COMPARISON OF UV-VISIBLE AND UV-IR 2-COLOR MULTIPHOTON IONIZATION OF BENZO[A]PYRENE IN NORMAL-HEPTANE - PHOTOCURRENT INVESTIGATIONS

Photocurrent signals induced by the cooperative action of 355 nm (UV) and 532 nm (visible) or of 355 nm and 1064 nm (IR) pulsed laser lights were compared for benzo[a]pyrene in n-heptane. The additional action of the visible light enhanced the photocurrent signal more effectively than that of the IR light at a constant photon flux. The photocurrent enhancement was observed even when the visible light arrived 20 ns after the UV light, and was affected by air. A delay of 20 ns of the IR light induced no photocurrent enhancement. The effects of perfluorohexane on the photocurrent enhancements were investigated. It is suggested that the IR light acts through the geminate cation-electron pair, while the visible light acts mainly through the first excited singlet state.