Knowledge Bank

“Anthracene-tritrobenzene (A-TNB) and $Cs2(TCNQ)3\ast$ ion-radical sat single crystals have been studied spectroscopically by a font reflectance technique at temperatures down to $4.2^{\circ} $K. The polarized infrared reflectance spectra of A-TNB show essentially no changes in the vibrational frequencies of the parent molecules; the $Cs2(TCHQ)3$ salt results show, by contrast, marked changes in intensity and frequency from the vibrational spectra of the neutral TCNQ molecule. In addition, Raman active modes of the neutral molecule appear to become infrared active in the ion-redical salt and are polarized roughly ````out-of-plane’’’’ with respect to the molecule. These results will be discussed in terms of an electrons vibration’’ model proposed by Ferguson for other charge-transfer $solids.^{1}$ If the $Cs_{2}(TCNQ)_{3}$ ion-radical salt is thought of in terms of an extension of charge-transfer formalism, then out-of-plane’’ dipole transitions may be pictured as arising from in-plane’’ molecular vibrations. For the more severe skeletal distortional modes such as the Raman active totally symmetric stretch ($A_{1g}$), the electron vibration’’ effect is likely to be the more significant. The lack of evidence for this effect in A-TNB may be taken as an indication of the relatively small amount of charge-transfer interaction in this solid as compared with the cesium salt.”