Irradiations at lambda > 180 nm and > 230 nm of CH3COCN (CD3COCN) trapped in an argon matrix at 10 K have been performed and monitored by Fourier transform infrared spectroscopy. For both wavelengths, the first photoreaction product is acetyl isocyanide. At lambda > 180 nm acetonitrile and methyl isocyanide are obtained as final products. They are formed by photolysis of acetyl isocyanide and acetyl cyanide, respectively. Unstable intermediates, such as ketene:HCN and ketene:HNC complexes, H2CNCH zwitterion, and H2C2NH keteneimine, not observed in the gas phase, are trapped and identified at our experimental temperature. The complexes have an L-shaped structure with a hydrogen bond between the oxygen atom of ketene and the hydrogen atom of HCN or HNC. A pathway process is proposed and compared with the ones determined in the ground state by ab initio calculations.