Origin of Molecular Oxygen in Comets: Current Knowledge and Perspectives.

The Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) instrument onboard the Rosetta spacecraft has measured molecular oxygen (O) in the coma of comet 67P/Churyumov-Gerasimenko (67P/C-G) in surprisingly high abundances. These measurements mark the first unequivocal detection of O in a cometary environment. The large relative abundance of O in 67P/C-G despite its high reactivity and low interstellar abundance poses a puzzle for its origin in comet 67P/C-G, and potentially other comets.

About the collapse of the 3.3 microm CH stretching band with ionization in polycyclic aromatic hydrocarbons: configuration interaction and quantum Monte Carlo studies of the CH fragment.

The puzzling difference between the IR spectra of polycyclic aromatic hydrocarbons (PAHs) and those of the corresponding positive ions (PAHs(+)) is a well documented fact, although the basic reason for it is far from clear. In this report, the CH fragment, in its neutral and ionized forms is taken as a case study for investigating the collapse of the CH stretching vibration with ionization. A comprehensive study of the dipole moment function around the equilibrium geometries of the fragments using large scale configuration interaction and quantum Monte Carlo methods shows very different variations with the CH distance: a marked decrease for neutral CH((2)Pi) and a perfect stability for ionized CH(+)((1)Sigma(+)).