Abstract
This work reports the pressure dependence of the Raman spectra of TCNQ0, TTF0, K(TCNQ), Cs2(TCNQ)3, perylene–TCNQ, and phenazine–TCNQ in the range from 0 to 70 kbar. By using the average compressibility of ∼0.01 kbar−1 of TTF–TCNQ, approximate mode Grüneisen parameters are derived spanning a range of several orders of magnitude. In the gas phase spectrum of TCNQ, low lying internal modes are observed at 40, 76, and 145 cm−1, lowering the so far assumed demarcation between internal and external modes from about 200 cm−1 down to less than 50 cm−1. From the pressure and gas phase data it is concluded that all of the observed low frequency modes in this class of compounds actually are modes of mixed internal and external character. In TTF0 and TCNQ0 a continuous change in color from yellow to dark red is observed when pressure is applied until the samples become opaque at about 80 kbar. Furthermore, TCNQ shows a phase transition at 12 kbar.
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