Jacobi 3-body reduced mass: μ_{12,3} = (m1+m2)·m3/(m1+m2+m3)

Jacobi coordinates decompose an n-body center-of-mass-frame into (n-1) independent coordinates. For three particles: ρ = r_2 - r_1 (first-pair separation) and λ = r_3 - (m_1·r_1 + m_2·r_2)/(m_1+m_2) (third-particle to first-pair…