抄録
Light-induced phase transformation from realgar to pararealgar has been studied by means of single-crystal X-ray diffraction and X-ray photoelectron spectroscopy. The photochemical degradation causes the increase of As4S4 intermolecular distances and the production of the As4S5 molecules. The results suggest the following cyclic process. 1st : an S atom in the As4S5 is released from one of the As-S-As linkages in As4S5 which becomes the As4S4 pararealgar molecule, 2nd : the free S atom is re-attached to another As4S4 realgar molecule and reproduces an As4S5 molecule, and 3rd : the As4S5 is again divided into an As4S4 pararealgar molecule and an S atom.
