Structural investigation of molecules in the vapour over beryllium dichloride using electron diffraction and mass spectrometric data

Abstract According to the data of simultaneous gas-phase electron diffraction (GED) and mass spectrometric (MS) experiments the vapour over beryllium dichloride at 547 K consists of monomeric and dimeric molecules in the ratio 97.5:2.5. Molecular parameters were refined for both molecules from GED data. The equilibrium structure of BeCl 2 is linear with the bond length r anh e ( BeCl ) = 1.791(5) A . The thermal-average bond length r g (BeCl) is 1.798(4) A. Relations between different kinds of the refined parameters ( r a , r α , r h e , r ch e , r anh e ) are discussed. Force constants and vibrational frequencies were obtained for this molecule from GED data alone. Assuming D 2h symmetry the following parameters were obtained for Be 2 Cl 4 : r g ( BeCl t = 1.828(14) A , r g ( BeCl b = 1.968(20) A , ∠ α (Cl t BeCl b = 134(4)°. The force constants and frequencies for the dimer were estimated.