Phosphorus cluster anions are investigated with CID MS.

The CID MS results of ${\text{P}}_{2m+1}^{-}$ are very different with those of ${\text{P}}_{2m+1}^{+}$.

For ${\text{P}}_{2m+1}^{-}$ (3 ≤ m ≤ 11), their dissociation channels are characterized by the loss of a P₂ unit.