Ring-puckering combination band spectra of an isotopic impurity: 1,3-Disilacyclobutane-1,1,3-d₃

An isotope doping procedure has been used to produce a mixture containing 1,3-disilacyclobutane-1,1,3,3-d₄ (predominantly) and 29% of the -1,1,3-d₃ species. Investigation of the SiH stretching band at 2153 cm⁻¹ of the d₃ molecule shows fourteen sum and difference bands arising from the low-frequency ring-puckering motion. The analysis of this spectrum together with those for the d₀ and the -1,1,3,3-d₄ molecules demonstrate that a uniform amount of SiH₂ rocking is coupled to the ring-puckering motion in all isotopic species and that the kinetic energy model previously proposed is valid. The technique for analyzing isotopic impurities demonstrated in this work should be valuable for future investigations.