The ultrafast dynamics through conical intersections in 2,6-dimethylpyridine has been studied by femtosecond time-resolved photoelectron imaging coupled with time-resolved mass spectroscopy. Upon absorption of 266 nm ...The ultrafast dynamics through conical intersections in 2,6-dimethylpyridine has been studied by femtosecond time-resolved photoelectron imaging coupled with time-resolved mass spectroscopy. Upon absorption of 266 nm pump laser, 2,6-dimethylpyridine is excited to the S2 state with a ππ character from So state. The time evolution of the parent ion signals consists of two exponential decays. One is a fast component on a timescale of 635 fs and the other is a slow component with a timescale of 4.37 ps. Time-dependent photo- electron angular distributions and energy-resolved photoelectron spectroscopy are extracted from time-resolved photoelectron imaging and provide the evolutive information of S2 state. In brief, the ultrafast component is a population transfer from S2 to S1 through the S2/S1 conical intersections, the slow component is attributed to simultaneous IC from the S2 state and the higher vibrational levels of S1 state to So state, which involves the coupling of S2/S0 and S1/So conical intersections. Additionally, the observed ultrafast S2--＋S1 transition occurs only with an 18% branching ratio.展开更多
As a powerful and sensitive tool for the characterization of zeolite building units,UV Raman spectroscopy has been used to monitor interzeolite transformation from FAU to CHA and MFI zeolites.The results show that the...As a powerful and sensitive tool for the characterization of zeolite building units,UV Raman spectroscopy has been used to monitor interzeolite transformation from FAU to CHA and MFI zeolites.The results show that the behavior of double 6-membered rings(D6Rs)in the FAU zeolite framework plays an important role during the formation of the target product in the interzeolite transformation.For the transformation of FAU to CHA,because both zeolites contain the same D6R units,direct transformation occurs,in which the D6Rs were largely unchanged.In contrast,for the transformation of FAU to MFI,the D6Rs can be divided into two single 6-membered rings(S6Rs),which further assembled into the MFI structure.In this crystallization,5-membered rings(5Rs)are only observed in the MFI framework formation,suggesting that the basic building units in the transformation of FAU to MFI are S6Rs rather than 5Rs.These insights will be helpful for further understanding of the interzeolite transformation.展开更多
The ultrafast photoisomerization and excited-state dynamics of trans-4-methoxyazobenzene (trans-4-MAB) in solutions were investigated by femtosecond transient absorption spectroscopy and quantum chemistry calculations...The ultrafast photoisomerization and excited-state dynamics of trans-4-methoxyazobenzene (trans-4-MAB) in solutions were investigated by femtosecond transient absorption spectroscopy and quantum chemistry calculations. After being excited to the S2 state, the two-dimensional transient absorptions spectra show that cis-4-MAB is produced and witnessed by the permanent positive absorption in 400-480 nm. Three decay components are determined to be 0.11, 1.4 and 2.9 ps in ethanol, and 0.16, 1.5 and 7.5 ps in ethylene glycol, respectively. The fast component is assigned to the internal conversion from the S2 to S1 state. The other relaxation pathways are correlated with the decay of the S1 state via internal conversion and isomerization, and the vibrational cooling of the hot S0 state of the cis-isomer. Comparing of the dynamics in different solvents, it is demonstrated that the photoisomerization pathway undergoes the inversion mechanism rather than the rotation mechanism.展开更多
The dynamic NMR （DNMR） method was used to detect kinetic parameters of the molecular exchange process between monomers in bulk solution and those in the micelle for Gemini surfactants, 12-s-12 and 14-s-14 （s 2, 3 a...The dynamic NMR （DNMR） method was used to detect kinetic parameters of the molecular exchange process between monomers in bulk solution and those in the micelle for Gemini surfactants, 12-s-12 and 14-s-14 （s 2, 3 and 4）. The escape rate constant, k^- , was derived based on the simplified equations of DNMR theory, and the apparent activation energy of escape, Ea^- , was obtained based on the Arrhenius equation through temperature variation experiments. Results show that the orders of magnitude of k^- for 14-s-14 and 12-s-12 are respectively 10 and 103 s-1, Ea^- of 14-s-14 and 12-s-12 are respectively 54.04-73.64 and 33.42-47.09 kJ/rnol. Furthermore, k increases and Ea^- decreases with the spacer length growing. In combination with the rnicro-polarity measurements, it was revealed that molecules of 14-s-14 and 12-s-12 have to experience conformation changes when escaping from the rnicelles. The two-step molecular exchange mechanism for Gemini surfactants was therefore supported.展开更多
Time-resolved photoionization is a powerful experimental approach to unravel the excited state dynamics in isolated polyatomic molecules. Depending on species of the collected signals, different methods can be perform...Time-resolved photoionization is a powerful experimental approach to unravel the excited state dynamics in isolated polyatomic molecules. Depending on species of the collected signals, different methods can be performed: time-resolved ion yield spectroscopy (TR-IYS) and time-resolved photoelectron imaging (TR-PEI). In this review, the essential concepts linking photoionization measurement with electronic structure are presented, together with several important breakthroughs in experimentally distinguishing the oscillating wavepacket motion between different geometries. We illustrate how femtosecond TR-IYS and TR-PEI are employed to visualize the evolution of a coherent vibrational wavepacket on the excited state surface.展开更多
The mode specificity plays an important role in understanding the fundamental reaction dynamics. This work reports a theoretical study of the rotational mode specificity of the reactant CHD3(JK) in the prototypical hy...The mode specificity plays an important role in understanding the fundamental reaction dynamics. This work reports a theoretical study of the rotational mode specificity of the reactant CHD3(JK) in the prototypical hydrocarbon oxidation reaction O(3P)+CHD3→OH+CD3. The time-dependent quantum wave packet method combined with a seven-dimensional reduced model is employed to calculate the reaction probability on an accurate potential energy surface. The obtained reaction probability depends on the values of both K and Ktot with PKtot=K=0>PKtot=K=J>PKtot=J,K=0=PKtot=0,K=J. This observation can be well rationalized by the reactant alignment pictures. Rotational excitations of CHD3 up to the angular momentum quantum number J=4 have a very weak enhancement effect on the reaction except for the state (J=4, K=0). In addition, the rotationally excited states of CHD3 with K=0 promote the reaction more than those with K=J. The quantum dynamics calculations indicate that the K=0 enhancements are mainly caused by the contributions from the components with K=Ktot=0. The components correspond to the tumbling rotation of CHD3, which enlarges the range of the reactive initial attack angles.展开更多
Although the many-body expansion(MBE)approach is widely applied to estimate the energy of large systems containing weak interactions,it is inapplicable to calculating the energies of covalent or metal clusters.In this...Although the many-body expansion(MBE)approach is widely applied to estimate the energy of large systems containing weak interactions,it is inapplicable to calculating the energies of covalent or metal clusters.In this work,we propose an interaction manybody expansion(IMBE)to calculate the energy of atomic clusters containing covalent bonds.In this approach,the energy of a system is expressed as the sum of the energy of atoms and the interaction energy between the atom and its surrounding atoms.The IMBE method is first applied to calculate the energies of nitrogen clusters,in which the interatomic interactions are truncated to four-body terms.The results show that the IMBE approach could significantly reduce the energy error for nitrogen clusters compared with the traditional MBE method.The weak size and structure dependence of the IMBE error with respect to DFT calculations indicates the IMBE method has good potential application in estimating energy of large covalent systems.展开更多
基金supported by the National Natural Science Foundation of China(20973194)Project of Science & Technology from Chongqing Municipal Education Commission,China(KJ090626)Research Foundation of Chongqing University of Technology,China(2008ZD18)~~
基金This work was supported by the National Natural Science Foundation of China （No.10704083）,the Innovation Foundation of Chinese Academyof Sciences （No.KJCX1-YW-N30）, and the Public Science and Technology Program of Shenzhen （No.SY200806260026A）.
文摘The ultrafast dynamics through conical intersections in 2,6-dimethylpyridine has been studied by femtosecond time-resolved photoelectron imaging coupled with time-resolved mass spectroscopy. Upon absorption of 266 nm pump laser, 2,6-dimethylpyridine is excited to the S2 state with a ππ character from So state. The time evolution of the parent ion signals consists of two exponential decays. One is a fast component on a timescale of 635 fs and the other is a slow component with a timescale of 4.37 ps. Time-dependent photo- electron angular distributions and energy-resolved photoelectron spectroscopy are extracted from time-resolved photoelectron imaging and provide the evolutive information of S2 state. In brief, the ultrafast component is a population transfer from S2 to S1 through the S2/S1 conical intersections, the slow component is attributed to simultaneous IC from the S2 state and the higher vibrational levels of S1 state to So state, which involves the coupling of S2/S0 and S1/So conical intersections. Additionally, the observed ultrafast S2--＋S1 transition occurs only with an 18% branching ratio.
基金supported by the National Key R&D Program of China(2017YFB0702800)the National Natural Science Foundation of China(2152780065,91634201 and 21720102001)the Strategic Priority Research Program of Chinese Academy of Sciences(XDB17000000)~~
文摘As a powerful and sensitive tool for the characterization of zeolite building units,UV Raman spectroscopy has been used to monitor interzeolite transformation from FAU to CHA and MFI zeolites.The results show that the behavior of double 6-membered rings(D6Rs)in the FAU zeolite framework plays an important role during the formation of the target product in the interzeolite transformation.For the transformation of FAU to CHA,because both zeolites contain the same D6R units,direct transformation occurs,in which the D6Rs were largely unchanged.In contrast,for the transformation of FAU to MFI,the D6Rs can be divided into two single 6-membered rings(S6Rs),which further assembled into the MFI structure.In this crystallization,5-membered rings(5Rs)are only observed in the MFI framework formation,suggesting that the basic building units in the transformation of FAU to MFI are S6Rs rather than 5Rs.These insights will be helpful for further understanding of the interzeolite transformation.
基金supported by the National Natural Science Foundation of China(No.21603049,No.11674355,No.11705043,No.21327804,No.11364043)the Fundamental Research Funds for the Central Universities(No.JZ2015HGBZ0532)+1 种基金the Industry-UniversityResearch Fund of Hefei University of Technology Xuancheng Campus(No.XC2016JZBZ11)the Natural Science Foundation of Xinjiang Uygur Autonomous Region(No.2016D01A058)
文摘The ultrafast photoisomerization and excited-state dynamics of trans-4-methoxyazobenzene (trans-4-MAB) in solutions were investigated by femtosecond transient absorption spectroscopy and quantum chemistry calculations. After being excited to the S2 state, the two-dimensional transient absorptions spectra show that cis-4-MAB is produced and witnessed by the permanent positive absorption in 400-480 nm. Three decay components are determined to be 0.11, 1.4 and 2.9 ps in ethanol, and 0.16, 1.5 and 7.5 ps in ethylene glycol, respectively. The fast component is assigned to the internal conversion from the S2 to S1 state. The other relaxation pathways are correlated with the decay of the S1 state via internal conversion and isomerization, and the vibrational cooling of the hot S0 state of the cis-isomer. Comparing of the dynamics in different solvents, it is demonstrated that the photoisomerization pathway undergoes the inversion mechanism rather than the rotation mechanism.
基金supported by the National Natural Science Foundation of China (No.21375145)
文摘The dynamic NMR （DNMR） method was used to detect kinetic parameters of the molecular exchange process between monomers in bulk solution and those in the micelle for Gemini surfactants, 12-s-12 and 14-s-14 （s 2, 3 and 4）. The escape rate constant, k^- , was derived based on the simplified equations of DNMR theory, and the apparent activation energy of escape, Ea^- , was obtained based on the Arrhenius equation through temperature variation experiments. Results show that the orders of magnitude of k^- for 14-s-14 and 12-s-12 are respectively 10 and 103 s-1, Ea^- of 14-s-14 and 12-s-12 are respectively 54.04-73.64 and 33.42-47.09 kJ/rnol. Furthermore, k increases and Ea^- decreases with the spacer length growing. In combination with the rnicro-polarity measurements, it was revealed that molecules of 14-s-14 and 12-s-12 have to experience conformation changes when escaping from the rnicelles. The two-step molecular exchange mechanism for Gemini surfactants was therefore supported.
基金supported by the National Natural Science Foundation of China (No.21327804, No.21773299, No.91121006, No.21573279, No.11574351, No.11774385, No.11674355, No.21503270, and No.21303255)
文摘Time-resolved photoionization is a powerful experimental approach to unravel the excited state dynamics in isolated polyatomic molecules. Depending on species of the collected signals, different methods can be performed: time-resolved ion yield spectroscopy (TR-IYS) and time-resolved photoelectron imaging (TR-PEI). In this review, the essential concepts linking photoionization measurement with electronic structure are presented, together with several important breakthroughs in experimentally distinguishing the oscillating wavepacket motion between different geometries. We illustrate how femtosecond TR-IYS and TR-PEI are employed to visualize the evolution of a coherent vibrational wavepacket on the excited state surface.
基金supported by the National Natural Science Foundation of China (No.21773297 to Ming-hui Yang, No.21703210 to Rui Liu, and No.21603266 to Hong-wei Song)China Postdoctoral Science Foundation funded Project under Grant 2017M610492
文摘The mode specificity plays an important role in understanding the fundamental reaction dynamics. This work reports a theoretical study of the rotational mode specificity of the reactant CHD3(JK) in the prototypical hydrocarbon oxidation reaction O(3P)+CHD3→OH+CD3. The time-dependent quantum wave packet method combined with a seven-dimensional reduced model is employed to calculate the reaction probability on an accurate potential energy surface. The obtained reaction probability depends on the values of both K and Ktot with PKtot=K=0>PKtot=K=J>PKtot=J,K=0=PKtot=0,K=J. This observation can be well rationalized by the reactant alignment pictures. Rotational excitations of CHD3 up to the angular momentum quantum number J=4 have a very weak enhancement effect on the reaction except for the state (J=4, K=0). In addition, the rotationally excited states of CHD3 with K=0 promote the reaction more than those with K=J. The quantum dynamics calculations indicate that the K=0 enhancements are mainly caused by the contributions from the components with K=Ktot=0. The components correspond to the tumbling rotation of CHD3, which enlarges the range of the reactive initial attack angles.
基金supported by the National Natural Science Foundation of China(No.21773297,No.21973108,and No.21921004)supported by the National Natural Science Foundation of China(No.21805258)supported by the National Natural Science Foundation of China(No.21973107)。
文摘Although the many-body expansion(MBE)approach is widely applied to estimate the energy of large systems containing weak interactions,it is inapplicable to calculating the energies of covalent or metal clusters.In this work,we propose an interaction manybody expansion(IMBE)to calculate the energy of atomic clusters containing covalent bonds.In this approach,the energy of a system is expressed as the sum of the energy of atoms and the interaction energy between the atom and its surrounding atoms.The IMBE method is first applied to calculate the energies of nitrogen clusters,in which the interatomic interactions are truncated to four-body terms.The results show that the IMBE approach could significantly reduce the energy error for nitrogen clusters compared with the traditional MBE method.The weak size and structure dependence of the IMBE error with respect to DFT calculations indicates the IMBE method has good potential application in estimating energy of large covalent systems.
