X-ray-absorption near-edge-structure studies in hexamethylenetetraselenafulvalene (HMTSF) and HMTSF-tetracyanoquinodimethane (HMTSF-TCNQ) and -tetrafluorotetracyanoquinodimethane (HMTSF-TFTCNQ)

We report the first x-ray-absorption measurements on conducting charge-transfer salts, using synchrotron radiation. By measuring the Se K x-ray-absorption near-edge structure (XANES) of hexamethylenetetraselenafulvalene (HMTSF)0 and fully charge-transferred HMTSF-tetrafluorotetracyanoquinodimethane (HMTSF-TFTCNQ) and comparing the results with those on partially charge-transferred HMTSF- tetracyanoquinodimethane (HMTSF-TCNQ), we conclude that the charge on the cation stack in the latter is delocalized as opposed to being concentrated on discrete sites of a generalized Wigner lattice. © 1984 The American Physical Society.