Spectroscopy of the Hydroxyl Ion OH + and Line Selection for Laser Induced Fluorescence IVDF Measurements

We present a modeling study on absorption and emission spectroscopy of the X3Σ− → A3Π rovibronic band of OH+ with application to the design of a laser-induced fluorescence (LIF) diagnostic for IVDF measurements in electric propulsion systems. The selection of absorption and emission transitions for the LIF scheme is discussed, with consideration of both spectroscopic and experimental parameters. The initial level populations and absorption cross sections are compared for the strongest absorption lines expected for rovibrational temperatures of 300 K, 1000 K, and 3000 K, along with the branching ratios and differences in energy between absorption and emission for all possible emission pathways following absorption on one of the strong absorption lines. The expected detection rate is calculated, and we compare the emission wavelengths of the LIF schemes with the emission spectra of other atoms and small molecules that may be present in complex molecular plasmas containing OH+.