Kinetics in ices with complex compositions
EMSL Project ID
2398
Abstract
Our description of the role played by ice particles in altering the chemical composition of the Earth's atmosphere is currently undermined by our poor understanding of the interaction of molecules with ice surfaces. Tackling the complex coupled kinetics responsible for interfacial reactivity (adsorption and desorption, surface and bulk diffusion, reaction, phase separation and crystallization) has proven a daunting task even for idealized systems. However, it has become increasingly clear that any further progress in our understanding of heterogeneous atmospheric chemistry will require a quantitative description of the still controversial adsorption state (molecularly adsorbed or ionically dissociated) of atmospherically relevant molecules on ice surfaces. This issue has come into the spotlight recently because of the postulated reactivity of the resulting partially hydrated, surface segregated halide anions towards gas phase species. It has been proposed that this mechanism could initiate the well-known ozone consuming catalytic cycles in the polar stratosphere [1-3]. These issues are also intimately coupled to other outstanding problems in the chemistry and physics of ice such as impurity uptake and diffusion, as well as the phase separation and crystallization kinetics for various hydrates from icy material with complex compositions. Our approach will use thin films as models for atmospherically relevant systems. We will perform quantitative studies of the complex coupled kinetics in water-acid binary ices with a particular emphasis on uptake, diffusion, phase separation and crystallization in the HCl-water system. The best approach to undertake this ambitious endeavor requires a combination of molecular beam and thermal desorption techniques, complemented with simultaneous in situ characterization by vibrational spectroscopy. These investigations will be performed in the molecular beam-surface scattering and kinetics instrumentation available in the laboratories lead by Bruce Kay. Analogous studies on the alcohol-water and helium-water binary systems were undertaken jointly with Bruce Kay, Scott Smith, Greg Kimmel, Zdenek Dohnalek, John Daschbach and Glenn Teeter during the applicant's postdoctoral work (with partial support from NSERC-Canada in the form of a postdoctoral fellowship). The applicant therefore has considerable experience in the operation of this elaborate instrumentation and wishes to maintain this collaborative interaction as a complement to his academic research program at the Universit? de Sherbrooke beginning in December 2001. Additionally, computer control and data acquisition software developed by the Instrument Development Laboratory (specifically, Surf-O-Matic) will be deployed in Sherbrooke. References [1] E. M. Knipping, et al., Science 288, 301-306 (2000). [2] S. L. Richardson, et al., Chem. Phys. Lett. 270, 395-398 (1997). [3] A. K. Huff and J. P. D. Abbatt, J. Phys. Chem. A 104, 7284-7293 (2000).
Project Details
Project type
Exploratory Research
Start Date
2002-01-01
End Date
2005-01-06
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members