The one-color resonant two -photon ionization technique is employed to study jetcooled van der Waals(vdW)complex 0-xylene.N2 through the S0-S1 transition Around the band The spectra obtained exhibit rich information a...The one-color resonant two -photon ionization technique is employed to study jetcooled van der Waals(vdW)complex 0-xylene.N2 through the S0-S1 transition Around the band The spectra obtained exhibit rich information about the complex intermolecular vdW vibrational modes.We have tentatively assgned all the observed Spectral features.The structure of the complex has been obtained by calculation of the minimum energy structure.展开更多
The crystal phase, morphology and facet significantly influence the catalytic and photocat- alytic activity of TiO2. In view of optimizing the performance of catalysts, extensive efforts have been devoted to designing...The crystal phase, morphology and facet significantly influence the catalytic and photocat- alytic activity of TiO2. In view of optimizing the performance of catalysts, extensive efforts have been devoted to designing new sophisticate TiO2 structures with desired facet exposure, necessitating the understanding of chemical properties of individual surface. In this work, we have examined the photooxidation of methanol on TiO 2 （011）- （ 2 × 1 ） and TiO 2 （110） - （1 ×1） by two-photon photoemission spectroscopy （2PPE）. An excited state at 2.5 eV above the Fermi level （EF） on methanol covered （011） and （110） interface has been detected. The excited state is an indicator of reduction of TiO2 interface. Irradiation dependence of the excited resonance signal during the photochemistry of methanol on TiO2（011）-（2×1） and TiO2（110）-（1× 1） is ascribed to the interface reduction by producing surface hydroxyls. The reaction rate of photooxidation of methanol on TiO2（110）-（1× 1） is about 11.4 times faster than that on TiO2（011）-（2×1）, which is tentatively explained by the difference in the surface atomic configuration. This work not only provides a detailed characterization of the electronic structure of methanol/TiO2 interface by 2PPE, but also shows the importance of the surface structure in the photoreactivity on TiO2.展开更多
The electronic structure of methanol/TiO2（ll0） interface has been studied by photoemis- sion spectroscopy. The pronounced resonance which appears at 5.5 eV above the Fermi level in two-photon photoemission spectrosc...The electronic structure of methanol/TiO2（ll0） interface has been studied by photoemis- sion spectroscopy. The pronounced resonance which appears at 5.5 eV above the Fermi level in two-photon photoemission spectroscopy （2PPE） is associated with the photocatalyzed dissociation of methanol at fivefold coordinated Ti sites （Ti5c） on TiO2 （110） surface [Chem- ical Science 1, 575 （2010）]. To check whether this resonance signal arises from initial or intermediate states, photon energy dependent 2PPE and comparison between one-photon photoemission spectroscopy and 2PPE have been performed. Both results consistently sug- gest the resonance signal originates from the initially unoccupied intermediate states, i.e., excited states. Dispersion measurements suggest the excited state is localized. Time-resolved studies show the lifetime of the excited state is 24 fs. This work presents comprehensive char- acterization of the excited states on methanol/TiO2（110） interface, and provides elaborate experimental data for the development of theoretical methods in reproducing the excited states on TiO2 surfaces and interfaces.展开更多
The kinetics and dynamics of photocatalyzed dissociation of ethanol on TiO2（110） sur- face have been studied using the time-dependent and time-resolved femtosecond two-photon photoemission spectroscopy respectively,...The kinetics and dynamics of photocatalyzed dissociation of ethanol on TiO2（110） sur- face have been studied using the time-dependent and time-resolved femtosecond two-photon photoemission spectroscopy respectively, in order to unravel the photochemical properties of ethanol on this prototypical metal oxide surface. By monitoring the time evolution of the photoinduced excited state which is associated with the photocatalyzed dissociation of ethanol on Ti5c sites of Ti02（ll0）, the fractal-like kinetics of this surface photocatalytic reaction has been obtgined. The measured photocatalytic dissociation rate on reduced TiO2（l10） is faster than that on the oxidized surface. This is attributed to the larger defect density on the reduced surface which lowers the reaction barrier of the photocatalytic reaction at least methodologically. Possible reasons associated with the defect electrons for the acceleration have been discussed. By performing the interferometric two-pulse corre- lation on ethanol/TiO2（l10） interface, the ultrafast electron dynamics of the excited state has been measured. The analyzed lifetime （24 fs） of the excited state is similar to that on methanol/TiO2（110）. The appearance of the excited state provides a channel to mediate the electron transfer between the TiO2 substrate and its environment. Therefore studying its ultrafast electron dynamics may lead to the understanding of the microscopic mechanism of photocatalysis and photoelectrochemical energy conversion on TiO2.展开更多
A surface femtosecond two-photon photoemission （2PPE） spectrometer devoted to the study of ultrafast excited electron dynamics and photochemical kinetics on metal and metal oxide surfaces has been constructed. Low e...A surface femtosecond two-photon photoemission （2PPE） spectrometer devoted to the study of ultrafast excited electron dynamics and photochemical kinetics on metal and metal oxide surfaces has been constructed. Low energy photoelectrons are measured using a hemispherical electron energy analyzer with an imaging detector that allows us to detect the energy and the angular distributions of the photoelectrons simultaneously. A Mach-Zehnder interferom- eter was built for the time-resolved 2PPE （TR-2PPE） measurement to study ultrafast surface excited electron dynamics, which was demonstrated on the Cu（111） surface. A scheme for measuring time-dependent 2PPE （TD-2PPE） spectra has also been developed for studies of surface photochemistry. This technique has been applied to a preliminary study on the photochemical kinetics on ethanol/TiO2（110）. We have also shown that the ultrafast dynamics of photoinduced surface excited resonances can be investigated in a reliable way by combining the TR-2PPE and TD-2PPE techniques.展开更多
文摘The one-color resonant two -photon ionization technique is employed to study jetcooled van der Waals(vdW)complex 0-xylene.N2 through the S0-S1 transition Around the band The spectra obtained exhibit rich information about the complex intermolecular vdW vibrational modes.We have tentatively assgned all the observed Spectral features.The structure of the complex has been obtained by calculation of the minimum energy structure.
基金This work was supported the Natural Science Foundation of Liaoning Province （No.2015020242）, the National Natural Science Foundation of China （No.21203189 and No.21573225）, and the State Key Laboratory of Molecular Reaction Dynamics （No.ZZ- 2014-02）.
文摘The crystal phase, morphology and facet significantly influence the catalytic and photocat- alytic activity of TiO2. In view of optimizing the performance of catalysts, extensive efforts have been devoted to designing new sophisticate TiO2 structures with desired facet exposure, necessitating the understanding of chemical properties of individual surface. In this work, we have examined the photooxidation of methanol on TiO 2 （011）- （ 2 × 1 ） and TiO 2 （110） - （1 ×1） by two-photon photoemission spectroscopy （2PPE）. An excited state at 2.5 eV above the Fermi level （EF） on methanol covered （011） and （110） interface has been detected. The excited state is an indicator of reduction of TiO2 interface. Irradiation dependence of the excited resonance signal during the photochemistry of methanol on TiO2（011）-（2×1） and TiO2（110）-（1× 1） is ascribed to the interface reduction by producing surface hydroxyls. The reaction rate of photooxidation of methanol on TiO2（110）-（1× 1） is about 11.4 times faster than that on TiO2（011）-（2×1）, which is tentatively explained by the difference in the surface atomic configuration. This work not only provides a detailed characterization of the electronic structure of methanol/TiO2 interface by 2PPE, but also shows the importance of the surface structure in the photoreactivity on TiO2.
文摘The electronic structure of methanol/TiO2（ll0） interface has been studied by photoemis- sion spectroscopy. The pronounced resonance which appears at 5.5 eV above the Fermi level in two-photon photoemission spectroscopy （2PPE） is associated with the photocatalyzed dissociation of methanol at fivefold coordinated Ti sites （Ti5c） on TiO2 （110） surface [Chem- ical Science 1, 575 （2010）]. To check whether this resonance signal arises from initial or intermediate states, photon energy dependent 2PPE and comparison between one-photon photoemission spectroscopy and 2PPE have been performed. Both results consistently sug- gest the resonance signal originates from the initially unoccupied intermediate states, i.e., excited states. Dispersion measurements suggest the excited state is localized. Time-resolved studies show the lifetime of the excited state is 24 fs. This work presents comprehensive char- acterization of the excited states on methanol/TiO2（110） interface, and provides elaborate experimental data for the development of theoretical methods in reproducing the excited states on TiO2 surfaces and interfaces.
文摘The kinetics and dynamics of photocatalyzed dissociation of ethanol on TiO2（110） sur- face have been studied using the time-dependent and time-resolved femtosecond two-photon photoemission spectroscopy respectively, in order to unravel the photochemical properties of ethanol on this prototypical metal oxide surface. By monitoring the time evolution of the photoinduced excited state which is associated with the photocatalyzed dissociation of ethanol on Ti5c sites of Ti02（ll0）, the fractal-like kinetics of this surface photocatalytic reaction has been obtgined. The measured photocatalytic dissociation rate on reduced TiO2（l10） is faster than that on the oxidized surface. This is attributed to the larger defect density on the reduced surface which lowers the reaction barrier of the photocatalytic reaction at least methodologically. Possible reasons associated with the defect electrons for the acceleration have been discussed. By performing the interferometric two-pulse corre- lation on ethanol/TiO2（l10） interface, the ultrafast electron dynamics of the excited state has been measured. The analyzed lifetime （24 fs） of the excited state is similar to that on methanol/TiO2（110）. The appearance of the excited state provides a channel to mediate the electron transfer between the TiO2 substrate and its environment. Therefore studying its ultrafast electron dynamics may lead to the understanding of the microscopic mechanism of photocatalysis and photoelectrochemical energy conversion on TiO2.
文摘A surface femtosecond two-photon photoemission （2PPE） spectrometer devoted to the study of ultrafast excited electron dynamics and photochemical kinetics on metal and metal oxide surfaces has been constructed. Low energy photoelectrons are measured using a hemispherical electron energy analyzer with an imaging detector that allows us to detect the energy and the angular distributions of the photoelectrons simultaneously. A Mach-Zehnder interferom- eter was built for the time-resolved 2PPE （TR-2PPE） measurement to study ultrafast surface excited electron dynamics, which was demonstrated on the Cu（111） surface. A scheme for measuring time-dependent 2PPE （TD-2PPE） spectra has also been developed for studies of surface photochemistry. This technique has been applied to a preliminary study on the photochemical kinetics on ethanol/TiO2（110）. We have also shown that the ultrafast dynamics of photoinduced surface excited resonances can be investigated in a reliable way by combining the TR-2PPE and TD-2PPE techniques.
