DETAILED STUDIES OF A ONE-ELECTRON 2-PHOTON IONIZATION IN A RIGID ORGANIC SOLUTION AT 77 DEGREES K

A quantitative spectrophotometric study is made of the photoionization of N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD) in 3-methylpentane (3MP) rigid solution at 77°K. Some extension is also made to an ether-isopentane-ethanol (EPA) rigid solution. The ionization is shown to proceed by a biphotonic mechanism with the metastable triplet state as the second photon-absorbing intermediate. It is further shown by polarization measurements that ionization of the triplet state occurs by direct excitation into the continuum or near continuum. Quantitative estimations are obtained and wavelength dependence is determined for the quantum efficiencies of both one-photon steps.