ANIKET NCERT

Different types of Energy :- 

Connecting macroscopic thermodynamics to a molecular understanding requires that we understand how energy is distributed on a molecular level.

ATOMS:-

The electrons: Electronic energy. Increase the energy of one (or more)electrons in the atom.

Nuclear motion: Translational energy. The atom can move around (translate) in space.

MOLECULES:-

The electrons: Electronic energy. Increase the energy of one (or more) electrons in the molecule.

Nuclear motion :-

1. Translational energy. The entire molecule can translate in space.
2. Vibrational energy. The nuclei can move relative to one another.
3.  Rotational energy. The entire molecule can rotate in space.

The lines are nearly equally spaced and vary in intensity.

We also will learn why the lines are nearly equally spaced and vary in intensity. Such

spectra can be used to determine bond lengths,and even bond angles in polyatomic molecules.

Absorption of Electromagnetic Radiation - The Coupling Mechanism :- 

An electromagnetic wave is an oscillating electrical field and interacts only with molecules that can undergo a change in dipole moment.

The oscillating dipole can be provided by the rotation of a permanent dipole like for example HCl. This type of interaction leads to microwave spectra

Microwave Spectroscopy :- 

Incident electromagnetic waves can excite the rotational levels of molecules provided they have an electric dipole moment. The electromagnetic field exerts a torque on the molecule.

The spectra for rotational transitions of molecules is typically in the microwave region of the electromagnetic spectrum.