Cover Page/Proposal Summar>

ROSS-99    NRA 99-OSS-01

Date Due: 5/3/99

We propose to extend and complete our measurement programs of (a) the absorption cross sections of ultraviolet SO2 transitions, and (b), the band and line oscillator strengths and line widths of N2 transitions in the VUV region. These laboratory projects are in support of efforts to interpret and model observations of the atmospheres of Io and Venus, and Titan and Triton, respectively. Our SO2 laboratory program is designed to provide astronomers with high-resolution cross section data for the complex SO2 ultraviolet absorption spectrum. Our highest priority is to complement our recent measurements of SO2 cross sections at T=295 K with measurements in the 197 to 245 nm region at T=155 K. These low temperature cross sections are critical for the interpretation of SO2 features in the atmosphere of Io. We will also extend the wavelength coverage of our previous room temperature measurements (198 to 220 nm) to coincide with the wavelength range for the proposed low temperature measurements. We also plan to initiate room temperature and low temperature measurements in the 280 to 320 nm region. All measurements will be undertaken with a resolving power of 450,000; a factor of 5 better than the highest resolution measurements available in the literature. The goal of our N2 laboratory program is the measurement of fundamental parameters of the absorption spectrum in the 80 to 100 nm region. We use high-resolution (R=120,000) measurements to determine band and line f-values and line widths. Presently, published band f-values for the 100 bands in this region are incomplete and inconsistent, very few line f-values have been measured, and line widths are known for only a small fraction of the transitions. Our N2 measurement program is designed to support the analyses of planetary occultation observations (Voyager UVS - Titan and Triton; Cassini UVIS - Titan) and airglow observations of Titan (Voyager UVS, Cassini UVIS, FUSE).