The Crystal Structure of Orpiment

Abstract

The structure of orpiment (As₂S₃) has been analysed using X-ray methods (Weissenl erg and oscillation photographs, Co Ka, λ=1.79A) . The unit cell has the dimensions, a=11.46A, b=9.66A, c=4.21A, β=90°, containing four molecules of As₂S₃. The space groap is C⁵_2A-P2₁/n, with reflexions (hOl) and (OkO) being absent respectively when h+l. and k are odd. The structure is comnosed of As₂S₃ layers held together by the weak van der Waals force. In the layer Asa toms are surrounded by three S atoms. S atoms are always shared by two As atoms. The interatomic distances and bond angles agree with ones in other compounds containing S and As.