A light-induced transient bis(2,4,6-trichlorophenyl)carbene trapped in a yield of ca, 20% in the crystal of the precursor diazomethane was characterized by X-ray crystallography at low temperatures. The most interesting geometrical parameters are the carbenic angle a and the bond distances between the carbenic carbon and the phenyl carbons. The obtained theta is 142(2)degrees, while the distances are 1.437(15) and 1.423(16) Angstrom, respectively. These values are significantly different from the corresponding values for the precursor diazomethane (127.1(1)degrees and 1.477(1) and 1.480(1) Angstrom, respectively). On the basis of IR spectroscopy and theoretical calculations, the carbene is judged to be in the triplet ground state.