The infrared spectra (3500-50 cm Γ1 ) of the gas and solid and the Raman spectrum (3200-30 cm Γ1 ) of liquid germacyclopentane, c-C 4 H 8 GeH 2 , have been recorded. Additionally, the infrared spectra (3200-400 cm Γ1 ) of liquid xenon solutions have been recorded at Γ65 and Γ95 Β°C. In all of the physical states only the twisted C 2 conformer was detected. The conformational energetics have been calculated with the MΓΈller-Plesset perturbation method to the second order, (MP2(full)) as well as with density functional theory by the B3LYP method utilizing a variety of basis sets up to 6-311G(2d,2p). All of these calculations predict only the twisted conformer as the stable form with an average barrier to planarity of 2756 cm Γ1 (32.97 kJ/mol) from the MP2 calculations and a significantly lower value of 2128 cm Γ1 (25.45 kJ/mol) from the DFT calculations with neither calculations being significantly effect by inclusion of diffuse functions. The C s conformer (envelope) has a lower energy of 700 cm Γ1 (MP2) and 400 cm Γ1 (B3LYP) than the planar form. Thus, the path between the two identical C 2 conformers is by a pseudorotational motion rather than through the planar form. From the isolated GeH frequency from the GeHD isotopomer the GeH distance was calculated to be 1.532(2) A Λ. By utilizing the previously reported microwave rotational constants for four isotopomers ( 70 Ge, 72 Ge, 73 Ge, 74 Ge) combined with the structural parameters predicted from the MP2(full)/6-311+G(d,p) calculations, adjusted r 0 structural parameters were obtained. The determined heavy atom distances are: r 0 (GeC) = 1.972(5); r 0 (C 2 C 4 ) and (C 3 C 5 ) = 1.541(5); and r 0 (C 4 C 5 ) = 1.533(5) A Λand the angles in degrees: \CGeC = 93.6(5)Β°; \GeCC = 102.6(5)Β°; \CCC = 109.4(5)Β°with the two dihedral angles \GeCCC = Γ38.4(3)Β°and \CCCC = 53.7(3)Β°. A complete vibrational assignment is given for the twisted (C 2 ) conformer for the normal species and the GeD 2 isotopomer which are supported by normal coordinate calculations with scaled force constants from MP2(full)/6-31G(d) calculations. The results of these spectroscopic and theoretical studies are discussed and compared to the corresponding results for some similar molecules.