An update to the MARVEL data set and ExoMol line list for 12C2

Abstract

The spectrum of dicarbon (C2) is important in astrophysics and for spectroscopic studies of plasmas and flames. The C2 spectrum is characterized by many band systems with new ones still being actively identified; astronomical observations involve eight of these bands. Recently, Furtenbacher et al. (2016, Astrophys. J. Suppl., 224, 44) presented a set of 5699 empirical energy levels for 12C2, distributed among 11 electronic states and 98 vibronic bands, derived from 42 experimental studies and obtained using the Marvel (Measured Active Rotational-Vibrational Energy Levels) procedure. Here, we add data from 13 new sources and update data from 5 sources. Many of these data sources characterize high-lying electronic states, including the newly detected 3 3Πg state. Older studies have been included following improvements in the Marvel procedure which allow their uncertainties to be estimated. These older works in particular determine levels in the C 1Πg state, the upper state of the insufficiently characterized Deslandres–d’Azambuja (C 1Πg–A 1Πu) band. The new compilation considers a total of 31 323 transitions and derives 7047 empirical (Marvel) energy levels spanning 20 electronic and 142 vibronic states. These new empirical energy levels are used here to update the 8states C2 ExoMol line list. This updated line list is highly suitable for high-resolution cross-correlation studies in astronomical spectroscopy of, for example, exoplanets, as 99.4% of the transitions with intensities over 10−18 cm molecule−1 at 1000 K have frequencies determined by empirical energy levels.

The ExoMolOP database: Cross sections andk-tables for molecules of interest in high-temperature exoplanet atmospheres

“…These empirical energies are then subsequently included in the MARVELised Exo-Mol line lists to improve their accuracy (see, e.g. Chubb et al (2018Chubb et al ( , 2020bMcKemmish et al (2020)). As only a subsection of the energy levels, and therefore transitions, which are included in an ExoMol line list will have been MARVELised, the new ExoMol data format includes an uncertainty column in the .states file (Tennyson et al 2020).…”

A high-spectral-resolution catalog of emission lines in the visible spectrum of comet C/2020 F3 (NEOWISE)

“…Each time a coincidence occurred, we checked which emission was the most appropriate, analyzing from which energy level and emission band these lines originated. Finally, to further validate the final identification, we cross-checked our identification with those reported in other cometary spectral analyses (Cremonese et al 2007;Horne 1986;McKemmish et al 2020;Sneden et al 2014;Rousselot et al 2000;Picazzio et al 2002;Brown et al 1996b;Cochran & Cochran 2002).…”

Molecular diatomic spectroscopy data

“…Inclusion of new data in the full spectroscopic network of the molecule is also beneficial to the verification of the experimental data assignments; previous consolidations have led to the identification and correction of calibration errors (e.g. [56]), and could also be useful in speeding up new assignments (noting that of course previous data can be removed if the initial spectral assignments are rejected).…”

“…Where already compiled, new data should ideally be combined with the existing M arvel spectroscopic network, with existing line lists M arvel ized to incorporate the improved experimental data. Inclusion of new data in the full spectroscopic network of the molecule is also beneficial to the verification of the experimental data assignments; previous consolidations have led to the identification and correction of calibration errors, 53 and could also be useful in speeding up new assignments (noting that of course previous data can be removed if the initial spectral assignments are rejected).…”