Radioluminescence of H2O and D2O ice

Abstract

The luminescence emitted during x‐ray irradiation of H₂O and D₂O ice at 77 K exhibits an identical emission band peaked at 373 nm. D₂O also exhibits a band peaked at 534 nm which is not seen for H₂O. The 373 nm band appears to have a decay time in the range 10⁻⁴–10⁻³ sec, whereas the 534 nm band decays completely in less than 10⁻⁴ sec. The emission yield is G∼2×10⁻² and G∼2×10⁻³ for D₂O and H₂O, respectively. The yield of the peak at 373 nm is significantly increased by NaCl, NaBr, NaI, and HCl in concentrations above 10⁻³M, whereas the 534 nm band in D₂O is not affected by any of these additives. AgNO₃, H₂O₂, and NaNO₃ reduce the emission yield whereas other efficient electron and OH scavengers like CCl₃COONa and acrylamide do not affect the luminescence even in concentrations of 1M. The identity of the luminescent species is obscure. The scavenger effects indicate that it has a mobile precursor which is not electrons or OH and probably not H atoms. The emission yields, as well as the decay time of the 373 nm band, decrease with increasing temperature. The 373 nm band is more sensitive to heating than the 534 nm band. In mixtures of D₂O and H₂O the emission yields fall off more rapidly with increasing H₂O concentration than expected if the emissions from D₂O and H₂O were additive. This effect is consistent with the assumption that the differences between H₂O and D₂O are largely due to quenching processes that are more efficient in H₂O.