The insertion of Hg into H-2 in a nitrogen matrix at low temperature has been induced using KrF laser irradiation, and the HgH2 produced is identified by FTIR absorption spectroscopy. This reaction is in competition with the E-V transfer from Hg(P-3(1)) to nitrogen, which has also been observed through the IR emission of vibrationally excited nitrogen. The spectra of isolated and complexed HgH2 have been observed. In the nitrogen matrix, annealing induces a much larger than usual frequency shift, which is related to the appearance of a vacancy close to the HgH2 at its formation. The photochemistry of the HgH2 .. Hg complexes at 249 nm gives a new molecule HHgHgH, which may be dissociated. The isolated HgH2 is shown to be very stable under 249 nm irradiation and is found to dissociate under 193 nm irradiation. All the absorption studies have also been done with deuterated compounds, and the force constants of the HgH bonds of the new molecules have been determined.