Cryokinetics and spin quenching in the N2 adsorption onto rhodium cluster cations

The kinetics of N-2 adsorption onto gas phase Rh-i(+) clusters (i = 5-15) within 26 K He buffer gas have been investigated by Fourier Transform Ion Cyclotron Resonance (FT-ICR) mass spectrometry, with particular focus to clusters i = 5,6,7,9. The adsorption limits m = m(max) of [Rh-i(N-2)(m)](+) clusters strongly depend on the size of the clusters. Some Rh-i(+) clusters reveal an intermittent adsorption limit m(x), which implies a rough cluster surface. Most of the clusters reveal smooth surfaces, which consist of Rh atoms with similar next neighbour coordination. The kinetic fits and relative rate constants reveal the sequential adsorption of N-2 as the only significant reaction channel. In some cases, we find N-2 desorption steps at high N-2 loads indicating adsorption-desorption equilibria. For these steps, we determined Gibbs energies from the relative rate constants. We observed a significant reluctance towards N-2 adsorption for the Rh-5(+) cluster, indicated by significant desorption at low N-2 coverage. Our DFT calculations model the energetics of the N-2 adsorption onto Rh-5(+) in terms of coverage dependent 'spin valley' curves, and we conclude that an adsorption induced spin quenching takes place upon considerable N-2 coverage, m > 4.

Automated summary

The study reveals that the adsorption limits of N-2 on Rh-i(+) clusters strongly depend on the cluster size, with some clusters having rough surfaces and others having smooth surfaces. The sequential adsorption of N-2 is found to be the only significant reaction channel, with occasional desorption steps indicating adsorption-desorption equilibria. DFT calculations show that an adsorption induced spin quenching occurs at considerable N-2 coverage on Rh-5(+).