Sodium microsolvation in ethanol: common features of Na(HO-R)n (R=H, CH3, C2H5) clusters

Ethanol clusters are generated in a continuous He seeded supersonic expansion and doped with sodium atoms in a pick-up cell. By this method clusters of the type Na(C(2)H(5)OH)(n) are formed and characterized by determining size selectively their ionization potentials (IPs) for n = 2-40 in photoionization experiments. A continuous decrease to 3.1 eV is found from n = 2 to 6 and a constant value of 3.07 ± 0.06 eV for n = 10-40. This IP evolution is similar to the sodium-water and the sodium-methanol system. Quantum chemical calculations (B3LYP and MP2) of the IPs indicate adiabatic contributions to the photoionization process for the cluster sizes n = 4 and 5, which is similar to the sodium-methanol case. The results of the extrapolated IPs and the vertical binding energies (VEBs) of cluster anions are compared with the recently reported VEBs of solvated electrons in liquid water, methanol, and ethanol solutions in the range of 3.1-3.4 eV. The new results imply that the extrapolated VBEs of solvated electrons in anionic clusters match the VBE in liquid water, while they are about 0.5 eV too low for methanol. The influence of the presence of counterions on these findings is discussed.