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.

Experimental energy levels of 12C14N through marvel analysis

The cyano radical (CN) is a key molecule across many different factions of astronomy and chemistry. Accurate, empirical rovibronic energy levels with uncertainties are determined for eight doublet states of CN using the marvel (Measured Active Rotational-Vibrational Energy Levels) algorithm. 40 333 transitions were validated from 22 different published sources to generate 8083 spin-rovibronic energy levels. The empirical energy levels obtained from the marvel analysis are compared to current energy levels from the mollist line list. The mollist transition frequencies are updated with marvel energy level data which brings the frequencies obtained through experimental data up to 77.3 per cent from the original 11.3 per cent, with 92.6 per cent of the transitions with intensities over 10-23 cm molecule-1 at 1000 K now known from experimental data. At 2000 K, 100.0 per cent of the partition function is recovered using only marvel energy levels, while 98.2 per cent is still recovered at 5000 K.

PhysChem 2019: RACI Australian Conference on Physical Chemistry, Perth, 11–14 February 2019

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