On the use of Computational Chemistry to understand the Generation processes Julien Lam1, Abdul-Rahman Allouche1, Christophe Dujardin1, Gilles Ledoux1, David Amans1 1. Université Lyon 1, F-69622 Villeurbanne, France, UMR5306 CNRS, Institut Lumière Matière, PRES-Université de Lyon, F-69361 Lyon, France E-mail: [email protected]

In the context of Pulse Laser Ablation in Liquid (PLAL), it appears crucial to obtain the most complete understanding of the highly complex growth processes. Various tools have already been developed in this framework. Among them, we can cite plasma spectroscopy, dynamic light scattering and shadowgraph imaging. In any cases, these tools do not provide any information about the chemical composition of the gas phase system. Indeed, we are still lacking of information concerning what can happen after the plasma extinction when the ablated materials is confined in a gas bubble. It seems reasonable to consider such a system as a catalyser for gas phase reactions. As a consequence, we worked on the ablation of an Al2O3 target by a Nd:YAG laser (f=10Hz, t=10ns, =355nm). Using plasma spectroscopy, we showed previously[1] that Aluminium monoxide molecules (AlO) are continuously generated inside the plasma. Therefore, at the plasma quenching, we observe a system mainly composed of AlO diatomic species. Furthermore, we developed different instruments used in computational chemistry to fill-in the blank left in this investigation. Density Functional Theory (DFT) calculationsx enabled to simulate the physical properties of the (AlO) n structures with N going from 2 to 8. These outcomes are first blocks towards the predication of spectroscopy signature from molecules bigger than the usual diatomic ones. Also, we used these ab initio results as inputs to build a semiempirical interaction potential between aluminium and oxygen atoms. Such a model should provide a numerical instrument to predict the chemical reactions but also to find the most stable structures for nanoparticles where N is couple orders of magnitude bigger. N=8

1.857 Å

Figure 1 Typical geometry obtained using DFT calculation for (AlO)8

References [1] J. Lam, D. Amans, F. Chaput, M. Diouf, G. Ledoux, N. Mary, K. Masenelli-Varlot, V. Motto-Ros, C. Dujardin,-al2o3 nanoparticles synthesized by pulsed laser ablation in liquids: A plasma analysis, Phys. Chem. Chem. Phys., 2014,16, 963-973