Knowledge Bank

The far-infrared spectra of several deuterated analogues of trimethylene sulfide $(\alpha -d2,\beta -d2,\alpha ,\alpha \prime -d4$ and $d_{6}) $ have been measured in the vapor phase, all showing the usual sequence of Q-branches arising from transitions between ring puckering energy states. The isotopic dependence of the double minimum potential function governing the out-of-plane motion will be discussed briefly. Several combination band progressions resulting from ring puckering-vibrational interactions, notably in the $CH2$ scissoring region, are reported. It is found that for some vibrationally excited states the puckering potential function does change appreciably from its form in the ground state.