1 research outputs found
UV photoprocessing of CO2 ice: a complete quantification of photochemistry and photon-induced desorption processes
Ice mantles that formed on top of dust grains are photoprocessed by the
secondary ultraviolet (UV) field in cold and dense molecular clouds. UV photons
induce photochemistry and desorption of ice molecules. Experimental simulations
dedicated to ice analogs under astrophysically relevant conditions are needed
to understand these processes. We present UV-irradiation experiments of a pure
CO2 ice analog. Calibration of the QMS allowed us to quantify the
photodesorption of molecules to the gas phase. This information was added to
the data provided by the FTIR on the solid phase to obtain a complete
quantitative study of the UV photoprocessing of an ice analog. Experimental
simulations were performed in an ultra-high vacuum chamber. Ice samples were
deposited onto an infrared transparent window at 8K and were subsequently
irradiated with a microwave-discharged hydrogen flow lamp. After irradiation,
ice samples were warmed up until complete sublimation was attained. Photolysis
of CO2 molecules initiates a network of photon-induced chemical reactions
leading to the formation of CO, CO3 ,O2 , and O3 . During irradiation,
photon-induced desorption of CO and, to a lesser extent, O2 and CO2 took place
through a process called indirect desorption induced by electronic transitions
(DIET), with maximum photodesorption yields (Ypd) of 1.2 x 10-2
molecules/incident photon , 9.3 x 10-4 molecules/incident photon , and 1.1 x
10-4 molecules/incident photon , respectively. Calibration of mass
spectrometers allows a direct quantification of photodesorption yields instead
of the indirect values that were obtained from infrared spectra in most
previous works. Supplementary information provided by infrared spectroscopy
leads to a complete quantification, and therefore a better understanding, of
the processes taking place in UV-irradiated ice mantles