Crystalline H2O Ice Research Articles

The ice band in IRAS 09371 + 1212

Spectra from 2 to 4 microns of the unusual IRAS source 09371 + 1212, a bipolar nebula, reveal a deep H2O ice absorption band near 3.1 microns. No long-wavelength wing is present, implying that the absorbing grain mantles are of high purity. The structure of the absorption feature is reasonably well modeled by a mixture of amorphous and crystalline H2O ice mantles on silicate grains, but discrepancies remain that could indicate other absorbers also.

Decay kinetics of the ultraviolet and visible luminescences emitted by electron-irradiated crystalline H2O ice

Electron pulse irradiated samples of high purity, crystalline H2O ice at 88 K showed three kinetically distinguishable regions of luminescence emission at 280–340 nm (band I); 320–600 nm (band II); and 450–600 nm (band III). Band II emission was assigned to the A 2∑+→X 2Π transition of OH, the gas phase peak being shifted from 306.4 to ∼385 nm by the ice lattice. The decay half-life of the band II emission resulting from a single, ∼0.05 Mrad electron pulse, was 25±3 ns and increased steeply to 210±10 ns for the second pulse and then steadily decreased to 140±10 ns after 20 pulses. Band II emission from the second or later pulses was resolved into a short lived component with a decay half-life of ∼30 ns and a longer lived component with a half-life of ∼400 ns. The latter decay fitted a second order homogeneous rate equation in which the initial concentrations of the two reactants were in the ratio (2.6±0.1):1 and was attributed to the formation of excited OH by electron–ion recombination in the bulk ice. The short lived band II emission was also attributed to excited OH and probably arose from a mixture of a fast intraspur recombination reaction with some other process of different reaction order. Dose accumulation (memory) effects were attributed to the accumulation of OH radicals and lattice vacancies in the irradiated ice. The band III emission had a half-life of 25±5 ns and its decay kinetics were consistent with emission from species such as excited OH− or H3O produced when electrons tunnel from a trapping site to a geminate partner.

Subdivision of the Luminescence Spectrum of Irradiated Crystalline H 2 O Ice

The luminescence emitted when crystalline H2O ice at 88 K is irradiated with pulsed electrons has been subdivided into the following three spectral bands at wavelengths, λ, and photon yields, Gp, by using the measured dependence of emission intensity on accumulated dose. Band I: λ = 280-340 nm, Gp = 2 × 10−7 photons/100 eV. Band II: λ = 320-600 nm, Gp = 1 × 10−5 photons/100 eV initially but accumulating to a plateau value of 2× 10−4 photons/100 eV at an absorbed dose of 1.2-1.5 Mrad. Band III: λ = 500-600 nm,Gp = 1 × 10−5 photons/100 eV.