STRUCTURAL INVESTIGATION OF MOLECULES IN THE VAPOR OVER BERYLLIUM DICHLORIDE USING ELECTRON-DIFFRACTION AND MASS-SPECTROMETRIC DATA

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 th e ratio 97.5:2.5. Molecular parameters were refined for both molecules from GED data. The equilibrium structure of BeCl2 is linear with the bond length r(e)(anh)(Be-CI) = 1.791(5) Angstrom. The thermal-average bond length r(g)(Be-Cl) is 1.798(4) Angstrom. Relations between differ ent kinds of the refined parameters (r(a), r(alpha), r(e)(h), r(e)(ch) , r(e)(anh)) are discussed. Force constants and vibrational frequencie s were obtained for this molecule from GED data alone. Assuming D-2h s ymmetry the following parameters were obtained for Be2Cl4: r(g)(Be-Cl- t) = 1.828(14) Angstrom r(g)(Be-Cl-b) = 1.968(20) Angstrom, angle(alph a)(Cl-t-Be-Cl-b) = 134(4)degrees. The force constants and frequencies for the dimer were estimated.