Intermodulated Laser Induced Fluorescence Measurements of Singly Ionized Atomic Iodine

Electrostatic propulsion systems widely use xenon as a propellant, however, iodine is one candidate under consideration to replace xenon due to its attractive qualities as a propellant. A key tool missing in the development of iodine-fueled propulsion systems is a spatially resolved diagnostic technique to analyze ion flow rates and temperature of the thruster plasma, in order to characterize the performance of such systems without perturbing the plasma. Previous work investigated the lineshape of singly-ionized atomic iodine (I II) with laser nduced fluorescence (LIF), but could not resolve the hyperfine structure of the ⁵D⁰₄ and ⁵P₃ states [Steinberger and Scime, Journal of Propulsion and Power, 34, 2018]. Here, an  ntermodulated LIF technique is used to measure a Doppler-reduced lineshape of the same I II transition. A Monte Carlo fitting algorithm is used to fit the transition lineshape, where  the magnetic dipole and electric quadrupole coupling coefficients are left as free parameters with constraints from theory. We report most probable values of the hyperfine coupling coefficients for these I II states.