Empirical rovibrational energy levels for methane

A MARVEL (Measured Active Rotational Vibrational Energy Levels) analysis of the available spectroscopic data on methane (12C1H4) is performed. A total of 82173 measured rovibrational transitions were gathered from 96 literature sources and put through the MARVEL procedure which led to the determination of 23292 empirical energy levels with uncertainties, up to 9900 cm-1 covering the lowest eight polyads. A comparison with Effective Hamiltonian evaluated levels, variational calculations by the TheoReTS project, and the MeCaSDa database is performed. The new levels generated will be used to improve the upcoming ExoMol MM line list.