One then integrates over all energies to get the total reaction rate, using the Maxwell–Boltzmann distribution and the relation: r V = n A n B ∫ ∫ 0 ∞ ∞ S ( E ) E e − − E G E 2 E π π ( k T ) 3 e − − E k T 2 E m R d E where m R = m 1 m 2 m 1 + m 2 is the reduced mass.