Question

The degrees of freedom of a diatomic gas at normal temperature is

• A. 3
• B. 4
• C. 5
• D. 6

Answer 1

The correct option is C 5

In three-dimensional space, three degrees of freedom are associated with the movement of a particle. A diatomic gas molecule thus has 6 degrees of freedom. This set may be decomposed in terms of translations, rotations, and vibrations of the molecule. The center of mass motion of the entire molecule accounts for 3 degrees of freedom. In addition, the molecule has two rotational degrees of motion and one vibrational mode The rotations occur around the two axes perpendicular to the line between the two atoms. The rotation around the atom-atom bond is not a physical rotation. At normal temp, vibration is not possible. Hence, the total no of degrees of freedom is $f=3+2=5$