The infrared spectra (3500-50 cm - 1 ) of the gas and solid and the Raman spectra (3500-50 cm - 1 ) of the gas, liquid and solid have been recorded for 4-fluoro-2-pentyne, CH 3 C=CCHFCH 3 . Equilibrium geometries and energies have been determined by ab initio (HF and MP2) and hybrid density functional theory (DFT) by the method B3LYP calculations with a number of basis sets. A vibrational assignment is proposed based on the force constants, relative intensities, depolarization ratios from the ab initio and DFT calculations and rotational-vibrational band contours obtained by using the calculated equilibrium geometries. The methyl group attached to the C=C triple bond exhibits almost completely free rotation and this is accompanied by the observation of Coriolis sub-band structure on two of the near degenerate methyl vibrations. The Coriolis coupling constants have values of 0.181+/-0.033 and -0.137+/-0.078 for the stretch and deformation, respectively. Torsional transitions of the other methyl group are evident in the far infrared spectrum from which a barrier to internal rotation of 1465+/-30 cm - 1 is derived which agrees well with the theoretically predicted barrier value. The results are compared to the corresponding quantities of some similar molecules.