in the bending (vertical direction) and symmetric stretch (horizontal direction) normal coordinates.
Three density plots are shown in the figure at three collision energies: 0.40, 0.70, and 0.75 eV.
They are slightly above the three different quantum bottleneck states (0,00),(0,20), and (1,00) at the saddle point, correspondingly (right, Science 300,1730 (2003))

5、Photochemistry dynamics of methanol on TiO2 surface

We observed the first clear evidence that photocatalyzed splitting of methanol occurs only at Ti4+ surface sites with an OH bond cleavage on TiO2(110) using time-dependent two-photon photoemission (TD-2PPE) technique, in combination with scanning tunneling microscopy (STM). It was also found that the kinetics of photodissociation process is clearly not of single exponential, an important characteristic of this intrinsically heterogeneous photoreaction(Chem. Sci. 1, 575 (2010)). Recently, we investigated the photocatalysis of partially deuterated methanol (CD3OH) on TiO2(110) using a newly developed photocatalysis apparatus in combination with theoretical calculations. Preliminary experimental results showed that dissociation of CD3OH on TiO2(110) occurs in a stepwise manner in which the O-H dissociation proceeds first and is then followed by C-D dissociation to form formaldehyde(CD2O). However, the H and D atoms from bond cleavage do not combine to form hydrogen during irradiation, as transferring to the adjacent bridge-bonded oxygen (BBO) sites (J. Am. Chem. Soc. 134, 13366 (2012)). Further investigation with fully deuterated methanol (CD3OD) showed that D-atoms on BBO sites of the photocatalyzed methanol/TiO2(110) surface are mainly desorbed via D2O formation when the surface is heated, with only a small amount of D2 product formation via thermal recombination. Experimental results also indicated more BBO defects created by D2O recombinative desorption on the surface can make formation of D2 easier than D2O formation (J. Am. Chem. Soc. 135, 10206 (2013)).

 

Calculated energtics of the two-step dissociation of CD3OH on TiO2(110) surface; (left, J. Am. Chem. Soc. 134, 13366 (2012) );
Mechanism of molecular water and molecular hydrogen (deuterium) product from hydrogen atoms on TiO2(110) surface (right, J. Am. Chem. Soc.135, 10206 (2013))

6、Hydrogen Bonding dynamics in the Electronic Excited State

In 2010, we were invited to edit the first monograph in the excited-state hydrogen bonding research field: “Hydrogen Bonding and Transfer in the Excited State” (John Wiley & Sons Ltd.). 2012, we were invited to publish a review “Hydrogen Bonding in the Electronic Excited State” (Acc. Chem. Res., 45, 404, (2012)).


Hydrogen bonding dynamics processes in the electronic excited state (Acc. Chem. Res. 45, 404 (2012))

7、Research in fluorescent probes

Considering the specificity and reversibility of most enzymatic reactions, our group mimicked glutathione peroxidase activity, introduced organoselelium unit in the designing of fluorescent probes, and developed a fluorescent probe (Cy-PSe) for intracellular peroxynitrite based on the investigations on the quenching mechanism of the selenide-cyanine systems. We found that Cy-PSe was weakly fluorescent due to the excited state photo induced electron transfer (PET) from selenide unit to cyanine. However, oxidation of Cy-PSe in the selenium center by peroxynitrite suppressed the PET process and restored the fluorescence of the cyanine dye. A further study revealed that organotellurium compounds possessed the similar characteristics. By introducing organotellurium unit into cyanine dye, we then developed a reversible fluorescent probe, i.e. Cy-NTe, for peroxynitrite, and applied this probe in reversible imaging of peroxynitrite in living animals.

Proposed Reaction Mechanism, Structures of Cy-PSe and Its Oxidized Product Cy-PSeO (J. Am. Chem. Soc.133, 11030 (2011))

 

Proposed Reaction Mechanism, Structures of Cy-NTe and Its Oxidized Product Cy-NTeO ( J. Am. Chem. Soc.135, 7674 (2013))
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STATE KEY LABORATORY OF MOLECULAR REACTION DYNAMICS, DALIAN INSTITUTE OF CHEMICAL PHYSICS, CAS