Morphed intermolecular potential of OC:HCCH complex based on infrared quantum cascade laser spectroscopy

► Quantum cascade laser spectroscopy of OC-HCCH complex. ► The ground state low frequency bend is determined to be at 20.48361(20) cm−1. ► The morphed potential has two identical linear global minima OC-HCCH. ► For OC-HCCH Re = 5.018(2) Å and De = 360(4) cm−1. ► The isomerization energy OC-HCCH/CO-HCCH is predicted to be 86(10) cm−1.