Which elements can be diatomic? Which elements can be diatomic and why?



Motivation

Hydrogen, Nitrogen, Oxygen and the Halogens tend to be thermodynamically stable as a diatomic molecule at room temperature, and are usually labelled as diatomic nonmetals. (Although I am unsure about Astatine). These are the ones you learn in school and I am fine with their reasoning. I want to know about other elements in particular.

Looking at the rest of the non-metals: Carbon, Phosphorus and Sulfur have diatomic molecules in gaseous states. All with a common theme of being heated at very high temperatures.

This leaves us with diatomic Selenium which I could not find anything on.



Further notes

Diatomicity doesn't seem to be just a non-metal thing:


Lithium forms diatomic molecules and all diatomic alkali metals are claimed to be stable in gaseous states. Found from this question.
Silicon has been reported to have a diatomic molecule similar in structure to carbon.
Tungsten, Chromium, Uranium and Molybdenum are claimed to be diatomic with a sextuple bond.
Supposedly Noble gases can form dimer molecules but if these are considered diatomic is debatable.
This leaves us with diatomic Selenium which I could not find anything on.


Selenium forms a dimer with bond energy of 79 kcal/mol, according to table 8.6 (page 451) of Comprehensive Handbook of Chemical Bond Energies, which provides 5 references.  

Tellenium dimer is 61 kcal/mol

Polonium dimer 45 kcal/mol