Research ArticleASTROCHEMISTRY

Liquid-like behavior of UV-irradiated interstellar ice analog at low temperatures

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Science Advances  29 Sep 2017:
Vol. 3, no. 9, eaao2538
DOI: 10.1126/sciadv.aao2538
  • Fig. 1 Bubbles observed by an optical microscope (Nikon CM-10L) at 128 to 129 K in UV-irradiated amorphous H2O–CH3OH–NH3 ice (H2O/CH3OH/NH3, 5:1:1).

    The elapsed time from the first frame (0 s) (upper left) is shown in each figure, and newly exploded bubbles are indicated by arrows. Bubble growth occurred within a few to several seconds. Scale bars, 200 μm.

  • Fig. 2 Sublimated gases from UV-irradiated interstellar ice analog and its infrared absorption feature.

    (A) Quadrupole mass spectrometer signals of gas species sublimated from the UV-irradiated amorphous H2O–CH3OH–NH3 ice during warm-up. The ion intensities are saturated at 1 × 10−10 A for mass/charge ratios (m/z) = 2, 17, and 18. H2 signal spikes (m/z = 2) were observed at ~60 to 140 K. (B) Infrared spectra of the UV-irradiated (red curve) and non–UV-irradiated (black curve) H2O–CH3OH–NH3 ices at 10 K. The inset shows enlarged spectra of the same samples at 4000 to 4300 cm−1, where the H2 peak in water-rich ice appeared for the UV-irradiated ice.

  • Fig. 3 In situ TEM observation of UV-irradiated amorphous water ice and ice Ic.

    (A) TEM images of amorphous water ice islands, irradiated by UV at 10 K for 50 min, at different temperatures during warm-up (see Materials and Methods and fig. S5 for details about the synthesis of amorphous ice islands). Image contrast shows differences in thickness, and the darker parts represent thicker ice (that is, islands of amorphous ice). The contrast became blurred with increased temperature. Note that the images at different temperatures were taken in different regions of the samples. (B) Wetting process of amorphous water ice (UV irradiation for 50 min at 10 K) at 60 K. The same sample area was observed for over 60 min, and the contrast became blurred with time. (C) Ice Ic observed at 60 K for 60 min without UV irradiation. Islands of ice Ic were made from an ASW film deposited at 6 K by heating at 145 K for 10 min (see Materials and Methods and fig. S5). Observations were made at the same position in the sample. Scale bars, 500 nm (A to C). (D) Schematic of the wetting process.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/9/eaao2538/DC1

    fig. S1. Setup of the PICACHU apparatus for in situ observations of bubbles.

    fig. S2. Successive images of bubble growth (within the area indicated by a dotted circle) at 88 K (run 081) observed by a high-speed optical microscope (Keyence VW-9000) with a long-distance zoom lens (VW-Z2).

    fig. S3. Growth of bubbles at 88 K (run 081) and 112 K (run 056).

    fig. S4. Change in column density of H2 molecules in the UV-irradiated H2O–CH3OH–NH3 ice as substrate temperature increases at a rate of 1 K min−1.

    fig. S5. Formation procedure of amorphous ice islands by UV irradiation of ice Ic with low-magnification TEM images and electron diffraction patterns of the ice.

    fig. S6. Temporal change in the frequency distributions of the relative number of transmitted electrons in TEM images during 60 min of observation of UV-irradiated amorphous water-rich ice (left) and nonirradiated crystalline water-rich ice (right) at 60 K.

    fig. S7. Temperature dependence of the d space of the main halo of electron diffraction patterns of UV-irradiated amorphous water ice.

    table S1. Experimental conditions and summary of bubbling occurrence (y, yes; n, no).

    movie S1. Bubbling of the UV-irradiated amorphous H2O–CH3OH–NH3 ice (H2O/CH3OH/NH3, 5:1:1) at 128 to 129 K.

    Reference (36)

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. Setup of the PICACHU apparatus for in situ observations of bubbles.
    • fig. S2. Successive images of bubble growth (within the area indicated by a dotted circle) at 88 K (run 081) observed by a high-speed optical microscope (Keyence VW-9000) with a long-distance zoom lens (VW-Z2).
    • fig. S3. Growth of bubbles at 88 K (run 081) and 112 K (run 056).
    • fig. S4. Change in column density of H2 molecules in the UV-irradiated H2O–CH3OH–NH3 ice as substrate temperature increases at a rate of 1 K min−1.
    • fig. S5. Formation procedure of amorphous ice islands by UV irradiation of ice Ic with low-magnification TEM images and electron diffraction patterns of the ice.
    • fig. S6. Temporal change in the frequency distributions of the relative number of transmitted electrons in TEM images during 60 min of observation of UV-irradiated amorphous water-rich ice (left) and nonirradiated crystalline water-rich ice (right) at 60 K.
    • fig. S7. Temperature dependence of the d space of the main halo of electron diffraction patterns of UV-irradiated amorphous water ice.
    • table S1. Experimental conditions and summary of bubbling occurrence (y, yes; n, no).
    • Legend for movie S1
    • Reference (36)

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    Other Supplementary Material for this manuscript includes the following:

    • movie S1 (.mp4 format). Bubbling of the UV-irradiated amorphous H2O–CH3OH–NH3 ice (H2O/CH3OH/NH3, 5:1:1) at 128 to 129 K.

    Files in this Data Supplement: