Using a combination of the Monte Carlo models of fast electrons, of molecular ions (N+) and of atomic species (N^+, Nf), the influence of the discharge pressure (P) and voltage (Vc) on the energy distributio...Using a combination of the Monte Carlo models of fast electrons, of molecular ions (N+) and of atomic species (N^+, Nf), the influence of the discharge pressure (P) and voltage (Vc) on the energy distributions of fast atomic species (N^+, Nf) produced by e^--N2s and N2^+- N2s dissociation reactions at the cathode in a nitrogen dc glow discharge was investigated. Both the angular distributions and the density distributions along the radius of the species (N^+, Nf) produced by the two dissociations at the cathode were calculated. The results show that: (1) there is an optimum discharge condition for P and Vc in order to obtain the species (N^+, Nf) at the cathode with high a density and energy, (2) when the voltage is above 800 V, the species (N^+, Nf) bombarding the cathode are mainly produced by the N^+-N2s dissociation, whereas when the voltage is below 300 V, they are mainly produced by the e-N2s dissociation, and (3) at high Voltages the incident angles of a considerable number of Nf into the cathode are quite small. The density of the species (N^+ Nf) at the cathode increases with the voltage, and when the pressure goes up to about 133 Pa, it decreases with the increasing pressure.展开更多
Interference effects on the photoionization cross sections between two neighbouring atoms are considered based on the coherent scattering of the ionized electrons by the two nuclei when their separation is less than o...Interference effects on the photoionization cross sections between two neighbouring atoms are considered based on the coherent scattering of the ionized electrons by the two nuclei when their separation is less than or comparable to the de Broglie wave length of the ionized electrons. As an example, the single atomic nitrogen ionization cross section and the total cross sections of two nitrogen atoms with coherently added photoionization amplitudes are calculated from the threshold to about А (1 А=0.1 nm) of the photon energy. The photoionization cross sections of atomic nitrogen are obtained by using the close-coupling R-matrix method. In the calculation 19 states are included. The ionization energy of the atomic nitrogen and the photoionization cross sections agree well with the experimental results. Based on the R-matrix results of atomic nitrogen, the interference effects between two neighbouring nitrogen atoms are obtained. It is shown that the interference effects are considerable when electrons are ionized just above the threshold, even for the separations between the two atoms are larger than two times of the bond length of N2 molecules. Therefore, in hot and dense samples, effects caused by the coherent interference between the neighbours are expected to be observable for the total photoionization cross sections.展开更多
Comprehensive Summary The activation of inert chemical bonds is an exciting area of research in chemistry because it enables the direct utilization of readily available starting materials and promotes atom-and step-ec...Comprehensive Summary The activation of inert chemical bonds is an exciting area of research in chemistry because it enables the direct utilization of readily available starting materials and promotes atom-and step-economic synthesis.Undoubtedly,selectively activating and transforming multiple inert chemical bonds is an even more intriguing and demanding task in synthetic chemistry.However,due to its inherent complexity and extreme challenges,this endeavour is rarely accomplished.We report a copper-mediated complete cleavage and selective transformation of multiple inert chemical bonds of three easily available feedstocks,i.e.,a sp^(2)C—H bond in indoles,three sp^(3)C—H bonds and one C—N bond in a methyl carbon atom in TMEDA,and the C≡N triple bond in CH_(3)CN.This reaction proceeds via tandem carbon and nitrogen atom transfer,and allows for the direct and efficient cyanation of indoles,presenting a simple and direct alternative for synthesizing 3-cyanoindoles.展开更多
Potassium-ion batteries(PIBs) hold great potential as an alternative to lithium-ion batteries due to the abundant reserves of potassium and similar redox potentials of K+/K and Li+/Li. Unfortunately, PIBs with carbona...Potassium-ion batteries(PIBs) hold great potential as an alternative to lithium-ion batteries due to the abundant reserves of potassium and similar redox potentials of K+/K and Li+/Li. Unfortunately, PIBs with carbonaceous electrodes present sluggish kinetics, resulting in unsatisfactory cycling stability and poor rate capability. Herein, we demonstrate that the synergistic effects of the enlarged interlayer spacing and enhanced capacitive behavior induced by the co-doping of nitrogen and sulfur atoms into a carbon structure(NSC) can improve its potassium storage capability. Based on the capacitive contribution calculations, electrochemical impedance spectroscopy, the galvanostatic intermittent titration technique, and density functional theory results, the NSC electrode is found to exhibit favorable electronic conductivity,enhanced capacitive adsorption behavior, and fast K+ ion diffusion kinetics. Additionally, a series of exsitu characterizations demonstrate that NSC exhibits superior structural stability during the(de)potassiation process. As a result, NSC displays a high reversible capacity of 302.8 mAh g-1 at 0.1 Ag-1 and a stable capacity of 105.2 m Ahg-1 even at 2 Ag-1 after 600 cycles. This work may offer new insight into the effects of the heteroatom doping of carbon materials on their potassium storage properties and facilitate their application in PIBs.展开更多
基金supported by the Natural Science Foundation of Hebei Province,China(No.A2006000123)
文摘Using a combination of the Monte Carlo models of fast electrons, of molecular ions (N+) and of atomic species (N^+, Nf), the influence of the discharge pressure (P) and voltage (Vc) on the energy distributions of fast atomic species (N^+, Nf) produced by e^--N2s and N2^+- N2s dissociation reactions at the cathode in a nitrogen dc glow discharge was investigated. Both the angular distributions and the density distributions along the radius of the species (N^+, Nf) produced by the two dissociations at the cathode were calculated. The results show that: (1) there is an optimum discharge condition for P and Vc in order to obtain the species (N^+, Nf) at the cathode with high a density and energy, (2) when the voltage is above 800 V, the species (N^+, Nf) bombarding the cathode are mainly produced by the N^+-N2s dissociation, whereas when the voltage is below 300 V, they are mainly produced by the e-N2s dissociation, and (3) at high Voltages the incident angles of a considerable number of Nf into the cathode are quite small. The density of the species (N^+ Nf) at the cathode increases with the voltage, and when the pressure goes up to about 133 Pa, it decreases with the increasing pressure.
基金Project supported by the National Natural Science Foundation of China (Grant No 10734140)the National Basic Research Program of China (Grant No 2007CB815105)
文摘Interference effects on the photoionization cross sections between two neighbouring atoms are considered based on the coherent scattering of the ionized electrons by the two nuclei when their separation is less than or comparable to the de Broglie wave length of the ionized electrons. As an example, the single atomic nitrogen ionization cross section and the total cross sections of two nitrogen atoms with coherently added photoionization amplitudes are calculated from the threshold to about А (1 А=0.1 nm) of the photon energy. The photoionization cross sections of atomic nitrogen are obtained by using the close-coupling R-matrix method. In the calculation 19 states are included. The ionization energy of the atomic nitrogen and the photoionization cross sections agree well with the experimental results. Based on the R-matrix results of atomic nitrogen, the interference effects between two neighbouring nitrogen atoms are obtained. It is shown that the interference effects are considerable when electrons are ionized just above the threshold, even for the separations between the two atoms are larger than two times of the bond length of N2 molecules. Therefore, in hot and dense samples, effects caused by the coherent interference between the neighbours are expected to be observable for the total photoionization cross sections.
基金support from the National Natural Science Foundation of China(Grant Nos.22378106,21878072,21706058,and 22002169)the Natural Science Foundation of Hunan Province(Grant No.2020JJ2011)the China Postdoctoral Science Foundation(No.2019M662774).
文摘Comprehensive Summary The activation of inert chemical bonds is an exciting area of research in chemistry because it enables the direct utilization of readily available starting materials and promotes atom-and step-economic synthesis.Undoubtedly,selectively activating and transforming multiple inert chemical bonds is an even more intriguing and demanding task in synthetic chemistry.However,due to its inherent complexity and extreme challenges,this endeavour is rarely accomplished.We report a copper-mediated complete cleavage and selective transformation of multiple inert chemical bonds of three easily available feedstocks,i.e.,a sp^(2)C—H bond in indoles,three sp^(3)C—H bonds and one C—N bond in a methyl carbon atom in TMEDA,and the C≡N triple bond in CH_(3)CN.This reaction proceeds via tandem carbon and nitrogen atom transfer,and allows for the direct and efficient cyanation of indoles,presenting a simple and direct alternative for synthesizing 3-cyanoindoles.
基金supported by the National Natural Science Foundation of China (51932011, 51972346, 51802356, and 51872334)Innovation-Driven Project of Central South University (2020CX024)the Fundamental Research Funds for the Central Universities of Central South University (2020zzts075)。
文摘Potassium-ion batteries(PIBs) hold great potential as an alternative to lithium-ion batteries due to the abundant reserves of potassium and similar redox potentials of K+/K and Li+/Li. Unfortunately, PIBs with carbonaceous electrodes present sluggish kinetics, resulting in unsatisfactory cycling stability and poor rate capability. Herein, we demonstrate that the synergistic effects of the enlarged interlayer spacing and enhanced capacitive behavior induced by the co-doping of nitrogen and sulfur atoms into a carbon structure(NSC) can improve its potassium storage capability. Based on the capacitive contribution calculations, electrochemical impedance spectroscopy, the galvanostatic intermittent titration technique, and density functional theory results, the NSC electrode is found to exhibit favorable electronic conductivity,enhanced capacitive adsorption behavior, and fast K+ ion diffusion kinetics. Additionally, a series of exsitu characterizations demonstrate that NSC exhibits superior structural stability during the(de)potassiation process. As a result, NSC displays a high reversible capacity of 302.8 mAh g-1 at 0.1 Ag-1 and a stable capacity of 105.2 m Ahg-1 even at 2 Ag-1 after 600 cycles. This work may offer new insight into the effects of the heteroatom doping of carbon materials on their potassium storage properties and facilitate their application in PIBs.