Question

What is the basic difference between rotational, vibrational, rot-vibrational, and electronic spectra in spectroscopy?

Answer 1

These spectra depends on the energy of transition as

(1) rotational spectra occurs due to rotation of molecule which occurs due to microwaves

selection rule = permanent dipole moment in molecule

(2) vibrational spectra occurs due to vibration of molecule around pricipal axis but collectively called as rot - vib spe tra because when vibrational occurs always rotational (because at lower energy than vib) also occurs so called as rot - vibrational spectra occurs due to infrared waves having more enrgy than micriwaves

selection rule = change in dipole moment is requred or simply called polarisation

(3) electronic specra occurs when electron jump from one electronic level to another ,it occurs due to ultraviole radiations having more energy than even micro and infra so vibration and rotation always occurs in this.

selection rule = transition between symmetrical to unsymmetrical orbitals or vice versa only upto one level step b step

∆l = +-1

l = azimuthal quantam number