Our research focuses on the measurement and modeling of vacuum ultraviolet and UV molecular photoabsorption cross sections with the highest practical resolution and accuracy. IT supports efforts to…

This federal award to Wellesley College is a $305,719.40 grant from the National Aeronautics and Space Administration (NASA) for research related to measuring and modeling vacuum ultraviolet and UV molecular photoabsorption cross sections. The research focuses on isotopologues of CO2, O2, and CO, as well as N2, to support efforts to interpret, model, and understand observations of planetary atmospheres, particularly the Martian atmosphere. This work responds to the specific data needs of ongoing NASA missions. The research will be conducted at the SOLEIL synchrotron facility and the results will be archived with NASA's Planetary Data System. This grant does not have a set-aside designation.

Our research focuses on the measurement and modeling of vacuum ultraviolet and UV molecular photoabsorption cross sections with the highest practical resolution and accuracy. IT supports efforts to interpret, model, and understand observations of planetary atmospheres, and IT responds to the specific data needs of ongoing NASA missions. We request funding to support laboratory work on the isotopologues of CO2, O2, and CO and on N2, with current martian atmosphere applications being the primary drivers. CO2, O2, and CO: isotope ratios of atmospheric species reveal much about the evolution of a planet S atmosphere and volatile reservoirs. We focus here on the O and C isotopologues of CO2, O2, and CO in the martian atmosphere. Present-day isotopic ratios in the martian atmosphere are signatures of the long-term evolution of the atmosphere and climate. Isotopic fractionation in the photodissociation of CO2 and O2 is expected to strongly influence the 16O/17O/18O composition of the atmosphere, while photodissociation of CO is the primary photochemical source of the escape of atomic carbon from mars. The quantitative interpretation of ongoing observations of the martian upper-atmosphere isotopic composition by the maven ngims instrument requires detailed knowledge of isotope-selective processes during photodissociation. These in turn require accurate isotopic cross sections. We propose to: a) measure the cross sections of the relevant CO2 isotopologues (13C16O2, 12C16O17O, and 12C16O18O) from the ionization limit, 90 NM, to 190 NM; B) measure the cross sections of O2 isotopologues at lyman-alpha (121.6 NM) to verify predictions of strong fractionation effects associated with this strong solar feature; C) measure cross sections of 12C16O and 13C16O from 91.2 NM to approximately 80 NM to support evaluations of strong 12C/13C fractionation in the photochemical origin of atomic carbon escape from mars following photodissociation of CO. The proposed measurements will be carried out on the desirs beamline of the soleil synchrotron, the premier facility in the world for gas-phase high-resolution photoabsorption measurements. CO cameron bands and N2 LBH bands: the cameron bands of CO are prominent middle-ultraviolet airglow emission features of mars, and the lyman-birge-hopfield (LBH) bands of N2 were recently observed in emission in the martian upper atmosphere by the iuvs on maven. LBH bands also dominate the VUV airglow emissions from titan's upper atmosphere; the analysis of their prominence has long been a central component of upper-atmospheric models of the N2-rich atmospheres of earth, titan, triton and pluto. The distribution of radiant energy within the CO and N2 bands provides insight into temperatures, pressures, and densities as well as the distributions of electron and ION energies as functions of altitude. The interpretation of the emission intensities relies on a suite of electron-impact excitation and emission cross section measurements for relevant gases. The extractions of these cross sections from the laboratory data are susceptible to subtle, but important, effects associated with the dipole-forbidden nature of the CO cameron and LBH transitions. We are initiating a collaborative effort with DR. Charles malone (JPL), a key author on the most recent relevant laboratory studies of electron-impact on CO and N2 excitation and emission, to measure the photoabsorption cross sections of the cameron and LBH bands at to apply our measurements to improve the accuracy of he cameron and LBH emission cross sections. The proposed research contributes to the pdart program via the generation of new reference information (scope of program element 1.5). The spectroscopic data are directly relevant to ongoing martian atmospheric research and are also intended for general use in planetary science. We will archive our data via the atmospheres node of the NASA PDS.