Hydroaluminum Isocyanide Isomers: Prediction of Spectroscopic Properties

Abstract

Metal cyanides and isocyanides play a relevant role in the metal chemistry of the carbon rich circumstellar envelope IRC+10216. It is thought that hydrometal cyanides/isocyanides could also be present in these environments; in fact, HMgNC has been detected in the same source that MgCN, MgNC, and AlNC. The aim of this work is to provide information about hydroaluminum cyanide/isocyanide. For this goal, a comprehensive analysis of the doublet and quartet potential energy surfaces of the [Al, C, H, N] system has been carried out. Different quantum chemistry methodologies from density functional theory to ab initio have been employed. For the [Al, C, H, N] isomers, the stability against dissociation and their interconversion processes have been analyzed. Our results show that the most relevant isomers from an experimental point of view are HAlCN and HAlNC. HAlNC has been found to be the most stable isomer followed by HAlCN, which is located at 1.59 kcal mol−1 (0.0689 eV) at the composite level. The interconversion process between HAlCN and HAlNC presents an energy barrier of 10.0 kcal mol−1 (5032 K) that makes this process not viable in the interstellar medium. We provide a complete set of relevant spectroscopic parameters for rotational spectroscopy for both HAlCN and HAlNC isomers using state-of-the-art quantum chemical computations, mandatory to guide an eventual laboratory or interstellar detection. Moreover, both isomers present sizable μa dipole moment components (3.7 and 3.3 D, respectively), which are large enough to enable a characterization by means of rotational spectroscopy, further increasing their interest as interstellar candidates.