The lowest frequency vibrational fundamental of disilane: A three-band analysis

The lowest frequency perpendicular fundamental band ν9 of disilane has been analyzed to investigate torsion mediated vibrational interactions. We report here a three-band analysis involving torsional levels built on the ground state, the ν9 vibrational fundamental, and ν3 fundamental. This analysis includes transitions from the far-infrared torsional bands, ν4, 2ν4 − ν4, 3ν4 − 2ν4, two perturbation-allowed rotational series from the overtone band 3ν4 and transitions restricted to −21 ⩽ kΔk ⩽ 21 in the ν9 fundamental band. An excellent fit to the included data was obtained. Two interactions are identified in this fit, a resonant Coriolis interaction between the ν9 torsional stack and that of the ground vibrational state and a Fermi interaction between the ν3 fundamental and the gs. The introduction of the Fermi interaction causes a large change in the barrier height for the ground vibrational state and makes the barrier shape parameter redundant, indicating that the vibrational contributions to the experimental barrier shape are dominant. Such effects have also been observed for ethane and other similar molecules.