Petrie, Simon2015-12-132015-12-130004-9425http://hdl.handle.net/1885/87276High-level ab initio calculations are used to explore several aspects of calcium chemistry of direct relevance to formation and reaction of calcium-containing molecules in circumstellar envelopes. Counterpoise-corrected G2 and G2(MP2) calculations have been used to determine the bond dissociation energies (BDEs) of Ca+/NC2n+1H complexes (n = 0, 1, 2); these complexes, and CaNC7H+, are also assessed through counterpoise-corrected MP2(thaw)/6-3.11 + G(3df,2p) calculations. The relative energies of isomers of the feasible Ca(CN), Ca(C3N), and Ca(C5N) products (which may arise from dissociative recombination of the Ca+/NC2n+1H complexes) are obtained from G2 and G2(MP2) calculations; these calculations also permit evaluation of the thermochemistry of the dissociative recombination reactions in question. Thermochemical data are presented for a possible loss mechanism for calcium-containing neutrals by reaction with molecular ions in circumstellar envelopes. Finally, we provide an empirical assessment of the prospects for detecting the Ca(CN), Ca(C3N), and Ca(C5N) radicals within circumstellar environments.Keywords: Calculations; Chemical bonds; Chemistry; Dissociation; Isomers; Molecules; Positive ions; Quantum theory; Calcium cyanides; Circumstellar calcium chemistry; Dissociative recombination; Quantum chemical calculations; Calcium compounds200410.1071/CH031732015-12-12