Experimental study of gas phase titanium and aluminum oxide clusters

We present an experimental study of the vibrational properties of gas phase titanium oxide and aluminum oxide clusters. The titanium and aluminum oxide clusters have a stoichiometry of (Ti2O3)x–(TiO2)y (with (x, y) from (2, 4) to (11, 29)) and AlO–(Al2O3)n (5 ≤ n ≤ 70). The vibrational properties of the clusters are obtained using infrared resonance enhanced multi-photon ionization (IR-REMPI) spectroscopy. Titanium oxide clusters have a strong vibrational band at ~13.5 μm, suggesting that their structure is close to the rutile bulk phase of TiO2. Aluminum oxide clusters seem to have a structure comparable to the bulk γ-Al2O3; their IR-REMPI spectra exhibit a vibrational band at ~11 μm and another band at ~15 μm which appears in the spectra of clusters containing more than 7–8 Al atoms and becomes more intense as the cluster size increases. As hot neutral clusters are observed to evaporate more easily electrons than neutral fragments, one can conclude that they are very stable and thus very good nucleation seeds for dust growth.