Many-photon excitation of spherically symmetric molecules in an infrared laser field by weakly forbidden $\triangle R\ne0$, $\triangle n\ne0$ vibrational–rotational transitions

An analysis is made of a model of multistage excitation of triply degenerate vibrations of spherically symmetric molecules in a strong infrared laser field. This involves allowing for weakly forbidden $\triangle R\ne0$, $\triangle n\ne0$ transitions. It is shown that as a result of these transitions, a system of up to several dozen multistage resonances is established within the absorption band. These resonances cover a group of rotational levels with different values of $J$ (up to 110–20 values) and ensure that a considerable proportion of the molecules is excited to high vibrational states (up to $\upsilon=10-15$).