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Phys.org's How sulfur helped make Earth habitable before the rise of oxygen says

Mapping the bonds and vibrational modes of molecules containing sulfur isotopes is helping to shed light on the chemical reactions that took place in Earth's atmosphere during the Archean era, before the atmosphere became oxygenated about 2.5 billion years ago.

and

The sulfur in the Archean Earth's atmosphere was emitted by volcanic activity, and through a process called mass independent fractionation, sulfur's various isotopes... became enriched in a manner that does not correlate with their mass.

It links to Computational analysis of vibrational modes in tetra-sulfur using dimensionally reduced potential energy surface and says that this paper

...explores some of the molecular bonds of a sulfur-4 (S4) molecule, and how these bonds affect the vibrational modes of the molecule, which in turn may influence the mass independent fractionation process.

Question: If the formation of tetra-sulfur is expected to be an important aspect of atmospheric chemistry in Earth's past, why is there so little experimental information on this molecule? Is it profoundly difficult to make, or to measure? Pardon the simple language, but What is tetrasulfur like? Why is there so little experimental information about it?

Wikipedia says only:

Tetrasulfur, S4

S4 has been detected in the vapour phase, but it has not been well characterized. Diverse structures (e.g. chains, branched chains and rings) have been proposed.[citation needed] Theoretical calculations suggest that S4 adopts a cyclic structure.


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    $\begingroup$ While sulfur vapor might have been important (I'm afraid is a bit speculatory though) who says this form was? It was only "detected" in vapor, so it's much less important part of it then S3 or S2. It is somewhat interesting why it's marginal. $\endgroup$ – Mithoron Nov 7 '19 at 22:44
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    $\begingroup$ Not all good quality information is online. Please consult Elemental Sulfur and Sulfur-Rich Compounds I By Bodo Eckert. He almost has a chapter on this topic. $\endgroup$ – M. Farooq Nov 9 '19 at 3:17
  • $\begingroup$ @M.Farooq yes indeed, books! I'll find a copy this weekend. Thanks! $\endgroup$ – uhoh Nov 9 '19 at 3:38
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    $\begingroup$ Have a look at this paper: cfa.harvard.edu/mmw/mmwlab/websitepdf/113.pdf $\endgroup$ – Nilay Ghosh May 6 at 9:14
  • $\begingroup$ @NilayGhosh oh that's very cool, thank you! Figure 3 reminds me of my more recent question Does the nitrogen atom move with in the molecule in an ammonia maser, or does the molecule flip? $\endgroup$ – uhoh May 6 at 9:28

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