Abstract The polarized infrared spectrum of a highly-oriented crystal of TCNE have been measured, tegether with the Raman spectrum of a sample consisting of several lumps of the crystals. The infrared spectra of the powedered solid, solution, and vapor have also been observed for comparison. Under the assumption of the Vh symmetry, the normal vibrations of TCNE have been calculated for the in-plane modes by the use of the GF matrix method. The basic UBFF, as well as the modified one containing cross terms between the C=C and C–C bonds, has been used as the potential function for this molecule. The frequencies calculated with the modified UBFF agree well with the observed values. The potential energy distributions have also been calculated, and the nature of the in-plane fundamental vibrations has been elucidated. The tentative assignments have been made to the out-of-plane fundamental vibrations and to the overtone and combination vibrations.