Question

Why don't atoms have vibrational and rotational states?

Answer 1

Well, mono-atomic molecules don’t quite exhibit rotational states since they’ve got nothin’ to rotate ’round, as apposed to poly-atomic atoms because an object that is perfectly symmetrical around some axis, it will be impossible for you to make it spin (nor, stop it) around that axis, because there is no microscopic handle for friction to push against.

And, mono-atomic molecules don’t exhibit vibration-al states since that one, constituent atom hasn’t got another atom in existence to bounce-off of and initiate a vibration-al motion,