Full spectroscopic model and trihybrid experimental-perturbative-variational line list for CN

Accurate line lists are important for the description of the spectroscopic nature of small molecules. While a line list for CN (an important molecule for chemistry and astrophysics) exists, no underlying energy spectroscopic model has been published, which is required to consider the sensitivity of transitions to a variation of the proton-to-electron mass ratio. Here we have developed a Duo energy spectroscopic model as well as a novel hybrid style line list for CN and its isotopologues, combining energy levels that are derived experimentally (Marvel), using the traditional/perturbative approach (Mollist), and the variational approach (from a Duo spectroscopic model using standard ExoMol methodology). The final Trihybrid ExoMol-style line list for ¹²C¹⁴N consists of 28 004 energy levels (6864 experimental, 1574 perturbative, the rest variational) and 2285 103 transitions up to 60 000 cm^-1 between the three lowest electronic states (X ²Σ⁺, A ²Π, and B ²Σ⁺). The spectroscopic model created is used to evaluate CN as a molecular probe to constrain the variation of the proton-to-electron mass ratio; no overly promising sensitive transitions for extragalactic study were identified.