Imbuement (3.5e Feat)
From D&D Wiki
There comes a time in every spell caster's life when they wanna to pick someone off that's out of reach or smack someone with a sword that explodes in their face.
Prerequisite: Int, Cha or Wis 15, Spellcraft 4 Ranks, Weapon Focus
Benefit: You can imbue a spell into the weapon with which you have Weapon Focus. or in the case of ranged weapons, imbue your spells to the ammo used. A weapon Imbued with a spell casts it immediately on hitting a target (whether it was the intended target or not). Only one ammo can be imbued at a time (for example, one arrow). An Imbued spell uses up a spell slot one level higher than the spell's normal level when applied to a melee weapon or two levels higher when applied to ammo for a ranged weapon.