Transfer of a proton between H 2 and O 2

Source abstract

The proton affinities of hydrogen and oxygen are very similar. Therefore, it has been discussed that the proton transfer from the omnipresent H to molecular oxygen in the near thermoneutral reaction effectively binds the interstellar oxygen in O 2 H + . In this work, the proton transfer reaction has been investigated in a low-temperature 22-pole ion trap from almost room temperature (280 K) down to the lowest possible temperature limited by freeze out of oxygen gas (about 40 K at a low pressure). The Arrhenius behaviour of the rate coefficient for the forward reaction shows that it is subject to an activation energy of E A / k =113 K. Thus, the forward reaction can proceed only in higher temperature molecular clouds. Applying laser-induced reactions to the given reaction (in the backward direction), a preliminary search for spectroscopic signatures of O 2 H + in the infrared was unsuccessful, whereas the forward reaction has been successfully used to probe the population of the lowest ortho and para levels of H .