The role of photon stimulated desorption in the release of Ca from the surface of Mercury has been studied. Specifically, 355 nm photon-stimulated desorption of Ca and Ca+ from CaS was examined using time-of-flight mass spectrometry and neutral detection via resonance enhance multiphoton ionization. The desorbing Ca could be fit using two Maxwell-Boltzmann components: a thermal component held at 600 K and a hyper-thermal component of 1389 K. Cross sections were found to be 1.1 (±0.7) × 10—20 cm2 and 3.2 (±0.9) × 10—24 cm2 for Ca and Ca+, respectively. Using these cross sections, a Monte Carlo model finds the neutral micro-exosphere produced by this process to be substantial. Lyman-α photon induced oxidation of ice covered carbon grains in photon dominated regions of proto-planetary disks have also been examined. CO and CO2 are formed at the buried ice:graphite interface via reaction of O and OH produced by direct photodissociation and dissociative electron attachment of interfacial water molecules. The non-thermal formation of CO and CO2 at the buried ice:grain interface may help regulate the carbon inventory during the early stage of planet formation. This may contribute to the carbon deficits in our solar system, and suggests that a universal carbon deficit gradient may be expected within astrophysical bodies surrounding center stars.

Photon-stimulated processes on planetary surfaces and in astrophysical environments

253rd National Meeting (2017)

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