Hydrogen chemisorption on singly vanadium-doped aluminum clusters

The effect of vanadium doping on the hydrogen adsorption capacity of aluminum clusters (Al_n^+, n=2-18) is studied experimentally by mass spectrometry and infrared multiple photon dissociation (IRMPD) spectroscopy. We find that vanadium doping enhances the reactivity of the clusters towards hydrogen, albeit in a size-dependent way. IRMPD spectra, which provide a fingerprint of the hydrogen binding geometry, show that H_2 dissociates upon adsorption. Density functional theory (DFT) calculations for the smaller Al_n^V+ (n=2-8,10) clusters are in good agreement with the observed reactivity pattern and underline the importance of activation barriers in the chemisorption process. Orbital analysis shows that the activation barriers are due to an unfavorable overlap between cluster and hydrogen orbitals.