Electron-attachment rates for carbon-rich molecules in protoplanetary atmospheres: the role of chemical differences

The formation of anionic species in the interstellar medium from interaction of linear molecules containing carbon, nitrogen and hydrogen as atomic components (polyynes) with free electrons in the environment is modelled via a quantum treatment of the collision dynamics. The ensuing integral cross sections are employed to obtain the corresponding attachment rates over a broad range of temperatures for the electrons. The calculations unequivocally show that a parametrization form often employed for such rates yields a broad range of values that turn out to be specific for each molecular species considered, thus excluding using a unique set for the whole class of polyynes.Comment: accepted to be published on MNRA

Neutral and ionic dopants in helium clusters: interaction forces for the Li2(a3Σu+)−HeLi_2(a^3\Sigma_u^+)-He and Li2+(X2Σg+)−HeLi_2^+(X^2\Sigma_g^+)-He

The potential energy surface (PES) describing the interactions between $\mathrm{Li_{2}(^{1}\Sigma_{u}^{+})}$ and $\mathrm{^{4}He}$ and an extensive study of the energies and structures of a set of small clusters, $\mathrm{Li_{2}(He)_{n}}$, have been presented by us in a previous series of publications [1-3]. In the present work we want to extend the same analysis to the case of the excited $\mathrm{Li_{2}}(a^{3}\Sigma_{u}^{+})$ and of the ionized Li$_{2}^{+}(X^{2}\Sigma_{g}^{+})$ moiety. We thus show here calculated interaction potentials for the two title systems and the corresponding fitting of the computed points. For both surfaces the MP4 method with cc-pV5Z basis sets has been used to generate an extensive range of radial/angular coordinates of the two dimensional PES's which describe rigid rotor molecular dopants interacting with one He partner

reply to comment on dynamics of formation of anthracene anions in molecular clouds and protoplanetary atmospheres

We discuss in some detail the implications of the suggestion made by P D Burrow and G A Gallup on the physics of anion formation and of resonant electron attachment in gas-phase anthracene molecules

ELECTRON-DRIVEN REACTIONS IN PROTO-PLANETARY ATMOSPHERES: METASTABLE ANIONS OF GASEOUS o-BENZYNE

In this paper, we present an investigation into low-energy electron scattering (E < 15 eV) processes from a specific benzene-like polyatomic target such as ortho-benzyne, o-C6H4(1?), in order to gain a better understanding of the effects that possible low-lying metastable electron-attachment states could have on its nuclear fragmentation dynamics. The current importance of the dynamical evolution of this molecule lies in the fact that o-C6H4 is considered to be relevant for the circumstellar synthesis of large polycyclic aromatic hydrocarbons (PAHs), as a precursor for C6H6 production via ion-based ring closure reaction from C2H2. Our parameter-free scattering calculations are performed within the molecular reference frame, where we obtain the metastable anionic states for the nuclear equilibrium configuration and further characterize the properties of such transient anions with respect to those found earlier for the benzene molecule. Our quantum studies indicate that o-C6H4 is a more efficient producer of compact, fairly long-lived anionic intermediates than benzene itself; hence, this should more rapidly enter the chemical reaction cycles of PAHs formation, thereby disappearing from possible direct observation as a stable anion