SINGLE-PHOTON IONIZATION OF PYRENE AND ANTHRACENE GIVING TRAPPED ELECTRONS IN ALKALI-METAL-CATION-EXCHANGED ZEOLITE-X AND ZEOLITE-Y - A DIRECT TIME-RESOLVED DIFFUSE REFLECTANCE STUDY

Time-resolved diffuse reflectance spectroscopy is used to investigate the photolysis of anthracene- or pyrene-impregnated alkali-metal-cation-exchanged zeolite X and Y with a nitrogen laser (337 nm). The studies suggest that anthracene or pyrene molecules are distributed in at least two different sites (active and nonactive) in the zeolites X and Y. Excitation of anthracene or pyrene adsorbed in nonactive sites produces singlet excited states of anthracene or pyrene, which can either be photoionized by absorbing a second photon or decay to the triplet excited states through intersystem crossing; however, anthracene or pyrene adsorbed in active sites is photoionized through a single-photon process. The products of the photoionization are cation radicals of arene and trapped electrons (e.g., Na4(3+) for NaY). The broad absorption band for the trapped electron is around 550 nm for both NaX and NaY; around 620 nm for both LiX and LiY and around 710 nm for KX.