Spectroscopic Parameters of HTiCN/HTiNC: New Titanium Compounds of Astrochemical Interest

A theoretical study of the [C, Ti, H, N] isomers, which are species of possible interstellar interest, has been carried out. We have employed different ab initio and density functional theory methodologies. Eleven isomers on the singlet, triplet, and quintet potential energy surfaces (PES) are characterized. The three most stable isomers of this system are obtained on the (3)A " PES from the interaction of the titanium atom of TiH with the cyano radical, CN, giving the open chains hydrotitanium cyanide/isocyanide (HTiCN/HTiNC) and the cyclic arrangement HTi-CN. For the most stable isomers we apply a composite approach that considers the extrapolation to the complete basis set limit, relativistic, and core-valence electron correlation corrections at the coupled-cluster level, including single and double excitations and a perturbative treatment of triple excitations (CCSD(T)). The lowest-lying isomer, HTiNC, is predicted to lie about 3.67 kcal mol(-1) and 3.86 kcal mol(-1) below HTiCN and the cyclic structure HTi-CN, respectively. The isomerization processes between these isomers shows that the cyclic structure could easily isomerize into HTiNC (the energy barrier is estimated to be only 0.48 kcal mol(-1)). We report harmonic and anharmonic frequencies, infrared intensities, and rotational constants that could help in their experimental characterization.