Ionization and protonation of MgC3: A theoretical study

Abstract

AbstractA theoretical study of the MgC3+ and MgC3H+ species has been carried out. Predictions for their geometries and vibrational frequencies have been made at both second‐order Møller–Plesset (MP2) and B3LYP levels, whereas electronic energies have been computed at G2 and coupled cluster single and double excitation model augmented with a noniterative triple excitation conection (CCSD(T)) levels. The predicted global minimum for MgC3+ is a rhombic structure (2A1 electronic state), whereas a T‐shaped structure and an open‐chain isomer lie about 10 and 12 kcal/mol, respectively, higher in energy. In the case of MgC3H+ the predicted global minimum is also a four‐membered ring obtained upon protonation of the most stable neutral isomer. Low ionization potentials and high proton affinities are generally obtained, especially for the most stable MgC3+ isomer. The estimated values at the CCSD(T) level for the predicted global minimum are 7.20 eV [ionization potential (IP)] and 256.5 kcal/mol [proton affinities (PA)]. Therefore, if present in the interstellar medium, MgC3 should be easily ionized and would react quite easily to give the protonated species. © 2002 John Wiley & Sons, Inc. Int J Quantum Chem, 2001