Crystalline germanium was ablated with light at 532 nm from a frequency-doubled Nd:YAG laser, and the resultant plume reacted with N-2 before deposition onto a substrate at 20 K. Multiple absorption lines at 891.8, 890.8, 890.4, 889.9, 889.4, 888.9, 888.4, 887.9, 887.5, and 887.0 cm(-1) that become enhanced after annealing of the matrix at 31 K are attributed to a species containing two Ge atoms in their isotopic variants: Ge-70, Ge-72, Ge-73, Ge-74, and Ge-76. Replacing N-14(2) with a mixture of N-14(2) and N-15(2) yields an additional multiplet in the region 867.1-862.1 cm(-1), whereas reaction of the same mixture subjected to microwave discharge yields a further multiplet in the region 878.9-874.0 cm(-1). The isotopic pattern indicates that the vibrational mode is associated with a Ge-N stretching motion that involves two equivalent Ge atoms and two equivalent N atoms. Theoretical calculations with density-functional theories (B3LYP/6-311+G* and B3LYP/aug-cc-pVTZ) predict nine stable isomers of Ge2N2, with linear GeNNGe and asymmetric angular Ge(GeNN) having the least energies. Among calculated vibrational wave numbers, IR intensities, and isotopic shifts for all isomers of Ge2N2, only those predicted for the asymmetric Ge-N stretching mode of linear GeNNGe fit satisfactorily with experimental results. GeNNGe is likely formed from direct reaction of Ge-2 and N-2 rather than from two-step reactions involving GeNN or GeN. (C) 2003 American Institute of Physics.