Polymerization of molecular (yellow) arsenic

DTA studies were performed to investigate the polymerization of molecular (yellow) arsenic (y-As), in the dark and also under illumination/irradiation. The semiempirical quantum chemical CNDO/BW method for calculating the dimerization reaction pathway of two As₄ molecules was applied, and showed that the stability of y-As decreases, due to the formation of stable fragments of the polymeric phase (a-As). Using the principle of orbital symmetry conservation, it was shown that polymerization takes place most favourably from a staggered “face-to-face” configuration of As₄ molecules. Dark polymerization proceeds under activation. For a result of the initial stage of polymerization, CNDO/BW simulation predicts the formation of an As₈ dimer. The molecular cluster As₈ of D_2h symmetry forms a six-membered chairshaped ring which constitutes one of the dominating units in the polymeric phase (a-As).