Partial yield spectroscopy

The partial yield of electrons in an energy window AE at a fixed final state energy E, as a function of photon energy, where E is fixed at < 5eV so that only secondary electrons are measured, is referred to as partial yield spectroscopy. When E > 5eV, although the technique is experimentally identical, it is used to study initial state and excitonic effects and is known as constant final state spectroscopy. 

GERISCHER The vacant surface states can be detected in the partial yield spectroscopy because the matrix element for an electronic transition from the core states to these surfaces states is large since they are concentrated at the same atom. What is the chance to observe an optical transition between occupied and vacant surface states ... 

SXE can also be excited by photons (fig. 4a), in which case the thickness of the investigated surface depth is increased by a few orders of magnitude. Conventional SXA of thin samples has in practice no surface sensitivity when compared to the other methods. The detection of the photon absorption can also be performed by measuring the yield of the emitted electrons so that the surface sensitivity may even be very high if the electrons are selected in a narrow energy window at low kinetic energy (partial yield spectroscopy). 

Fig. 8 Schematic representation of partial yield photoemission spectroscopy.

The photo-Kolbe reaction is the decarboxylation of carboxylic acids at tow voltage under irradiation at semiconductor anodes (TiO ), that are partially doped with metals, e.g. platinum [343, 344]. On semiconductor powders the dominant product is a hydrocarbon by substitution of the carboxylate group for hydrogen (Eq. 41), whereas on an n-TiOj single crystal in the oxidation of acetic acid the formation of ethane besides methane could be observed [345, 346]. Dependent on the kind of semiconductor, the adsorbed metal, and the pH of the solution the extent of alkyl coupling versus reduction to the hydrocarbon can be controlled to some extent [346]. The intermediacy of alkyl radicals has been demonstrated by ESR-spectroscopy [347], that of the alkyl anion by deuterium incorporation [344]. With vicinal diacids the mono- or bisdecarboxylation can be controlled by the light flux [348]. Adipic acid yielded butane [349] with levulinic acid the products of decarboxylation, methyl ethyl-... 

Scheme 2, vide infra for characterization of these structures) [15]. At an intermediate temperature of 500 °C, a 65/35 mixture of these two complexes is obtained [16]. The proposed structure is further confirmed by the mass balance analysis since hydrolysis or ethanolysis of the resulting solid yields the complementary amounts of neopentane, these are 2 and 3 equiv. of neopentane/Ta for [(=SiO)2Ta(= CHlBu)(CH2fBu)] and [(=SiO)Ta(= CH(Bu)(CH2fBu)2], respectively. Moreover, elemental analysis provides further information indeed, 4.2 wt % of Ta grafted onto sihca partially dehydroxylated at 700 °C corresponds to 0.22 mmol of Ta/g of sofid [ 17,18]. This is comparable to the amount of silanol present on this support (0.26 mmol OH/g), which shows that most of them have reacted during grafting (as observed by IR spectroscopy). 

Reaction of [Ir(Me)2cp (L)], L = PPh3, PMePh2, PMe2Ph, PMe3, with NOBF4 in CH2C12 affords [Ir(Me)2cp (NO)]BF4 and [Ir(Me)cp (NO)L](BF4)2, (71).95 EPR spectroscopy shows that the reaction proceeds through the IrlV intermediate. Electrochemical or chemical reduction of (71) yields the EPR-active species [Ir(Me)cp (NO)L](BF4), in which the unpaired electron is partially delocalized on the Ir nucleus. 

Shortly after the discovery of the hydrated electron. Hart and Boag [7] developed the method of pulse radiolysis, which enabled them to make the first direct observation of this species by optical spectroscopy. In the 1960s, pulse radiolysis facilities became quite widely available and attention was focussed on the measurement of the rate constants of reactions that were expected to take place in the spurs. Armed with this information, Schwarz [8] reported in 1969 the first detailed spur-diffusion model for water to make the link between the yields of the products in reaction (7) at ca. 10 sec and those present initially in the spurs at ca. 10 sec. This time scale was then only partially accessible experimentally, down to ca. 10 ° sec, by using high concentrations of scavengers (up to ca. 1 mol dm ) to capture the radicals in the spurs. From then on, advancements were made in the time resolution of pulse radiolysis equipment from microseconds (10 sec) to picoseconds (10 sec), which permitted spur processes to be measured by direct observation. Simultaneously, the increase in computational power has enabled more sophisticated models of the radiation chemistry of water to be developed and tested against the experimental data. 

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