For molecular and resonance spectroscopy

1. JAI NARAIN VYAS UNIVERSITY JODHPUR
Department of physics
2022-2023
Molecular and resonance spectroscopy
Topic:- electronic spectra
Presented by :- RAM NIWAS JAKHAR Submitted to:-Dr. S.L. MEENA

2. ELCTRONIC SPECTRA
It is a phenomenon of interaction of molecules with UV and visible lights.
It appears in the visible and ultraviolet region.
It involves a charge in all the three electronic , vibrational , rotational
energies of the molecules.
They are studied both in emission or absorption and the bands shows a fine
structure usually more complicated in vibrational – rotational bands.
All molecules exhibits electronic spectra. Homonuclear molecules such as 𝐻2 , 𝑁2,
𝑂2 𝑤ℎ𝑖𝑐ℎ 𝑛𝑒𝑖𝑡ℎ𝑒𝑟 𝑔𝑖𝑣𝑒 𝑟𝑜𝑡𝑎𝑡𝑖𝑜𝑛𝑎𝑙 𝑛𝑜𝑟 𝑟𝑜𝑡𝑎𝑡𝑖𝑜𝑛𝑎𝑙 𝑣𝑖𝑏𝑟𝑎𝑡𝑖𝑜𝑛𝑎𝑙 spectra exhibit
electronic spectra.

3. Formation of electronic spectra :-
 Let us consider the case of
diatomic molecules. If one
of its atoms is excited then
the molecules is said to be
excited. The various
possible electron
arrangements for a given
molecule from a pattern to
allowed electronic state for
the molecule.

4. Electronic transitions are not purely electronic the transition
involving both rotational and vibrational states.
Now the total energy is expressed in this term:-
𝐸𝑡𝑜𝑡𝑎𝑙 = 𝐸𝑒 + 𝐸𝑣 + 𝐸𝑟
𝐸𝑡𝑜𝑡𝑎𝑙 = 𝑉𝑒𝑙+ 𝑉
𝑒(𝑉 + 12)- 𝑋𝑒𝑉
𝑒(𝑉 + 12)12+BJ(J+1)-D 𝐽2(𝐽 + 1)2
Electronic vibrational rotational
rotational transition:-
rotational transition of molecules refers to
the abrupt change in the angular
momentum of that molecules.

5. Vibrational transition:- this transition of molecules
refers to the movement from one vibrational energy level to
another.
This type of transition occur in between different vibrational
level of the same electronic state.

6. The electronic spectra can be explained by Franck
Condon principle which state that electron
rearrangement occur so rapidly that nuclei can be
considered as stationary until the rearrangement is
complete