Photo- and radiation-produced H-atoms in acid low temperature glasses containing Fe 2+ ions

Abstract

Frozen solutions of H 2SO 4 and acid 7 M NaClO 4 containing Fe 2+ ions have been exposed to X rays and UV light and examined by EPR methods. It is concluded that the H atoms formed in UV-irradiated acid perchlorate matrices do not have mobile electrons as precursors. Thus no trapped electrons are found after UV irradiation even though these matrices provide efficient traps for electrons. The effect of the electron scavenger NO − 3 is identical in UV- and X-irradiated matrices and largest in the H 2SO 4 matrix. Thus it seems that NO − 3 acts on a similar H-atom precursor in the two cases, and that this precursor may be an excited CTTS state, rather than a mobile electron. The absence of allyl alcohol scavening effect on H atoms produced by UV light in the perchlorate matrix indicates that this H-atom scavenger does not interact with the CTTS state, and that the H atom is trapped in the vicinity of the Fe 2+ ion where it was formed. The presence of small amounts of Fe 2+ ions (< 10 −3 M) in the matrices causes a marked decrease in the spin—lattice relaxation time of the trapped hydrogen atoms as well as a decrease in the intensities of the satellite lines relative to the main hydrogen lines.