FTIR matrix isolation and ab initio investigations of the Si2N and BNSi molecules

The equilibrium vapors produced when silicon nitride is heated in a boron nitride (BN) Knudsen cell over a temperature range of 1500–2300 K were analyzed by FTIR matrix isolation technique. An absorption at 910 cm−1 is assigned as the antisymmetric stretching mode of the symmetric linear molecule SiNSi, in good agreement with ab initio calculations. A pair of doublets in the absorption spectrum at 1548.5/1544.6 cm−1 and 1528.0/1523.6 cm−1 are assigned to the 10B–N and 11B–N stretching modes of the linear BNSi molecule, on the basis of the relative intensities of the isotopic features. Again, these vibrational frequencies are in good agreement with ab initio results.