Photoelectrons in Rb/THF solution: Spectral dependence of photodetachment cross-section

Photoconductivity method, combined with laser pulse excitation, was employe d to obtain the spectral dependence of electron photodetachment in rubidium -tetrahydrofuran (Rb/THF) solution at room temperature. Wavelength dependen ce of photodetachment cross section, sigma (pd), qualitatively retraces tha t of the optical absorption cross section, a,. Moreover, a wavelength depen dence of the quantum yield, kappa = sigma (pd)/sigma (a),was also found, wh ere kappa approximate to 0.03 is held constant for the wavelengths region l ambda greater than or equal to 680 nm (hv less than or equal to 1.8 eV). Al so, in the short wavelengths region, lambda less than or equal to 510 nm (h v greater than or equal to 2.4 eV), K is constant, but almost three times l arger (K x 0.085). The inflection region is located approximately at hv = 2 .2 eV, that coincides with the energy of Rb ground state relative to the lo wer edge of the conduction band of THF. Mechanism of Charge-Transfer-To-Sol vent (CTTS) with a subsequent release of a solvated electron is suggested t o be valid below the conduction band of Rb/THF. It implies that kappa = k(s )/(k(s) + k(c)) approximate to 0.03, and consequently, k(c) = 30k(s), where k(c) is the rate constant of the radiationless interconversion, and k, is the rate constants of the isomerization of CTTS excited state with the form ation of the solvated electron. When photon energy becomes higher than the energetic gap between the CTTS ground state and the edge of the THF conduct ion band, photoinduced autoionization transitions into the continuum genera te quasi-free electrons.