A statistical theory used to describe unimolecular reactions. The RRK theory, put forward by Oscar Rice and Herman Ramsperger in 1927, and independently by Louis Kassel in 1928, assumes that a molecule is a system of loosely coupled oscillators. Regarding the coupling of the oscillators as loose enables calculations to be made on the statistical distribution of energy freely flowing between the vibrational modes. In RRK theory the rate constant for the decomposition of a molecule increases with the energy of the molecule. The RRK theory has been applied with success to some chemical reactions but is limited in its predictive power. The unsatisfactory features of the RRK theory are improved by the RRKM theory (Rice–Ramsperger–Kassel–Marcus theory).