|Abstract:||The fundamental Ritz combination principle  originally found for atoms has also been applied to molecules as a method to reconstruct the energy states from measured lines without relying on any model Hamiltonian. In 2006 Nesbitt and coworkers  proposed to apply it to protonated methane, CH$_5^+$, which was first done in 2015  and extended in 2017  by our group. Currently, we are elaborating this method to a universal, easy to use tool which can be used for arbitrary spectra. Essentials of the program and examples, including the floppy He-H$_3^+$ system, will be discussed.
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 Oskar Asvany, Koichi M. T. Yamada, Sandra Brünken, Alexey Potapov, Stephan Schlemmer. Experimental ground-state combination differences of CH$_5^+$. Science, 347 (2015), pp. 1346-1349.\newline
 S. Brackertz, S. Schlemmer, O. Asvany, Searching for new symmetry species of CH$_5^+$ – From lines to states without a model, J. Mol. Spectrosc. 342 (2017), p. 73-82.\newline