Exploding two gameobjects from the center of an collision

I have two GameObjects that collides and when they do that I want to add an explosionforce at the position (center?) of the collision to make them "explode" away from each other. Is this data stored in the Collision or is there an easy way of calculating it?

float explosionForce = 300.0f; float explosionRadius = 6.0f; float explosionUpwardsModifier = 0.0f; Vector3 explosionPosition = ?;

rigidbody.AddExplosionForce(explosionForce, explosionPosition, explosionRadius, explosionUpwardsModifier);