Irradiation of a sample near 3.0K of ethyne, C 2 H 2 , in a Ne matrix with vacuum ultraviolet radiation from a synchrotron produced various photoproducts that were analyzed through their infrared absorption spectra. Photolysis with light at 171nm yielded as major product ethynyl radical, C 2 H. Based on observed D-isotopic shifts and comparison of observed vibrational wavenumbers and isotopic ratios with values predicted with quantum-chemical calculations, we identified the ν 1 and ν 3 modes of C 2 H to be 3293.3 and 1835.7cm −1 , respectively. The fundamental C–H stretching ν 1 mode of C 2 H was determined for the first time in solid Ne.