From Pathfinder Core Rulebook, which isn't enabled.

Acid Arrow

SPELL 2

Traditions arcane, primal

Cast

Range 120 feet

Targets 1 creature

You conjure an arrow of acid that keeps corroding the target after it hits. Make a spell attack against the target. On a hit, you deal 3d8 acid damage plus (rank ÷ 2, rounded down)d6 persistent acid damage. On a critical hit, double the initial damage, but not the persistent damage.

Heightened (+2) The initial damage increases by 2d8, and the persistent acid damage increases by 1d6.

Pathfinder Core RulebookOGL