Reservoir Species and Coupling of the Cycles

Both nitric acid (HN03) and hydrogen chloride (HC1) are relatively stable in the stratosphere and some fraction of each migrates back to and is removed from the troposphere by precipitation. 

A reactive species can also be temporarily removed from a catalytic cycle and be stored in a reservoir species, which itself is relatively unreactive but is not actually removed from the atmosphere. One of the most important reservoir species in the stratosphere is chlorine nitrate (C10N02), formed by 

Lifetime of the Reservoir Species CI0NO2 and HCI Chlorine nitrate (C10N02) photodissociates back to CIO its lifetime against photolysis is tqonoi =/cioNOa-the midstratosphere (15-30 km), y ciONOi - 5 x 10-5s so tciono, 5h. 

Any process that even modestly shifts the balance away from the reservoir species to CIO can have a large impact on ozone depletion. 

In the midlatitude lower stratosphere the concentration of CIO is actually controlled by the amount of CIONO2 present  

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Reservoir Species and Coupling of the Cycles 180 Stratospheric Species Observations and Predictions 184... 

The existence of reservoir species is central to the ozone depletion cycles. In every cycle a reactive free radical can be temporarily sequestered as a relatively unreactive reservoir species. In fact, HCI and CIONO2 together store as much as 99% of the active chlorine. Thus only a small change in the abundance of reservoir species can have a profound effect on the catalytic efficiency of a cycle. The importance of relative concentrations in determining the predominance of different reactions in the ozone depletion cycles can be illustrated in the case of CIO, cycles. Above 20 km, CIO, Cycle 1 is a dominant contributor to ozone loss. At lower altitudes where atomic oxygen levels are significantly lower, other cycles, which involve coupling with HO, and NO, become important ... 

The CIO , and NO , cycles are strongly coupled through the reservoir species CIONO2. The steady-state concentration of CIO results from a balance between production by reaction 4.34 and photolysis by reaction 4.35,... 

The coupling of a static PF extractor to a fluori-meter has been performed primarily to develop an independent matrix extraction method allowing the extraction kinetics to be monitored. This approach has been followed with a view to determining the number of static extraction cycles required for quantitative extraction of the analytes, irrespective of the kind of matrix concerned and whether the species concentrations in it were known. The extract obtained after each cycle is driven to a graduated reservoir from which it is aspirated into a flow-injection manifold connected to the fluorimeter. 

Palladium-catalyzed carbon-carbon cross-coupling reactions are among the best studied reactions in recent decades since their discovery [102, 127-130], These processes involve molecular Pd complexes, and also palladium salts and ligand-free approaches, where palladium(O) species act as catalytically active species [131-135]. For example, the Heck reaction with aryl iodides or bromides is promoted by a plethora of Pd(II) and Pd(0) sources [128, 130], At least in the case of ligand-free palladium sources, the involvement of soluble Pd NPs as a reservoir for catalytically active species seems very plausible [136-138], Noteworthy, it is generally accepted that the true catalyst in the reactions catalyzed by Pd(0) NPs is probably molecular zerovalent species detached from the NP surface that enter the main catalytic cycle and subsequently agglomerate as N Ps or even as bulk metal. 

Hemnann et have indicated that the standard palladacycle trans-di(fju-acetato)-bis[o-(di-o-tolylphosphino)benzyl]-dipaUadium(II) (A) might be a catalyst precursor to active palladium(O) complexes (Scheme 41). In other words, the palladacycle may act as a thermally stable reservoir for the real catalytic species, which is released by heterolytic Pd—C bond cleavage and is activated by subsequent reduction. If this is the acmal case a tfaditional catalytic cycle via Pd(0)/Pd(II) has to be postulated also with palladacycles. In addition, for cross-coupling and amination reactions there is strong evidence for the reduction mechanism of phosphapaUadacycle A into a Pd(0) species.f ... 

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