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Mixing of the Immiscible: Hydrocarbons in Water-Ice near the Ice Crystallization Temperature

Lignell, Antti and Gudipati, Murthy S. (2015) Mixing of the Immiscible: Hydrocarbons in Water-Ice near the Ice Crystallization Temperature. Journal of Physical Chemistry A, 119 (11). pp. 2607-2613. ISSN 1089-5639. http://resolver.caltech.edu/CaltechAUTHORS:20141103-074721225

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Abstract

Structural changes in hydrocarbon-doped water-ice during amorphous to crystalline phase conversion are investigated using polycyclic aromatic hydrocarbons (PAHs) as probes. We show that aggregation of impurity molecules occurs due to the amorphous–crystalline transition in ice, especially when they are hydrophobic molecules such as PAHs. Using ultraviolet–visible (UV–vis), Fourier-transform Infrared (FTIR), and laser-induced-fluorescence (LIF) spectroscopic techniques, we show that, although ice infrared absorption features change from a broad structureless band corresponding to amorphous ice to a sharp structured crystalline ice bands, simultaneously, sharper isolated PAH UV absorption features measured in the amorphous ice host turn broad upon ice crystallization. A simultaneous decrease in the monomer fluorescence and increase in the excimer emission band is observed, a clear indication for the formation of PAH molecular aggregates when amorphous ice is converted to crystalline ice at higher temperatures. Similar to the irreversible amorphous–crystalline phase transitions, the UV, fluorescence, and excimer emissions indicate that PAHs undergo irreversible aggregation. Our studies suggest that organic impurities exist as aggregates rather than monomers trapped in crystalline water-ice when cycled through temperatures that convert amorphous ice to crystalline ice, rendering a better insight into phenomena such as the formation of cometary crust. This aggregate formation also may significantly change the secondary reaction pathways and rates in impurity-doped ices in the lab, on Earth, in the solar system, and in the interstellar medium.


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Additional Information:© 2014 American Chemical Society. Received: September 19, 2014; Revised: October 10, 2014; Published: October 10, 2014. This research was enabled through partial funding from the following NASA programs: Planetary Atmospheres, Cassini Data Analysis Programs, Spitzer Science Center, and Astrobiology Institute Node Early Habitable Environments (NASA Ames). JPL’s DRDF and R&TD funding for infrastructure of the “ice spectroscopy laboratory” is also gratefully acknowledged. This research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.
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Record Number:CaltechAUTHORS:20141103-074721225
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20141103-074721225
Official Citation:Mixing of the Immiscible: Hydrocarbons in Water-Ice near the Ice Crystallization Temperature Antti Lignell and Murthy S. Gudipati The Journal of Physical Chemistry A 2015 119 (11), 2607-2613 DOI: 10.1021/jp509513s
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:51150
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:03 Nov 2014 21:03
Last Modified:25 Mar 2019 18:46

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