Microwave and vibrational spectra, ab initio calculations, conformational stabilities and assignments of the fundamentals of the Cₛ conformer of n-butylsilane

The vibrational spectrum of n-butylsilane is described. Complete assignments of fundamentals are made for the anti–anti (aa) conformer of Cₛ symmetry. The relative stabilities of the five different conformers are calculated, and the (aa) conformer emerges as the conformer of lowest relative energy, and thus the most abundant, entirely dominating the infrared and Raman spectra as confirmed by the spectra of the annealed crystal. The dipole moments of all the conformers are calculated to lie between 0.88 and 1 Debye, similar to the dipole moments of the conformers of n-butylgermane. Microwave measurements of this molecule seeded in a molecular jet were made using Fourier-transform microwave spectroscopy and confirmed the presence of the aa conformer, in addition to the anti–gauche (ag) and gauche–anti (ag) conformers. Measurement of rotational spectra for all four ¹³C-substituted isotopologues as well as the ²⁹Si and ³⁰Si species for the aa conformer allowed a heavy atom structure determination for this conformer.