Alkaline and alkaline-earth cyanoacetylides: A combined theoretical and rotational spectroscopic investigation

The metallic cyanoacetylides LiC₃N, NaC₃N, MgC₃N, and CaC₃N have been investigated by combined spectroscopy measurements and theoretical calculations. The theoretical calculations predict for the four species that the linear isomer with the formula MCCCN (M = Li, Na, Mg, and Ca) is the most stable one. We used laser ablation molecular beam Fourier transform microwave (FTMW) spectroscopy to synthesize these species by the reaction of metal vapors, produced by laser ablation, and 3-bromo-2-propynenitrile (BrCCCN). Pure rotational spectra were observed by FTMW spectroscopy in the 2-18 GHz frequency region only for LiCCCN and NaCCCN, while no spectral signatures for MgCCCN and CaCCCN could be detected. Finally, we have searched for LiCCCN and NaCCCN species toward the carbon-rich evolved star IRC +10 216, but only upper limits to their abundances have been obtained.