Strain dependence of the vibrational modes of a diacetylene crystal

Resonance Raman spectroscopy has been used to measure the strain dependence of four high‐frequency vibrational modes in a single crystal of toluene sulfonate diacetylene polymer. The 0.62‐μm thick crystal was stretched elastically to 4% strain before fracture occurred. This was equivalent to an ultimate tensile strength of 2.0 × 109 N m−2. The strain dependence of the vibrational modes has been interpreted using a simple point mass and anharmonic spring constant model. A Fermi resonance was observed for two vibrational modes which are degenerate at 2.1% strain and a 1464 cm−1 frequency.