Astronomy and Astrophysics – Astrophysics
Scientific paper
Nov 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011a%26a...535a..74b&link_type=abstract
Astronomy & Astrophysics, Volume 535, id.A74
Astronomy and Astrophysics
Astrophysics
Astrochemistry, Acceleration Of Particles, Molecular Processes
Scientific paper
A feasible initiation step for particle growth in the interstellar medium (ISM) is simulated by means of ab initio quantum chemistry methods. The systems studied are dimer ions formed by pairing nitrogen containing small molecules known to exist in the ISM with ions of unsaturated hydrocarbons or vice versa. Complexation energies, structures of ensuing complexes and electronic excitation spectra of the encounter complexes are estimated using various quantum chemistry methods. Møller-Plesset perturbation theory (MP2), Z-averaged perturbation theory (ZAPT2), coupled cluster singles and doubles with perturbative triples corrections (CCSD(T)), and density functional theory (DFT) methods (B3LYP) were employed along with the correlation consistent cc-pVTZ and aug-cc-pVTZ basis sets. Two types of complexes are predicted. One type of complex has electrostatic binding with moderate (7-20 kcal mol-1) binding energies, that are nonetheless significantly stronger than typical van der Waals interactions between molecules of this size. The other type of complex develops strong covalent bonds between the fragments. Cyclic isomers of the nitrogen containing complexes are produced very easily by ion-molecule reactions. Some of these complexes show intense ultraviolet-visible spectra for electronic transitions with large oscillator strengths at the B3LYP, ωB97, and equations of motion coupled cluster (EOM-CCSD) levels. The open shell nitrogen containing carbonaceous complexes especially exhibit a large oscillator strength electronic transition in the visible region of the electromagnetic spectrum.
Appendix A is available in electronic form at http://www.aanda.org
Bera Partha P.
Head-Gordon Martin
Lee Timothy J.
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