AN AB-INITIO MO STUDY OF THE THERMAL-DECOMPOSITION OF CHLORINATED MONOSILANES, SIH4-NCLN (N = 0-4)

The reactants, clusters, transition structures, and products for the various channels for the thermal decomposition of SiH4-nCln were optimized at the HF/6-31G(d) and MP2/6-31G(d,p) levels. The electron correlation contributions were calculated at the MP4/6-31 G(d,p), MP4/6-31+G(2df,p), MP2/6-31++G(3df,3pd), and G-2 levels of theory. In the decomposition of SiH4, SiH2 + H-2 is favored over SiH3 + H. For SiH3Cl, the SiHCl + H-2 channel is preferred over the SiH2 + HCI channel, with fragmentation into SiH2Cl + H and SiH3 + Cl lying significantly higher. The barriers for SiH2Cl2 decomposition are SiCl2 + H-2 almost-equal-to SiHCl + HCI < SiHCl2 + H < SiH2Cl + Cl < SiH2 + Cl2. For SiHCl3, decomposition into SiCl2 + HCI is favored over SiCl3 + H, with the SiHCl2 + Cl and SiHCl + Cl2 channels lying substantially higher. In tetrachlorosilane, SiCl4 --> SiCl3 + Cl is favored over SiCl4 --> SiCl2 + Cl2.