where Using these three procedures, we have calculated the vibrational shifts of rotational constants B e,α -⟨B α ⟩, which were compared with those from the standard VPT2 computations. Since the shifts are sensitive to the absolute values of rotational constants, in statistical assessments (Table , Figure ) we used normalized quantities (B e,α -⟨B⟩)/B e,α = 1 -⟨B⟩/B e,α . In general, results from all tested combinations of methods for trajectory simulations (WS+MD, SWS+MD) and for calculation of rotational constants (MRC, MIITU, MIITO) correlated reasonably with reference VPT2 values. The MIITU and MIITO routines are the most physically justified, since the vibrationallyaveraged rotational parameter appears from the averaging of the rotational Hamiltonian as Ĥrot = ⟨0| 1 2