The SNO(-) and OSN(-) anions are shown in this work to be very stable negatively charged species in line with other recent work [T. Trabelsi et al., J. Chem. Phys. 143, 164301 (2015)]. Utilizing established quartic force field techniques, the structural and rovibrational data for these anions are produced. The SNO(-) anion is less linear and has weaker bonds than the corresponding neutral radical giving much smaller rotational constants. OSN(-) is largely unchanged in these regards with inclusion of the additional electron. The S-N bond is actually stronger, and the rotational constants of OSN(-) versus OSN are similar. The vibrational frequencies of SNO(-) are red-shifted from the radical while those in OSN(-) are mixed. OSN(-) has mixing of the stretching modes while the S-N and N-S stretches of SNO(-) are largely independent of one another. The ω3 stretches are much brighter in these anions than they are in the radicals, but the ω1 stretches are still the brightest.