Diode-laser absorption spectroscopy of supersonic carbon cluster beams: The v₃ spectrum of C₅

A new spectroscopic experiment has been developed in which rovibrational transitions of supersonically cooled carbon clusters, which were produced by laser vaporization of graphite, have been measured by direct-absorption diode-laser spectroscopy. Thirty-six sequential rovibrational lines of the v₃ band of the C₅ carbon cluster have been measured with Doppler-limited resolution. The absorption spectrum is characteristic of a linear molecule with a center of symmetry. Least-squares analysis of the spectrum indicates an effective carbon-carbon bond length of 1.283 angstroms, in good agreement with ab initio quantum chemical calculations. This work confirms the detection of C₅ in IRC+10216 reported in the accompanying paper.