Reactive neutral species densities for various conditions in dual frequency capacitively coupled discharges of Ar/O2, Ar/N2, and Ar/H2 were determined using optical emission spectroscopy, Kr actinometry, and modeling. The reactive neutral species probed in this work include O, O2, N, N2, H, and H2. Densities are reported as a function of pressure (5–60 mTorr), percent Ar in the feed gas (1%–86%), source power (50–800 W), and bias power (0 W, 200 W). It was found that increasing the pressure from 5 to 60 mTorr resulted in order of magnitude increases in atomic species densities for all ash chemistries. At 30 mTorr, percent dissociation is relatively low (≤15%) for all species. Also, at 30 mTorr, the addition of Ar resulted in a small decrease in N and H densities, but an order of magnitude increase in O density. Based on modeling, it is proposed that the increase in O density is due to an increasing contribution of Penning dissociation with increasing Ar density. Only the source power contributed significantly to O and N radical densities, but 200 W bias power generated a significant H radical density above that generated via the source power. Details of these results are discussed in comparison with theory and literature.