Force constant calculations for pyramidal four-atom molecules—II Pyramidal ZXY2 molecules CH3AsX2 and (CH3)2AsX (X  Cl, Br)

General valence force constants of CH₃AsX₂ and (CH₃)₂AsX (with X  Cl, Br) have been derived from the experimental vibrational spectra and the molecular parameters, applying the FG matrix method of Wilson.

As the approximation of Venkateswarlu and Sundaram for molecules of the type ZXY₂ could not stand here, an adapted framework of F matrix elements is proposed. The group of physically acceptable force constants in this series of analogous XY₃ and ZXY₂ molecules is discussed.