Size-resolved studies of the structure and dynamics of neutral clusters using sodium doping and IR excitation modulated photoionisation spectroscopy.

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Size selective infrared spectroscopy of neutral clusters has previously been only of limited potential for larger clusters. In the first funding period we have developed further and characterized an approach based on sodium doping and two colour photoionisation, which now allows measuring infrared spectra of water clusters containing up to 1000 molecules with precise size selection. This method made it possible for the first time to follow the transition between amorphous and crystalline ice as a function of cluster size. This structure change could be traced by the shift of absorption maximum in the OH stretch region with increasing cluster size. In the second funding period the method shall be applied to characterize cluster structures, crystallization processes, phase transitions, and the interaction of sodium atoms with clusters. The research will focus on water because of the universal nature of this solvent molecule and the effective applicability of the method.