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 ( rz) 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 rz(CC) bond length is determined to be 1.5351(2) Å, which is significantly longer than previous estimates involving electron diffraction data.