Calculated spectroscopic properties for C12H− and HC11N, molecules of astrochemical interest

A comparative theoretical study of the (potential) interstellar molecules C12H− and HC11N has been carried out, making use of the coupled cluster variant CCSD(T) in conjunction with large basis sets comprising up to 715 contracted Gaussian-type orbitals. The ground-state rotational constants of C12H− and C12D− are predicted to be 174.11 and 170.32 MHz, respectively. The corresponding quartic centrifugal distortion constant of C12H− is estimated to be 0.26 Hz, to be compared with an experimental value of 0.24 Hz for HC11N. Most of the total infrared intensity of C12H− isotopomers concentrates in one or two bands around 2000 cm−1. The total IR intensity exceeds 13 000 km mol−1 and is thus about 20 times larger than for HC11 N isotopomers. The bending vibrations of C12H−, HC11N and their deuterated species are analysed by means of mass plots.