Development Challenges in Bhutan

Abstract

Fourier transform spectra of the four-membered heterocycle silacyclobutane (c-C3H8Si)(SCB) were recorded in the infrared region from 500 to 800 cm-1 with a resolution of 0.000959 cm-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 ∼543 cm-1 and the α-CH2 rocking mode (ν14) at ∼737 cm-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, 12 371 infrared transitions were assigned for the ring deformation and α-CH2 rocking bands and combined with those from analysis of the ring puckering (158 cm-1) and SiH2 rocking modes (410 cm-1) (Chen and van Wijngaarden, 2013). A 10 state fit was performed from the resulting data set containing 20 626 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.