Competitive molecular and dissociative hydrogen chemisorption on size selected doubly rhodium doped aluminum clusters

The interaction of hydrogen with Al_nRh_2^+ (n = 10–13) clusters is studied by mass spectrometry and infrared multiple photon dissociation (IRMPD) spectroscopy. Comparing the IRMPD spectra with predictions obtained using density functional theory calculations allows for the identification of the hydrogen binding geometry. For n = 10 and 11, a single H_2 molecule binds dissociatively, whereas for n = 12 and 13, it adsorbs molecularly. Upon adsorption of a second H_2 to Al_{12}Rh_2^+, both hydrogen molecules dissociate. Theoretical calculations suggest that the molecular adsorption for n = 12 and 13 is not due to kinetic impediment of the hydrogenation reaction by an activation barrier, but due to a higher binding energy of the molecularly adsorbed hydrogen–cluster complex. Inspection of the highest occupied molecular orbitals shows that the hydrogen molecule initially forms a strongly bound Kubas complex with the Al_{11–13}Rh_2^+ clusters, whereas it only binds weakly with Al_{10}Rh_2^+.

Publication year:2018

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Authors:International

Authors from:Higher Education

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