In the present work the first spectroscopic data concerning solid butadiene are presented. FTIR and Raman spectra of solid trans-1,3 butadiene in the ordered phase I were recorded at atmospheric pressure down to 12 K. The FTIR technique was used to characterize the phase diagram of butadiene in the 0-7 GPa and 150-300 K pressure-temperature range. Besides phase I another solid phase (phase II), orientationally disordered, was found to be stable at pressures above 0.5 GPa between the liquid and the ordered phase I. A monoclinic C-2h(5) crystal structure with two molecules per cell sitting on C-i sites is proposed for phase I. (C) 2002 Elsevier Science B.V. All rights reserved.