Please advice me some books or papers to understand the meaning of the sentence nuclear motions characterizing the vibrational coordinates?"
I guess that the nuclear motions are vibrational modes such as symmetrical stretching, bending, scissoring. Am I write?
[Moderator: Please be careful and don't post multiple times. One duplicate post deleted. I don't know what you mean when you write scissoring, but I think you are neglecting states with different angular momentum. ]