Rotational vibrational spectra of diatomic molecules and selection rules
The radiation energy absorbed in IR region brings about the simultaneous change in the rotational and vibrational energies of the molecule. The spectrum obtained by these transitions is called vibrational rotational spectrum. The rotational vibrational energy is simply the sum of the separate energies. E total = E rot + E vib joule ε total = ε rot + ε vib cm -1 -(1) ε total = BJ ( J +1) + (ν + ½) ϖ e - x e ( ν + ½)² ϖ e -(2) The selection rules for the combined motions are the same as those for each seperately, therefore we have ∆ ν = ±1,±2, etc. ∆J = ±1 –(3) The vibrational change must be accomplished by a simultaneous rotational change. In fig 6 we have drawn some of the relevant energy levels and transition, designating rotational quantum numbers in the ν = 0 state as J” and in the ν = 1 state as J’. The use of a single prime for the upper state and a double for the lower state is conventional in all branches of spectroscopy.
#LearningScience
#Vibrationalrotationalspectra
#Infraredspectra
#Spectroscopy
#Selectionrule
