I was reading statistical mechanics today and came across a line

For $\ce{O2}$ and $\ce{N2},$ we get half-spin, and that is why we get $σ = 2$ in their rotational partition equation.

I didn't understand it quite well! What does this line mean, actually? And how can I determine the spin of $\ce{O2}$ or $\ce{N2}?$

Secondly, how did they state that $σ = 2?$

Reference: Haque. Physical Chemistry 4, 8th ed.; Shams Publication, 2021; Vol. 1.

  • 5
    $\begingroup$ Generally, it may be good to quote a broader context and marking the confusing part. // Your own reasoning – based on searching, reading and thinking – is supposed to be present to avoid the question closure for lack of own explicit effort. $\endgroup$
    – Poutnik
    Commented Jul 13, 2021 at 8:58
  • 1
    $\begingroup$ Did you read the box only? Certainly the book introduce that before. $\endgroup$
    – Alchimista
    Commented Jul 13, 2021 at 9:39
  • $\begingroup$ @Alchimista, what box? $\endgroup$
    – Asm Saikat
    Commented Jul 13, 2021 at 9:45
  • 1
    $\begingroup$ Quoting more than one sentence would be helpful. But I'd guess that you're probably looking for something called nuclear spin statistics. $\endgroup$ Commented Jul 13, 2021 at 10:09


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