Transition metal oxides excited states

The photoluminescence of lattice oxide ions of transition-metal oxides mixed or supported on conventional carriers has also been reported (160b). The luminescence is shown to occur from oxo complexes (M04)" (M = V, Mo, W, Cr) in which the transition-metal ion exists in a high oxidation state with a d° electronic configuration. Since the d orbitals of the transition-metal ion are not occupied and therefore the d-d transitions impossible, S0 -)-S charge-transfer electronic transitions occur in the oxo complexes upon absorption of light. The result is that an electron is transferred from a filled molecular orbital localized mainly on the O2 anions to a d orbital of the transition-metal ion. This leads to the formation of an excited singlet electronic state S, with two unpaired electrons, in which the total electron spin,... 

One deals with the ab initio description of electronic excited states. These include the attachment or removal of electrons, the account of direct or inverse photo-emission spectra, and the electron-hole excitations of the d -> d or charge transfer type. Advanced methods are presently under development to account for them the GW method, the SIC method, the LDA-I-U method, etc. However, they imply an increased computation cost, which is not routinely accessible for complex systems, such as most oxide surfaces. These methods are also expected to open the field of strongly correlated materials, among which transition metal oxides, which have important technological applications high-Tc superconductivity, giant magneto-resistance, etc. 

Better understanding of the ionization process in transition metal oxides requires more precise knowledge of their cationc states. Table 3 shows the preliminary results of the deMon calculations for VO+ and MoO+ ions [35], The ground states of ionized species are given in local and nonlocal approximation, cationic excited states are given only in a local description. They are tentatively ascribed to known ionization potentials... 

Zeolite catalysts incorporated or encapsulated with transition metal cations such as Mo, or Ti into the frameworks or cavities of various microporous and mesoporous molecular sieves were synthesized by a hydrothermal synthesis method. A combination of various spectroscopic techniques and analyses of the photocatalytic reaction products has revealed that these transition metal cations constitute highly dispersed tetrahedrally coordinated oxide species which enable the zeolite catalysts to act as efficient and effective photocatalysts for the various reactions such as the decomposition of NO into N2 and O2 and the reduction of CO2 with H2O into CH3OH and CH4. Investigations on the photochemical reactivities of these oxide species with reactant molecules such as NOx, hydrocarbonds, CO2 and H2O showed that the charge transfer excited triplet state of the oxides, i.e., (Mo - O ), - O ), and (Ti - O ), plays a significant role in the photocatalytic reactions. Thus, the present results have clearly demonstrated the unique and high photocatalytic reactivities of various microporous and mesoporous zeolitic materials incorporated with Mo, V, or Ti oxide species as well as the close relationship between the local structures of these transition metal oxide species and their photocatalytic reactivities. 

A variety of transition metal complexes including organometallics was subjected to an ac electrolysis in a simple undivided electrochemical cell, containing only two current-carrying platinum electrodes. The compounds (A) are reduced and oxidized at the same electrode. If the excitation energy of these compounds is smaller than the potential difference of the reduced (A ) and oxidized (A ) forms, back electron transfer may regenerate the complexes in an electronically excited state (A+ + A A + A). Under favorable conditions an electrochemiluminescence (eel) is then observed (A A + hv). A weak eel appeared upon electrolysis o t]jie following complexes Ir(III)-(2-phenylpyridine-C, N ) [Cu(I)(pyridine)i],... 

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