Reaction mechanisms spectra predictions

To reveal the complete reaction mechanism, the reaction was investigated at lower temperatures. The product ion mass spectrum recorded at 100 K with O2 and CO in the ion trap (Fig. 1.63b) shows the appearance of the coadsorption complex Au2(C0)02 discussed above. This complex represents a key intermediate in the reaction mechanism of the catalytic oxidation of CO to CO2 as has been predicted in the earlier theoretical study [382]. The experimental evidence obtained so far demonstrates that O2 adsorption is likely to be the first step in the observed reaction mechanism. Subsequent CO coadsorption yields the observed intermediate (Fig. 1.63b) and finally the bare gold dimer ion must be reformed. The further strategy to reveal the full reaction mechanism consists in varying the available experimental parameters, i.e., reaction temperature and reactant partial pressures. This procedure leads to a series of kinetic traces similar to the one shown in Fig. 1.64b and c [33]. The goal then is to find one reaction mechanism that is able to fit all experimental kinetic data obtained under the various reaction conditions. This kinetic... 

Although we cannot directly detect HCaOH because it probably has a dissociative UV spectrum [14], we can detect another predicted reaction intermediate in some of our experiments. Mechanism A predicts that the CaH molecule will be present in the Broida oven, and with some oxidants we have detected it by laser-induced fluorescence. The CaH molecule is seen when carboxylic acids such as formic acid are used to make the monocar-boxylates such as Sr02CH [42]. Curiously, CaH is not detected [41] when water or alcohols such as CH3OH are used to make alkoxides such as CaOCH3. More experimental and theoretical work is necessary to establish the chemical mechanisms involved in the reactivity of the alkaline earth atoms. 

A critical point in the retrieving of the number of nuclear reactions in laser-solid experiments is that there is no control on the spectrum of the electrons accelerated in the interaction, as well as the acceleration mechanism is uncertain and difficult to fit in a predictable scheme. In most cases, the electron energy distribution is assumed to be Boltzmann-like and deconvolutions are performed starting from this assumption. 

Agreement of a spatially averaged quantity, such as a reaction rate and a temperature-programmed desorption spectrum, is often insufficient to test whether the underlying mechanisms and input in a molecular model are correct. Ideally, validation of molecular simulation predictions demands spatiotemporal data over a multitude of length and time scales. Unfortunately, such data are rarely available (see the membrane application example earlier). However, advances in scanning probe techniques start rendering such comparisons feasible. 

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