## Dinitrogen Adsorption and Activation on Pure and Alloy Metal Cluster Cations Studied by Cryo Adsorption Kinetics and Infrared Spectroscopy

• The present thesis investigates the interaction of size selected transition metal cluster cations with $$N_2$$ adsorbate molecules under cryogenic conditions. A tandem cryo ion trap mass spectrometer facilitates the recording of the adsorption kinetics of gases onto size selected transition metals clusters under isothermal cryo conditions. The combination with a tunable OPO/OPA laser system allows for the recording of Infrared-(Multiple) Photodissociation (IR-(M)PD) spectra of the resulting cluster adsorbate complexes. The comparison of the experimental results with DFT modelling allows for structural assignments and the evaluation of the clusters’ electronic properties. We apply the combination of these methods on rhodium, rhodium-iron alloy and tantalum clusters and present the results in seven research studies. The IR-(M)PD spectra of rhodium cluster adsorbate complexes indicate co-existing isomers and a spin quench with increasing number of adsorbed $$N_2$$. Adsorption kinetics allowed to assign clusters with rough and smooth surfaces and to find features of adsorption reluctance. Calculated spin valley curves reveal a spin quench upon $$N_2$$ adsorption onto the $$Rh_5^+$$ cluster. Band shifts in the IR-(M)PD spectra of sequential $$N_2$$ adsorption onto the $$Rh_6^+$$ cluster are interpreted in terms of adsorbate induced charge dilution, which is supported by DFT calculations. Our combined approach reveals alloy like mixed rhodium iron clusters with adsorption site dependent $$N_2$$ stretching vibrations, where $$N_2$$ preferentially adsorbs onto rhodium sites. The $$Ta_4^+$$ cluster facilitates the cleavage of the initial two $$N_2$$ adsorbate molecules. By help of IR-(M)PD spectroscopy and DFT modelling we are able to assign a novel AEAS (across edge-above surface) mechanism and to assign an activated side-on intermediate of the third adsorbate molecule. The investigation sequential $$N_2$$ adsorption onto the $$Ta_5^+$$ cluster does not reveal any evidence for $$N_2$$ activation. DFT modelling reveals low spin states.