| Résumé | Crystalline germanium was ablated with light at 532 nm from a frequency-doubled Nd:YAG laser, and the resultant plume reacted with N₂ 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: ⁷°Ge, ⁷²Ge, ⁷³Ge, ⁷⁴Ge, and ⁷⁶Ge. Replacing ¹⁴N₂ with a mixture of ¹⁴N₂ and 15N₂ 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 Ge₂ and N₂ rather than from two-step reactions involving GeNN or GeN. |
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