ABSTRACT
Phosphorus is a key and vital element for a diverse set of important biological molecules, being indispensable for life as we know. A deeper comprehension of its role in astrochemistry and atmospheric chemistry may aid in finding answers to how this element became available on Earth. The PO molecule is one of the main reservoirs of phosphorus in the interstellar medium (ISM), and a better understanding of the mechanisms and rate coefficients for its formation in the ISM is important for modelling its abundances. In this work, we perform multireference configuration interaction calculations on the formation of PO via the [Formula: see text] reaction, analyzing its potential energy surface and rate coefficients for the global reaction on both doublet and quartet states. We also perform DFT (M06-2X) and CCSD(T) calculations, in order to compare the results. We found that the OPO system possesses a high multiconfigurational character, making DFT and CCSD methodologies not suitable for its potential energy landscape calculation. The rate coefficients have been calculated using the master equation system solver (MESS) package, and the results compared to recent experimental data. It is shown that the quartet state contributes for temperatures higher than 700K. The computed rate coefficient can be described by a modified Arrhenius equation [[Formula: see text]] with [Formula: see text], [Formula: see text] and [Formula: see text] K.
Subject(s)
PhosphorusABSTRACT
The potential of doped aluminium clusters as catalysts for the water splitting reaction has attracted considerable scientific effort, however, the water-cluster interactions, which are a key step in the overall mechanism, are not fully understood. Here, we report an ab initio investigation of water adsorption on AlSi clusters at the MP2 level to elucidate the bonding and structural properties employing unary and binary 8- and 13-atom clusters, namely, Si8, Al2Si6, Al4Si4, Al8, Si13, Al2Si11, Al12Si, and Al13, which were selected by their relevance and energetic stability. We found that H2O binds via the O atom near to the on-top sites of the Si or Al atoms; in particular, there is a strong preference for the Al sites on the binary AlSi clusters, which is supported by the strong adsorption energy. Furthermore, we found a large enhancement of the adsorption energy on the Al2Si6 and Al2Si11 clusters, which can be explained by the cationic character of the Al site, which increases the Coulomb contribution to the Al+-O- interaction.
ABSTRACT
The geometry and stability of aluminum-silicon alloys up to 13 atoms are investigated using electronic structure methods. The results agree well with available experimental data, while also predicting new potential candidates for detection. The exploration of the potential energy hypersurface of such particles is performed using both a thorough assessment of permutational isomers from selected structures and also using an unbiased genetic algorithm. It is shown that both approaches attain similar results for the specific cases analysed here. Several structures with non-magic number of electrons are shown to be very stable, such as Al4Si4, Al2Si6, Al2Si8, Al8Si4 and Al2Si11. A molecular orbitals analysis based in the spherical jellium model and deviations from it is performed for a better understanding of the properties of selected clusters.
