The microwave spectrum of a molecule yields three rotational constants. The molecule is:a)Prolate symmetric top.b)Spherical top.c)Asymmetric top.d)Oblate symmetric top.Correct answer is option 'C'. Can you explain this answer?

Question

Answer

Explanation:

Rotational constants are important in the study of molecular spectroscopy. They are used to determine molecular structures, as well as the moments of inertia of molecules. The moments of inertia dictate the rotational energy of a molecule, and thus the rotational spectrum.

The rotational constants of a molecule can provide information about its shape. Specifically, the rotational constants can be used to determine the shape of a molecule as a symmetric or asymmetric top.

- Symmetric Top Molecules:
Symmetric top molecules have two equal rotational constants. They have a rotational symmetry axis that passes through the center of mass. They are either prolate or oblate. In prolate symmetric top molecules, the axis of symmetry is the principal axis of rotation, while in oblate symmetric top molecules, the axis of symmetry is perpendicular to the principal axis of rotation.

- Asymmetric Top Molecules:
Asymmetric top molecules have three different rotational constants. They do not have a unique rotational axis. These molecules are not symmetric and have no planes of symmetry. They have a complex shape and are usually large and complex.

- Spherical Top Molecules:
Spherical top molecules have three equal rotational constants. They have a high degree of symmetry and are spherical in shape.

Therefore, in this question, the molecule has three different rotational constants, which means it is an asymmetric top molecule. Hence, option 'C' is the correct answer.

Answer

Separations of rotational energy levels correspond to the microwave region of the electromagnetic spectrum. In order for a molecule to absorb microwave radiation, it must have a permanent dipole moment. i.e. μ ≠ 0. This condition is known as the gross selection rule for microwave, or pure rotational, spectroscopy.

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