The formalism of the derivation of the kinetic energy operator (KEO) Eq. ( ) is well known . The first numerical implementation of the KEO operator dates back to the work of Laane et al. . Later, other groups proposed numerical approaches to determine the kinetic energy operator in the context of quantum dynamics . M. Ndong and coworkers developed the Fortran program TANA which provides an automatic computation of the kinetic energy operator in analytical form for polyspherical coordinates for any number of atoms. In this approach, the expression of the metric tensor is obtained analytically and it can be used in Eq. ( ) or in Eq. ( ). Furthermore, these expressions can be exported in several formats (MCTDH, MidasCpp, Fortran). The 3D-vibrational motion of the chloronium ion can be described in terms of the three valence coordinates q = {q 1 , q 2 , q 3 } ≡ {R 1 , R 2 , θ}, where R 1 and R 2 are the distances between the chlorine atom and the two hydrogen atoms and θ is the angle between the two Cl -H bonds. The application of the general KEO formula Eqs. with the Wilson normalization convention, ρ(q) = 1, (dν 1 = dR 1 • dR 2 • dθ) yields the following KEOs of the H 2 Cl + and its isotopologues: