Thesis of Sylvain Badin

Defense of thesis Sylvain Badin - laboratory PhLAM

Abstract :

Spacecraft electric propulsion provides a low thrust for a long period of time, which is particularly useful for interplanetary missions or for trajectory correction maneuvers for satellites. Recently, a new type of electric thruster was developed using iodine as a propellant. An iodine plasma is formed and an electric field expels the ions from the reactor, thus creating a thrust. The iodine has the advantage over other types of propellant (like Xenon) of being easy to store in a solid form and to be cheaper.
The improvement of iodine propulsion is hampered by the lack of knowledge about the chemistry of iodine plasma. In this work, the aim is to calculate the cross sections of some of the chemical reactions taking place in iodine plasma for use in kinetic models describing these plasmas. The mutual neutralization reactions between I+ and I− on the one hand, and I+2 and I− on the other, were studied. To do this, the potential energy curves of the systems I2 , I+2 and I2− were calculated using a relativistic quantum chemical method (four-component MRCI) and the three-dimensional fundamental potential energy surface of I3 was computed using a quantum chemical method including scalar relativity and spin-orbit coupling (CASSCF/PT2/SI). The cross sections of the reaction I+ + I− → I + I were then obtained using a semi-classical dynamics method: the Landau Zener Surface Hopping method, and were compared with experimental measurements carried out at the DESIREE double ion ring in Stockholm.
Further experiments at DESIREE showed that the mutual neutralization reaction between I2+ and I− formed three iodine atoms in their ground state and in a linear geometry, while the formation of I2 + I was not observed. A classical dynamics model was constructed based on the fundamental potential energy surface of I3 and was used to estimate the order of magnitude of the effective cross sections of this reaction. However, this model does not predict the distribution of products between I2 + I and I + I + I.
In addition, the absorption spectra of I2 and its ions I+2 and I2− were computed between 350 and 900 nm from their potential energy curves.

Keywords : ion-ion collisions,physical chemistry,plasmas,theoretical chemistry,electric propulsion,chemical kinetics