An ab initio investigation of HC 4NC and C 5NH: two candidate molecules for interstellar detection

Abstract

Ab initio MP2/4-31G ∗∗ calculations have been performed to determine the molecular structures and dipole moments of HC 4NC and C 5NH. These molecules are found to be less stable than their isomer, HC 5N. HC 4NC is less stable by 34.2 kcal mol −1 and has a linear structure with a dipole moment of 3.43 D. C 5NH is bent (‘quasi-linear’) and has a dipole moment of 8.35 D. This quasi-linear structure is slightly more stable than its linear counterpart by 1.36 kcal mol −1 The energy difference between the C 5NH isomer and HC 5N is calculated to be 70.7 kcal mol −1. The B 0 rotational constants of HC 4NC and C 5NH have been estimated using a scaling procedure based on MP2/4-31G ∗∗ calculations performed on a group of similar molecules already identified in the interstellar medium. The estimated B 0 values for HC 4NC and C 5NH are 1400 ± 7 MHz and 1363 ± 7 MHz, respectively.