Recent work has shown that the negative bias temperature instability (NBTI) can be significantly suppressed through the incorporation of fluorine in the gate oxide of pure SiO2 pMOSFETs. In this study, we use spin dependent recombination and standard gated diode current measurements to investigate the atomic-scale processes involved in fluorine's suppression of NBTI. We find that fluorine can effectively passivate Si/SiO2 P b0 center defect precursors, but is much less effective at passivating Si/SiO2 Pb1 center defect precursors. Since these two defects have significantly different densities of states, our results may be useful in modeling NBTI response in fluorinated oxide devices. Our results also provide a fundamental explanation for the observation that fluorination has a strong effect on NBTI in "pure" SiO2 MOS devices, but is ineffective at reducing NBTI in nitrided oxide devices.