| Thinking out loud: When the universe was at 9000K, the vast majority of these elements did not exist or only existed at negligible concentration. Look up “Big Bang nucleosynthesis”. It would be interesting to see if the result is reproduced at all when looking at only light elements. Of course the bin width makes little difference. Bigger bins would just smooth the curve. There is probably a huge bias in that this looks at transitions that are interesting to the NIST database. As the authors allude, there are huge numbers of transitions that almost, but don’t quite, ionize at atom. Similarly, there are huge numbers of X-ray transitions in which inner electrons are kicked to very high levels or removed entirely. I don’t know to what extent the latter is well represented in the database. For that matter, there are transitions between bound states and unbound states. Imagine that you light up Hydrogen at 13.6 eV plus a little bit. I think you can still eject elections — the excess energy can be carried away as kinetic energy. (There can be issues with simultaneously conserving energy and momentum.). The unbound states are genuinely continuous. I didn’t look for real, but the NIST data has too many entries to represent just the spectra of cold atoms. I have a sneaking suspicion that researchers are measuring emissions from hot gasses or plasmas, perhaps heated near 9000K. |