Reaction Rate Coefficient
Reaction rate coefficients are the phenomenological coefficients occurring in rate expressions for elementary chemical reactions. They can be determined either experimentally or theoretically. Bimolecular rate coefficients are expressed in units of cm3 s−1 and unimolecular ones in units of mol. s−1. Typical values for interstellar chemistry are 10−9 cm3 s−1 for ion-neutral reactions and 10−11 cm3 s−1 for neutral-neutral reactions.