Knowledge Bank

Structural changes as a function of the torsional angle about the central A-A bond have been studied for $X3A-AX3$ molecules with $A=C,Si,Ge$ and $X=H,F,Cl$ and for $X2A=AX2$ molecules with $A=N,P$ and $X=H,F,Cl$ by ab initio calculations. Double or triple zeta basis sets with added polarization functions have been used. The results are compared with experimental values where the latter are available. Simple empirical formulas are presented for simulation of the structure changes and the implications are discussed for analysis of experimental structural determinations by spectroscopy or electron diffraction.