Exploring a dynamical path for C2H− and NCO− formation in dark molecular clouds

Abstract

This paper deals with the possible formation of two molecular anions often considered likely components in the physical environments of the Interstellar Medium ( ISM) : C 2 H − and NCO − . They are both discussed here by computationally following the radiative association (RA) mechanism starting from C − 2 , H, NC − and O as partners. The corresponding RA total cross sections produced by the calculations are in turn employed to generate the overall association rates over the relevant range of temperatures. The latter are found to be in line with other molecular ions formed by RA but not large enough to uniquivocally suggest this path as the main route to the anions formation in the ISM. Other possible paths of formation are also analysed and discussed.The presence of resonant structures during the association dynamics for both systems is found by the calculations and their consequences are discussed in some detail in the present study.

Negative Ions in Space

“…This was identified unambiguously as NCO – embedded in a strong hydrogen-bonded ice based on isotopic substitution experiments. The gas-phase formation of the anion through the radiative association CN – + O was shown to have an extremely small rate coefficient at low temperatures, less than 2.5 × 10 –19 cm 3 s –1 , and the direct radiative electron attachment to NCO is also very slow . Laboratory experiments indicate that the origin of the anion might be due to photon or cosmic-ray interaction with the ice, although it has also been argued that the anion can be produced by low-temperature thermal reactions between HNCO and NH 3 in ice …”

N2+(2Σg) and Rb(2S) in a hybrid trap: modeling ion losses from radiative association paths

“…We expect that this simple model can already provide us with valuable information on the relative importance of the two possible mechanisms mentioned earlier as dissipative paths leading to trap losses during the experimental process. 15 Once the relative collision energy, E, between partners is selected from the specific kinematic conditions in the trap, the RA cross section, involving a transition from a continuum initial state at angular momentum J to a discrete level ( J 0 ,v) of the upper (s = 1, vibrational process) or lower (s = 2, vibronic process) electronic state, is given, at each orientation (o = collinear or T-shaped) by: 26,27…”