Cover Page/Proposal Summary

ROSS-99    NRA 99-OSS-01

Date Due: 5/3/99

NASA PROCEDURE FOR HANDLING PROPOSALS

This proposal shall be used and disclosed for evaluation purposes only, and a copy of this Government notice shall be applied to any reproduction or abstract thereof. Any authorized restrictive notices that the submitter places on this proposal shall also be strictly complied with. Disclosure of this proposal for any reason outside the Government evaluation purposes shall be made only to the extent authorized by the Government.

Confirmation # 00-011   Date Received: Apr 05, 1999

Proposal Type: New Proposal

Proposal Category: Atmosphere Structures and Particles

Major Equipment Proposal? No

Do you intend to submit an Education/Public Outreach (E/PO) proposal? No

Proposal Title:
Laboratory Studies of Low Temperature Rate Coefficients: The Atmospheric Chemistry of the Outer Planets and Titan

Abbreviated Proposal Title:
Low Temperature Rate Coefficients for Titan

Principal Investigator:
Dr. Stephen Leone
JILA Joint Inst for Lab Astrophys
Univ. Colorado
Campus Box 440
Boulder, CO 80309-0440
Phone: 303-492-5128   Fax: 303-492-5504   E-mail: srl@jila.colorado.edu

SignatureDate
_________________________________________________

Co-Investigators and Collaborators:
NONE


Proposal Summary:

Laboratory measurements have been carried out with the previous NASA grant No. NAG5-4314 to determine low temperature chemical rate coefficients of ethynyl radical (C2H) for the atmospheres of the outer planets and their satellites. This effort is directly related to the Cassini mission which will explore Saturn and Titan. A laser-based photolysis/infrared laser probe setup was used to measure the temperature dependence of kinetic rate coefficients from 150 to 350 K for C2H radicals with H2, C2H2, CH4, CD4, C2H4, C2H6, C3H8, n-C4H10, i-C4H10, neo-C5H12, C3H4 (methylacetylene and allene), HCN, and CH3CN. The results revealed discrepancies of an order of magnitude or more compared with the low temperature rate coefficients used in present models. A new Laval nozzle, low Mach number supersonic expansion kinetics apparatus has been constructed, resulting in the first measurements of neutral C2H radical kinetics at 90 K and permitting studies on gases with insufficient vapor pressures at low temperatures. A new three year program of study is proposed to measure laboratory rate coefficients at the low temperatures relevant to the atmosphere of Titan, from 70-180 K, and the outer planets. New studies in the first year will investigate the reactions of C2H with a series of saturated and unsaturated hydrocarbons. These studies will obtain not only rate coefficient information, but also branching ratios. In the second and third years we will study the reactions of C2H with nitrogen and oxygen-containing compounds, such as HCN and CH3CN, O2 and H2O, and reactions of C3N with hydrocarbons, to investigate the coupling of carbon chemistry with nitrogen/oxygen in the atmospheres of the outer planets. Additional investigations will address studies of low temperature radical recombination (synthesis) reactions and clustering. Precise kinetic rates, which in many cases can presently only be obtained by estimates, will be measured accurately for the first time.