The ionization threshold of N,N,N′,N′-tetramethyl-p-phenylenediamine in dense fluid ethane; effects of fluid density and temperature

The ionization threshold IF of N,N,N′,N′-tetramethyl-p-phenylenediamine in ethane, has been measured in the density (ρ) range 0.15–13.30 M/l and over the temperature (T) range 295–413 K, using a multiphoton ionization conductivity technique. The IF was found to be a function of both ρ and T in the ranges studied. At a fixed T (=373 K), IF was found first to decrease with increasing ρ and then to level off at densities of ∼10 M/l. For ρ≥11 M/l and T=295 K, the IF was found to increase with increasing density. At constant density (ρ=5.90 M/l ) IF decreased with increasing T between 323 and 413 K. These results are analyzed and discussed in relation to the effect of ρ and T on the electron conduction band energy V0 and the medium polarization energy P+. The changes in the IF with ρ are attributed to the dependence of V0 and P+ on ρ, while the dependence of IF on T is attributed to the effects of T on V0 rather than on P+.