The hydrogenation of silicon material proves great advantages concerning its photovoltaic properties and secure a key for the elimination of crystalline defects during the basaltic growth of the crystal. In our process, silicon particles are hydrogenated in the thermal plasma torch at atmospheric pressure. So, the aim of this work is to characterise the physical properties of the plasma flow in order to understand the interaction appearing between particles and hydrogenated plasma flow during the treatment. Highly excited states of atomic hydrogen, responsible of the silicon hydrogenation, have been detected in the plasma. These atomic hydrogen lines have been used to determine the electronic density on the plasma axis. Electronic temperature of different plasma mixture have been obtained by the Boltzmann plot method.