Stability, metastability and spectroscopic properties of some low-lying electronic states of C2H−and N2H−

Abstract

Accurate ab initio calculations have been carried out and the potential energy surfaces (PESs) and the potential energy curves (PECs) of the lowest states of the neutral C2H and N2H and those of the electronic states of their respective negative ion C2H− and N2H− correlating to the bound asymptotes of these molecular systems determined. These calculations reveal that the ground states of C2H− and N2H− are respectively X1Σ+ and X1A′ and the long range parts of anionic PESs of C2H− and N2H− are stable against the autodetachment processes. In the light of these computations, we also predict some long lived excited states for all these anions. C2H− possesses a linear structure with a ground state located solely and does not interact strongly with other states. N2H− presents a bent structure. The b3A′ electronic state of this anion which equilibrium’s geometry is RNN=2.44 a0, RNH=1.97 a0 and θ=113.5 degree, reveals itself to be the most indicated state in which spectroscopic studies can be done and in which the anion can be described, thanks to its bound nature. The three-dimensional PES of this metastable state is generated using a coupled cluster approach associated with a large basis sets. A set of spectroscopic parameters for N2H− (b3A′) are deduced from a 3D PES. Finally, the 5A′ and 5A″ states that correlate at the linearity form a bent/bent Renner-Teller in the bent structure. The computed electron affinity of C2H is in very good agreement with the available experimental values.