Bulk chemicals lifetimes

The vibrationally excited precursor AB/s/(fs) can decay not only via energy transfer to the bulk but also via a chemical transformation (desorption of B and reaction with the formation of D and C/s/). These chemical processes can be characterized by the chemical lifetime Tch, which can be estimated in the framework of the statistical RRKM theory (see, e.g., Refs. [50, 51]) using the reaction parameters of reagents B and A/s/, precursor AB/s/, and transition complexes determined based on the results of quantum-chemical calculations. Such estimates were performed for many reactions of interest for the growth of metal oxide films [20]. It appeared that in the wide temperature range... 

Research and development in the field of fine chemicals differs considerably from bulk chemicals. Requirements for industrial success of a new process are different from bulk chemicals where the most important feature is cost performances. Although this feature is of course important for development of fine chemicals, two other main parameters should be considered. First of all, time to market One must be ready to manufacture the product at the right time and for a limited period of time. The lifetime of most fine chemicals is much shorter than for bulk chemicals where 20 to 50 years is standard. Second, possible R D expenses are much lower than for bulk chemicals (Figure 1). 

Figure 2 Compared lifetimes and sales turnovers of fine chemicals versus bulk chemicals 1.2 Scientific Considerations...

Lifetimes of free atoms and radicals account for the degree of interaction of these particles with an ambient medium and with each other. Due to high reaction capability of active particles in gaseous and, especially, in liquid media, their lifetimes are rather small. In gaseous phase, at small pressures these lifetimes are determined by heterogeneous recombination of these particles on vessel walls and by interaction of these particles with an adsorbed layer. At high gas pressures, the lifetimes are determined by bulk recombination and chemical interaction with ambient molecules. 

These reactions have a characteristic free energy which implies the minimal voltage required. As discussed in section 4.1, an excited molecule is at the same time more easily oxidized and reduced than the ground state species. Reactions of excited molecules at electrodes are however practically unknown because their short lifetimes preclude the contact with the electrode when irradiation takes place in the bulk of the liquid. In practice the photoelectro-chemical reactions at non-excited electrodes are simply the thermal reactions of photoproducts. We shall give here two examples of such reactions. 

The importance of photochemical destruction in the 03s tropospheric budget implies that the lifetime of 03s is coupled to the chemical production and destruction of 03. Consequently, the simulated tropospheric budget of 03s may be affected directly by differences in the simulated chemistry. For example, simulations with a pre-industrial and a present-day emission scenario or with and without representation of NMHC chemistry will produce different estimates of the tropospheric oxidation efficiencies [39, 40]. However, our simulations indicate only small effects on the calculated 03s budget [6]. Figure 5 presents the simulated zonal distribution of 03s, the chemical destruction rate, of ozone (day"1) and the chemical loss of 03s (ppbv day 1) for the climatological April. The bulk of the 03s in the troposphere resides immediately below the tropopause, whereas the ozone chemical destruction rate maximizes in the tropical lower troposphere (Figures 5a and 5b). Hence, most 03s is photochemically destroyed between 15-25 °N and below 500 hPa. This region... 

Information on the hydration state of the Gd(III) chelate in solution is indispensable for the analysis of its proton relaxivity Several methods exist to determine q, though they are mostly applicable for other lanthanides than Gd(III). In the case of Eu(III) and Tb(III) complexes, the difference of the luminescence lifetimes measured in D20 and H20 can be related to the hydration number [15, 16]. For Dy(III) chelates, the lanthanide induced 170 chemical shift of the bulk water is proportional to the hydration number [17]. Different hydration states of the same chelate may also coexist in solution giving rise to a hydration equilibrium. Such an equilibrium can be assessed by UV-Vis measurements on the Eu(III) complex [18-20]. These techniques have been recently discussed [21]. 

Besides activity, durability of metal electrode nano-catalysts in acid medium has become one of the most important challenges of low-temperature fuel cell technologies. It has been reported that platinum electrode surface area loss significantly shortens the lifetime of fuel cells. In recent years, platinum-based alloys, used as cathode electrocatalysts, have been found to possess enhanced stability compared to pure Pt. The phenomenon is quite unusual, because alloy metals, such as Fe, Co and Ni, generally exhibit greater chemical and electrochemical activities than pure Pt. Some studies have revealed that the surface stmcture of these alloys differs considerably from that in the bulk A pure Pt-skin is formed in the outmost layer of the alloys due to surface segrega-... 

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