Infrared spectroscopic studies of partially deuterated ethanes and the r0, rz, and re structures

Samples of CH ₃CH ₂D, CH ₃CHD ₂, CD ₃CH ₂D, and CD ₃CHD ₂ have been prepared, and their infrared spectra recorded. Analysis of type B or type C "perpendicular" bands has enabled the rotational parameter ( A ₀ - overlineB₀) to be determined for all four species. These have been combined with existing infrared, Raman, and microwave data for CH ₃CH ₃, CD ₃CD ₃, and CH ₃CD ₃ species, to determine the ground state ( r₀) and ground state average ( r_z) structures within narrow limits. Zero point energy effects on the average structure are determined to be a CH bond shortening of 0.0015(3) Å and an HCC angle opening of 0.010(5)° on deuteration. These effects enable the equilibrium structure of ethane to be estimated. The r_z(CC) bond length is determined to be 1.5351(2) Å, which is significantly longer than previous estimates involving electron diffraction data.