Knowledge Bank

Spectroscopic studies of small crystalline solids have been made by a specially designed near-normal reflection spectrometer. With this instrument, electronic transitions have been studied in a new group of stable ion-radical salts based on the strong $\pi$-acid 7,7,8,8-tetracyanoquinodimethan [FIGURE] The observed electronic transitions in TCNQ and the morpholinium, cesium, and triethylammomum salts of TCNQ will be interpreted in terms of a simple molecular orbital picture of the isolated molecule or of aggregates of 2, 3, or 4 molecules with ''face-to-face'' orientation. Although this model is obviously naive in many respects, it does provide for some interesting speculation with regard to the type of intermolecular forces involved in these ion-radical solids.