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PULSED INFRARED DESORPTION OF CO2 GUEST MOLECULES
IN AMORPHOUS SOLID WATER
by
Oscar R. Rebolledo-Mayoral
A Dissertation Presented to the FACULTY OF THE USC GRADUATE SCHOOL UNIVERSITY OF SOUTHERN CALIFORNIA In Partial Fulfillment of the Requirements for the Degree DOCTOR OF PHILOSOPHY (CHEMISTRY (CHEMICAL PHYSICS))
August 2011
Copyright 2011 Oscar R. Rebolledo-Mayoral
Object Description
| Title | Pulsed infrared desorption of carbon dioxide guest molecules in amorphous solid water |
| Author | Rebolledo-Mayoral, Oscar R. |
| Author email | or.rebolledo@gmail.com;rebolled@usc.edu |
| Degree | Doctor of Philosophy |
| Document type | Dissertation |
| Degree program | Chemistry (Chemical Physics) |
| School | College of Letters, Arts And Sciences |
| Date defended/completed | 2011-06-08 |
| Date submitted | 2011-07-14 |
| Date approved | 2011-07-15 |
| Restricted until | 2011-07-15 |
| Date published | 2011-07-15 |
| Advisor (committee chair) |
Reisler, Hanna Wittig, Curt |
| Advisor (committee member) | Kresin, Vitaly |
| Abstract | The trapping and release of CO₂ from thin films of amorphous solid water (ASW), < 500 monolayers (ML), were investigated by irradiating vapor-deposited ASW/CO₂ mixtures with pulsed 3424 cm⁻¹ infrared radiation and detecting the ejected molecules using time-of-flight mass spectrometry (TOF-MS). The studies were concerned with the preferential removal of CO2 over H₂O after consecutive low energy radiation pulses (< 1.2 mJ/pulse), and the ejection of water aggregates with high energy pulses (> 1.2 mJ/pulse) which were ionized to protonated water clusters of the form (H₂O)nH⁺ with n = 1 – 6. ❧ Amorphous solid mixtures of ASW/CO₂ with typical composition ratios of 3:1 or 4:1 (H₂O:CO₂) were prepared by co-depositing CO₂ during ASW formation on a MgO(100) substrate. Porous ASW was formed by dosing the MgO substrate with gaseous H₂O at 90 K under ultra-high vacuum conditions. CO₂ multilayers that formed atop the ASW/CO2 film were removed by annealing the film to ~ 112 K and returning it to 90 K. Ablation was achieved through vibrational excitation of the asymmetric stretch of H2O molecules in the ice film. The 3424 cm⁻¹ light was generated by optimizing the second Stokes component in the stimulated Raman scattering (SRS) of 1064 nm radiation from a Nd:YAG laser (10 ns pulses) in D2 (ν = 2987 cm⁻¹). The overall quantum Raman conversion efficiency of ~ 4% was obtained. ❧ Single-pulse irradiation of ASW and H₂O/CO₂ amorphous mixtures resulted in the ejection of both species with high translational energies. The rapid temperature increase after irradiation facilitates CO2 removal via evaporation prior to segregation of CO₂. The high thermal conductivity of the crystalline substrate quenches the heterogeneous nucleation of cavities that take place near the substrate. The presence of small protonated water clusters is interpreted as evidence for trivial fragmentation occurring near the surface of the film. ❧ Despite the significant energy transfer to the substrate, near complete removal of CO2 has been measured through consecutive pulses incident on the same location at the film’s surface. CO₂ removal occurred in as few as 6 pulses, whereas only 10 – 20 ML of H₂O were removed per pulse. The ability of the ice to trap CO₂ changes after each pulse. Whereas the first pulse irradiates an amorphous film, consecutive irradiation of film can induce irreversible changes to the morphology of the irradiated volume thereby inducing partial crystallization. ❧ Future experiments are aimed at exploring guest-host interactions after irradiation, where energy deposition occurs in less time than the characteristic time for thermal transfer to the substrate. Studies where transport and segregation of dopants play a pivotal role in the enhancement of phase explosions and where the energetic release of aggregates through morphology changes is exploited to achieve lift-off of large surface-bound species are also outlined. |
| Keyword | ablation; amorphous solid water; ASW; laser induced desorption; stimulated Raman scattering; time of flight |
| Language | English |
| Part of collection | University of Southern California dissertations and theses |
| Publisher (of the original version) | University of Southern California |
| Place of publication (of the original version) | Los Angeles, California |
| Publisher (of the digital version) | University of Southern California. Libraries |
| Provenance | Electronically uploaded by the author |
| Type | texts |
| Legacy record ID | usctheses-m |
| Rights | Rebolledo-Mayoral, Oscar R. |
| Access conditions | The author retains rights to his/her dissertation, thesis or other graduate work according to U.S. copyright law. Electronic access is being provided by the USC Libraries in agreement with the author, as the original true and official version of the work, but does not grant the reader permission to use the work if the desired use is covered by copyright. It is the author, as rights holder, who must provide use permission if such use is covered by copyright. The original signature page accompanying the original submission of the work to the USC Libraries is retained by the USC Libraries and a copy of it may be obtained by authorized requesters contacting the repository e-mail address given. |
| Repository name | University of Southern California Digital Library |
| Repository address | USC Digital Library, University of Southern California, University Park Campus MC 7002, 106 University Village, Los Angeles, California 90089-7002, USA |
| Repository email | cisadmin@usc.edu |
| Archival file | uscthesesreloadpub_Volume71/etd-RebolledoM-68.pdf |
Description
| Title | Page 1 |
| Full text | PULSED INFRARED DESORPTION OF CO2 GUEST MOLECULES IN AMORPHOUS SOLID WATER by Oscar R. Rebolledo-Mayoral A Dissertation Presented to the FACULTY OF THE USC GRADUATE SCHOOL UNIVERSITY OF SOUTHERN CALIFORNIA In Partial Fulfillment of the Requirements for the Degree DOCTOR OF PHILOSOPHY (CHEMISTRY (CHEMICAL PHYSICS)) August 2011 Copyright 2011 Oscar R. Rebolledo-Mayoral |
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