Infrared spectra of the weakly-bound C 2H 2-CO 2 and C 2H 2-N 2O complexes in the region of the 2CH acetylene overtone band (∼1.52μm) were recorded using CW-cavity ring down spectroscopy in a continuous supersonic expansion. A new, c-type combination band is observed in each case. The rotational analysis of low J, K lines is performed and rotational constants are obtained. The band origins are 40.491(2) and 40.778(2) cm -1 higher in energy than the 2CH excitation bands for C 2H 2-CO 2 and C 2H 2-N 2O, respectively. The combination band is assigned in each case as involving intermolecular torsional excitation combined to 2CH. The values of the torsional vibrational frequency and of the x CH/torsion anharmonicity constant are briefly discussed. Copyright © 2011 Taylor and Francis Group, LLC.