Analysis of the rotation-vibration-inversion infrared spectrum of the ν10 and ν14 bands of silacyclobutane

Abstract

Fourier transform spectra of the four-membered heterocycle silacyclobutane (c-C3H8Si)(SCB) were recorded in the infrared region from 500 to 800cm−1 with a resolution of 0.000959cm−1 using synchrotron radiation from the Canadian Light Source. Two fundamental bands observed in this region have been rotationally analyzed. These correspond to motions best described as the in-plane ring deformation mode (ν10) at ∼543cm−1 and the α-CH2 rocking mode (ν14) at ∼737cm−1. Both bands exhibit complex, dense spectral patterns that arise from ring inversion tunnelling of the puckered SCB ring through a planar (C2v) intermediate configuration. Analysis of these patterns revealed rotation-vibration transitions between states of the same inversion symmetry for the ν10 mode as well as rotation-vibration-inversion transitions that connect states of different inversion symmetry. Only rotation-vibration-inversion transitions are observed in the ν14 band due to symmetry as the vibration (A2) is IR forbidden. In total, 12371 infrared transitions were assigned for the ring deformation and α-CH2 rocking bands and combined with those from analysis of the ring puckering (158cm−1) and SiH2 rocking modes (410cm−1) (Chen and van Wijngaarden, 2013). A 10 state fit was performed from the resulting data set containing 20626 rotation-vibration-inversion transitions and provided accurate band centres, ring inversion splittings, rotational and centrifugal distortion constants for the lowest energy states of the dynamic silacyclobutane ring.