Signals of Free Polarization Decay in Gas $^{13}$CH$_3$F.

Signals of free polarization decay on a background of transient nutations generated by the method of levels Stark switching in $^{13}$CH$_3$F gas are investigated. Polarization of 9P(32) CO$_2$-laser radiation is parallel to a Stark field. Equidistant spectrum arises because of the linear Stark effect on 0–1 $\nu_3$ R(4,3) $^{13}$CH$_3$F transition, and the beats of free polarization decay signals corresponding to the transitions with different magnetic numbers ($M=-4,\dots,0,\dots,4$) are observed. These signals look like peaks with a period inversely proportional to the intensity of a Stark field. From this dependence the estimate is made for the weighed difference of $^{13}$CH$_3$F permanent dipole moments in the ground and vibrational excited states.