/b N/-body quantum-mechanical Hamiltonians: extrapotential terms

After a brief review of the basic algebraic ingredients needed to express the quantum-mechanical Hamiltonian of an /b N/-body system in terms of curvilinear coordinates and quasi-momentum operators, the effect of changing the normalization convention is thoroughly investigated, with special emphasis on the occurrence of a nondifferential term in the expression of the kinetic energy operator, the so-called `extrapotential' term. Four examples are presented, concerning various parametrizations and various referentials, for acetylene-like molecules.