THE PHOTOIONIZATION SPECTRUM OF LIQUID BENZENE

The photocurrent from neat liquid benzene has been studied for excitat ion energies from threshold to 10.3 eV and for externally applied elec tric fields from 1 to 50 kV/cm, Using a power law fit to the energy de pendence of the threshold current, an onset of epsilon(t) = 7.65 +/- 0 .1 eV has been obtained. The field dependence was fit to an exponentia l radial probability density for thermalized ion-pair separation dista nces with an average separation distance of (r) = 23 +/- 2 Angstrom at an excitation energy, epsilon, of 8.86 eV (1.2 eV above threshold). P hotocurrent was too weak to establish a dependence of (r) on excitatio n energy. The quantum yield for photocurrent at 8.86 eV was determined by comparison with the photocurrent from TMPD in 2,2,4-trimethylpenta ne (isooctane) to be 6.5 x 10(-4) at zero field. From this, the intrin sic molecular ionization probability at epsilon = 8.86 eV was determin ed to be 0.6 +/- 0.3.