Empirical rovibronic energy levels of C 3

The carbon trimer, C3 also known as propadienediylidene, is a quasi-linear molecule with an unusual electronic structure and a very flat bending potential in its ground electronic state. C3 is an important species in astrophysics and carbon plasmas. Observed transition wavenumbers within and between the X~1Σg+ and A~1Πu states of C3 are extracted from 21 papers and then subjected to a Measured Active Rotational-Vibrational Energy Levels (MARVEL) analysis: a corrected list of 4940 transitions are inverted to yield 1887 empirical energy levels. Uncertainties for these levels are determined using a newly implemented bootstrap method. These levels will provide input for developing a full spectroscopic model for C3 which can used to generate a line list for the X~1Σg+ and A~1Πu states.