where ν is the photon frequency, and the D is the energy threshold for the observed reaction. This procedure allows to take into account processes occurring in the measurements and practically damps the low-frequency wide band below 1000 cm -1 , which is predicted by theory but could not be observed experimentally (see for a discussion). In our work we assumed D = 383 cm -1 , which corresponds to the Gibbs free energy of the probing reaction (Equation ). The comparison of experimental and all modeled in this work spectra is shown in Figure . Expectedly, VPT2 fails by producing a negative value for the lowest fundamental frequency, due to large-amplitude motions. MBS-AT+MD shows the fine band structure, whereas the WS-based methods demonstrate the broadening of the peaks without significant anharmonic shifts. For comparison, a path-integral MD simulation of CH + 5 did not show significant broadening. This may indicate a too aggressive sampling in WS and SWS for such a flexible molecule. Thus, the classical MD appears to be more effective for reproducing the vibrational band structure in this case.