EFFECT OF HIGH-PRESSURE ON PHOTOIONIZATION OF N,N,N',N'-TETRAMETHYL-P-PHENYLENEDIAMINE (TMPD) IN LIQUID 2,2-DIMETHYLBUTANE (DMB)

The effect of high pressure on the photoionization of N,N,N',N'-tetram ethyl-p-phenylenediamine (TMPD) in liquid 2,2-dimethylbutane (DMB) was studied by measuring the photoconductivity. The pressure dependence o f the cationic polarization energy, estimated from the threshold energ ies of photoconduction and from values of the electron affinity of the solvent, does not follow Born's formula if the macroscopic dielectric constant is used. This seems to indicate that in the threshold region only molecules where the local density around the solute molecule is higher than average can be ionized. The maximum local density was esti mated by taking into account density fluctuations. With this model, ag reement with the experimental results could be obtained. The effect of high pressure on the apparent ionization quantum yield and on the sha pe of photoconductivity spectrum is discussed.