The rates for free ion production through electron transfer in collisions between K(np) Rydberg atoms and C2Cl4, CS2, and O-2 are measured as a function of Rydberg atom velocity for intermediate values of n, 13 less than or equal to n less than or equal to 21. The data show that postattachment interactions between the product positive and negative ions are important and can lead to conversion of internal energy from the negative ion, which is formed in an excited state, into translational energy of the product ion pair. This energy conversion occurs without ion-ion neutralization and can stabilize the negative ion against dissociation or autodetachment.