The infrared spectra of acetylene monomer and solid generated in a pulsed supersonic jet have been obtained near 3300 cm(-1) using step-scan Fourier transform infrared (FTIR) absorption spectroscopy. The rotational temperature of monomer was determined to be as low as 10 K. A broad band was also observed between 3220 and 3260 cm(-1) with a dominant peak at 3234 cm(-1), which was assigned to the high-temperature cubic phase of solid acetylene. (C) 2002 Published by Elsevier Science B.V.