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1.
Muonium-substituted free radicals are observed by muon spin rotation when positive muons are stopped in liquid substituted benzenes. From muon precession frequencies in high external magnetic fields the isotropic muon-electron hyperfine coupling constants Aμ are determined. 66 radicals are assigned to ortho-, meta- and para-substituted cyclohexadienyl-type radicals. Formally they are produced by addition of the light hydrogen isotope muonium to 24 mono-substituted benzenes. The distribution of muons between radicals and diamagnetic molecules is suggested to be governed by radiolytical processes near the end-of-track of the thermalizing muon. 相似文献
2.
Reduction of CO 2 by direct one‐electron activation is extraordinarily difficult because of the ?1.9 V reduction potential of CO 2. Demonstrated herein is reduction of aqueous CO 2 to CO with greater than 90 % product selectivity by direct one‐electron reduction to CO 2.? by solvated electrons. Illumination of inexpensive diamond substrates with UV light leads to the emission of electrons directly into water, where they form solvated electrons and induce reduction of CO 2 to CO 2.?. Studies using diamond were supported by studies using aqueous iodide ion (I ?), a chemical source of solvated electrons. Both sources produced CO with high selectivity and minimal formation of H 2. The ability to initiate reduction reactions by emitting electrons directly into solution without surface adsorption enables new pathways which are not accessible using conventional electrochemical or photochemical processes. 相似文献
3.
The dependence of a sensor’s response to hydrogen on the temperature and hydrogen pressure in an indium oxide nanostructured film is measured. A theory of sensor’s response to reducing gases in nanostructured semiconducting oxides with high concentrations of electrons in the conduction band is developed (using the example of In2O3). It is shown that the capture of conduction electrons by adsorbed oxygen redistributes the electrons in nanoparticles and reduces the surface electron density and the conductivity of a system; the conductivity is proportional to the electron density in nanoparticle contacts, i.e., to the surface electron density. It is found that atomic oxygen ions react with reducing gases (H2, CO) during adsorption of the latter: electrons are released and enter the volumes of nanoparticles; the conductivity of the system grows, creating the sensory effect. Using a model developed earlier to describe the distribution of conduction electrons in a semiconductor nanoparticle, a kinetic scheme corresponding to the above scenario is built and corresponding equations are solved. As a result, a theoretical dependence of a sensor’s sensitivity to temperature is found that describes the experimental data well. 相似文献
4.
Cross sections for radiative Coulomb capture of muons in hydrogen are shown to be enhanced by two orders of magnitude for muon energies in the neighbourhood of 2.8 keV. This effect has not been recognised earlier and has important consequences for negative muon physics as shown. 相似文献
5.
Exposure of 1,1-dimethylallene to a beam of spin-polarised, positive muons resulted in the effective addition of muonium atoms to the central carbon atom, giving the muonated 1,1-dimethylallyl radical, Me 2CCMu-⋯H 2, and to the methylene carbon atom, giving the vinyl radical, Me 2C⋯CH 2Mu. The muon—electron hyperfine coupling constants in these radicals, and their temperature dependences, are compared with ESR data for related protic radicals. 相似文献
6.
Spectroscopic characterization of neutral highly-coordinated compounds is essential in fundamental and applied research, but has been proven to be a challenging experimental target because of the difficulty in mass selection. Here, we report the preparation and size-specific infrared-vacuum ultraviolet (IR-VUV) spectroscopic identification of group-3 transition metal carbonyls Sc(CO) 7 and TM(CO) 8 (TM=Y, La) in the gas phase, which are the first confinement-free neutral heptacarbonyl and octacarbonyl complexes. The results indicate that Sc(CO) 7 has a C2v structure and TM(CO) 8 (TM=Y, La) have a D4h structure. Theoretical calculations predict that the formation of Sc(CO) 7 and TM(CO) 8 (TM=Y, La) is both thermodynamically exothermic and kinetically facile in the gas phase. These highly-coordinated carbonyls are 17-electron complexes when only those valence electrons that occupy metal−CO bonding orbitals are considered, in which the ligand-only 4b 1u molecular orbital is ignored. This work opens new avenues toward the design and chemical control of a large variety of compounds with unique structures and properties. 相似文献
7.
Muonium is a light isotope of hydrogen, so light that in strong hydrogen bonds its zero-point energy is close to or above the energy barrier; this favours the formation of symmetrical muonium bonds. In water, muons will exist as Mu(H 2O) 6+ in contrast to H(H 2O) 4+; the stability of this species will slow the exchange of Mu and H. With alkenes and alkynes, muons will preferentially form non-classical complexes because of their lower zero-point energy in weak bonds: in liquids, a muon will attach two molecules via a symmetrical muonium bond. 相似文献
8.
In order to realize the sulfur and water resistance and facilitate the CO oxidation reactions,the effects of strain on the adsorption of CO,O 2,SO 2 and H 2O molecules on Ni single-atom-catalyst supported by single-carbon-vacancy graphene(Ni-SG) have been studied based on first principles calculations.It shows that the compressive strain increases the adsorption energies of all above mentioned molecules on Ni-SG,where SO 2 is adsorbed more strongly on Ni-S... 相似文献
9.
Infrared light driven photocatalytic reduction of atmospheric CO 2 is challenging due to the ultralow concentration of CO 2 (0.04 %) and the low energy of infrared light. Herein, we develop a metallic nickel-based metal–organic framework loaded with Pt (Pt/Ni-MOF), which shows excellent activity for thermal-photocatalytic conversion of atmospheric CO 2 with H 2 even under infrared light irradiation. The open Ni sites are beneficial to capture and activate atmospheric CO 2, while the photogenerated electrons dominate H 2 dissociation on the Pt sites. Simultaneously, thermal energy results in spilling of the dissociated H 2 to Ni sites, where the adsorbed CO 2 is thermally reduced to CO and CH 4. The synergistic interplay of dual-active-sites renders Pt/Ni-MOF a record efficiency of 9.57 % at 940 nm for converting atmospheric CO 2, enables the procurement of CO 2 to be independent of the emission sources, and improves the energy efficiency for trace CO 2 conversion by eliminating the capture media regeneration and molecular CO 2 release. 相似文献
10.
The chemical behavior of positive muons in condensed phase ammonia has been investigated in order to elucidate the phase and temperature effects on the chemical and physical behavior of the muon and muonium formation in a simple binary compound. Diamagnetic muon yield (P D) was constant at 0.67±0.01 in both solid and liquid above 125 K. Muonium formation in solids were observed above 100 K with slow muonium spin relaxation. In liquids, the muonium yield and its spin relaxation rate showed temperature dependence. Addition of metallic sodium increased P D in liquids. 相似文献
11.
Globally reliable dipole oscillator strength distributions (DOSDs) have been constructed for ground state CO and CO 2 molecules; the DOSD for CO corresponds to photon energies greater than the electronic absorption threshold while that for CO 2 includes the infrared part of the spectra as well. The recommended DOSDs are used to evaluate the isotropic dipole—dipole dispersion energies for the COCO, COCO2 and CO2CO2 interactions as well as the molar refractivities, as a function of wavelength, and the dipole sums, Sk, k = 2(?1) -4, -6, -8, -10, for the two molecules. Pseudo-DOSD representations of the recommended DOSDs are provided which allow the efficient accurate evaluation of the dispersion energy coefficients C6 for the interaction of CO or CO 2 with a variety of other atoms and molecules. Previous results for C6 are found to be in disagreement with our recommended results for interactions involving CO 2. The results of this paper are used to give a reasonably general discussion of the difficulties associated with obtaining reliable results for C6 by using Padé approximant bounding methods. 相似文献
12.
Abstract Halogen atom transfer from CpMo(CO) 3X (X = Cl, Br and I) to CpW(CO) 3 ? forming CpMo(CO) 3 ? and CpW(CO) 3X occurs with a first-order dependence on the oxidant and the reductant. The rate constants show a very small dependence on the identity of X, suggesting a mechanism involving nucleophilic attack by CpW(CO) 3 ? on a carbonyl of CpMo(CO) 3X. 相似文献
13.
It is shown that the muonic K
/ K
intensity ratios in oxygen of oxides of third-row elements are correlated to the bond ionicities. A similar correlation is found in chlorine of corresponding compounds. These correlations confirm the dominant role played by the outer electrons of the bond partners in the coulomb capture mechanism of negative muons. 相似文献
14.
The absorption of CO and NO molecules by (H 2O) 20 clusters was studied by the method of molecular dynamics. In general, the clusters containing CO molecules are more stable mechanically, while the clusters with NO molecules are more stable against heating. The mobility of NO molecules in such clusters is higher than that of CO molecules. The total dipole moment, the static dielectric permeability, the number of active electrons in the clusters, and the specific number of hydrogen bonds between water molecules possess peak values when the number of doping molecules i = 6. IR absorption spectra mostly acquire a smooth shape at i > 6. Capture of CO and NO molecules by water cluster operates as anti-greenhouse effect. 相似文献
15.
Designing high-performance materials for CO 2 capture and conversion is of great significance to reduce the greenhouse effect and alleviate the energy crisis. The strategy of doping is widely used to improve activity and selectivity of the materials. However, it is unclear how the doping densities influence the materials’ properties. Herein, we investigated the mechanism of CO 2 capture, separation and conversion on MoS 2, MoSe 2 and Janus MoSSe monolayers with different boron doping levels using density functional theory (DFT) simulations. The results indicate that CO 2, H 2 and CH 4 bind weakly to the monolayers without and with single-atom boron doping, rendering these materials unsuitable for CO 2 capture from gas mixtures. In contrast, CO 2 binds strongly to monolayers doped with diatomic boron, whereas H 2 and CH 4 can only form weak interactions with these surfaces. Thus, the monolayers doped with diatomic boron can efficiently capture and separate CO 2 from such gas mixtures. The electronic structure analysis demonstrates that monolayers doped with diatomic doped are more prone to donating electrons to CO 2 than those with single-atom boron doped, leading to activation of CO 2. The results further indicate that CO 2 can be converted to CH 4 on diatomic boron doped catalysts, and MoSSe is the most efficient of the surfaces studied for CO 2 capture, separation and conversion. In summary, the study provides evidence for the doping density is vital to design materials with particular functions. 相似文献
16.
The lanthanide octacarbonyl anion complexes Ln(CO) 8− (Ln=Tm, Yb, Lu) were produced in the gas phase and detected by mass-selected infrared photodissociation spectroscopy in the carbonyl stretching-frequency region. By comparison of the experimental CO-stretching frequencies with calculated data, which are strongly red-shifted with respect to free CO, the Yb(CO) 8− and Lu(CO) 8− complexes were determined to possess octahedral ( Oh) symmetry and a doublet X 2A 2u (Yb) and singlet X 1A 1g (Lu) electronic ground state, whereas Tm(CO) 8− exhibits a D4h equilibrium geometry and a triplet X 3B 1g ground state. The analysis of the electronic structures revealed that the metal-CO attractive forces come mainly from covalent orbital interactions, which are dominated by [Ln(d)]→(CO) 8 π backdonation and [Ln(d)]←(CO) 8 σ donation (contributes ≈77 and 16 % to covalent bonding, respectively). The metal f orbitals play a very minor role in the bonding. The electronic structure of all three lanthanide complexes obeys the 32-electron rule if only those electrons that occupy the valence orbitals of the metal are considered. 相似文献
17.
An activation energy of E a=213.73 kJ mol –1 has been determined for the thermal decomposition of SmC 2O 4Cl to SmOCl, CO and CO 2. The result is predictable on the basis of the Kahwa-Mulokozi expression + for the activation energy and its extended interpretation.
Zusammenfassung Für den thermischen Zerfall von SmC2O4Cl in SmOCl, CO und CO2 wurde eine Aktivierungsenergie vonE
a=213.73 kJ.mol–1 ermittelt. Dieses Ergebnis kann auf der Basis der Kahwa-Mulokozi-Beziehung für die Aktivierungsenergie und ihrer erweiterten Interpretation vorhergesagt werden.
On study leave from the university of sokoto, Nigeria. 相似文献
18.
Pulsed laser flash photolysis of M(CO) 6 (M = Cr, Mo, W) in aliphatic and aromatic hydrocarbon solutions (solvent = n-C 7H 16 and C 6H 5X (X = F, Cl, H, CH 3)) produces (solvent)M(CO) 5 transients, which then react with Lewis bases (L; 1-hexene, piperidine, 2-picoline, pyridine) to afford LM(CO) 5 products. The solvent-displacement process has been studied at variable pressures to 150 MPa, and volumes of activation for this process have been determined. These volumes of activation are sensitive to the identity of the coordinated solvent and suggest that bonding of chlorobenzene to Cr takes place via a lone pair of electrons on Cl, but through an isolated olefinic linkage for benzene, fluorobenzene and toluene. Observed volumes of activation also are consistent with the accessibility of an interchange mechanism for solvent displacement of n-heptane and with a dissociative solvent displacement mechanism for the arenes and support an increasing contribution from the solvent interchange process vs. reversible solvent dissociation in the order of the increasing size of the metal atom, Cr<Mo ⋍ W. The observed ability of “[M(CO) 5]” to discriminate among various nucleophiles arises in part from the accessibility of these two competitive mechanisms. 相似文献
19.
We reported a strategy of carbon-negative H 2 production in which CO 2 capture was coupled with H 2 evolution at ambient temperature and pressure. For this purpose, carbonate-type Cu xMg yFe z layered double hydroxide (LDH) was preciously constructed, and then a photocatalysis reaction of interlayer CO 32− reduction with glycerol oxidation was performed as driving force to induce the electron storage on LDH layers. With the participation of pre-stored electrons, CO 2 was captured to recover interlayer CO 32− in presence of H 2O, accompanied with equivalent H 2 production. During photocatalysis reaction, Cu 0.6Mg 1.4Fe 1 exhibited a decent CO evolution amount of 1.63 mmol g −1 and dihydroxyacetone yield of 3.81 mmol g −1. In carbon-negative H 2 production process, it showed an exciting CO 2 capture quantity of 1.61 mmol g −1 and H 2 yield of 1.44 mmol g −1. Besides, this system possessed stable operation capability under simulated flu gas condition with negligible performance loss, exhibiting application prospect. 相似文献
20.
To date, the chemical conversion of organic pollutants into value-added chemical feedstocks rather than CO 2 remains a major challenge. Herein, we successfully developed a coupled piezocatalytic and advanced oxidation processes (AOPs) system for achieving the conversion of various organic pollutants to CO. The CO product stems from the specific process in which organics are first oxidized to carbonate through peroxymonosulfate (PMS)-based AOPs, and then the as-obtained carbonate is converted into CO by piezoelectric reduction under ultrasonic (US) vibration by using a Co 3S 4/MoS 2 catalyst. Experiments and DFT calculations show that the introduction of Co 3S 4 not only effectively promotes the transfer and utilization of piezoelectric electrons but also realizes highly selective conversion from carbonate to CO. The Co 3S 4/MoS 2/PMS system has achieved selective generation of CO in actual complex wastewater treatment for the first time, indicating its potential practical applicability. 相似文献
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