EUV ABSORPTION SPECTROSCOPY OF SUPERSONIC-JET-COOLED MOLECULES: CO BANDS IN THE WAVELENGTH REGION $\sim$97 nm

This work is supported by NASA grant NAGW 1596 to Harvard College ObservatoryAuthor Institution: Harvard-Smithsonian Center for Astrophysics; Physics Department, Wellesley College; Photon Factory, KEKSpectra obtained at 295 K show that many CO bands below 100 nm are both overlapped and perturbed. As a consequence, synthetic EUV absorption spectra for CO at the low temperatures that prevail in interstellar clouds are uncertain. In order to simplefy and clarify such band systems, we have developed a supersonic jet expansion apparatus that is used with the 6.65-m vacuum spectrometer at the Photon Factroy, KEK, Japan. A predispersed beam of synchrotron radiation enters a 3-mm diameter hole close to the supersonic jet and defines a section of the jet stream to record molecular absorption. A mixture of carbon monoxide in helium is used. The absorption spectrum of CO at $\sim$25 K in the wavelength region $\sim$97 nm has been investigated photoelectrically with this apparatus. The measured spectrum at $\sim$25 K is in resonable agreement with some published modelled spectra, but our ratios of integrated cross sections of those bands are somewhat different from those determined from low resolution spectra obtained at 295 K