Topic 10: Ro-vibrational absorption spectroscopy

Part of module CH2PH1 at the University of Reading

[mariaph]

Hi professor Nutt,
Thank you for sharing the video. In 5:53, how do we know the one on the left is deltaJ=-1, and the one in the right is deltaJ=1?
I see similar graph from the Reilegh-raman scattering. But in that graph, the one on the left deltaJ=+2 instead of -2. I do not understand the sign difference. Could you please explain? Thank you so much.