X-ray photoemission study of a new allotrope of solid selenium (rhombohedral Se consisting of Se6 ring molecules)

An x-ray photoemission spectrum of a newly found allotrope of solid selenium, rhombohedral Se containing only Se6 ring molecules, has been presented, and compared with those of monoclinic, trigonal, and amorphous forms. The most remarkable points in the density of states of rhombohedral Se are (1) the intensity ratio of the 4p upper bonding band to the lower bonding band is reversed with respect to that of monoclinic Se, and (2) a relatively deep dip is observed at the center of the 4s band. The x-ray photoemission spectra have been analyzed with CNDO/S molecular-orbital calculations. The possibility of the existence of Se6 ring molecules in amorphous Se has been also examined.