In rotational-vibrational spectroscopy P-branch corresponds to low level rotational transitions "delta J = -1" and R-branch to high rotations "delta J = +1". And I am confused about Q branch which corresponds to "delta J = 0" ; which means that no rotational change is there and it is allowed in some cases. I want to know when it is allowed and how?. Because when vibrational or electronic transitions are there rotational quantum number should change.(adsbygoogle = window.adsbygoogle || []).push({});

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# P,Q and R branches!

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