Vibrations of a hydrogen molecule

[ZCML]

Homework Statement

Translated from swedish so i hope i get it right...

Observe vibrations along the axis of the bond in a hydrogen molecule (H2). For low temperatueres, by which factor does the rms value ("root-mean-square deviation") of these vibrations amplitude change if one of the hydrogen atoms is changed for a deuterium atom?

My problem is that i don't really know where to begin. So I am not asking for a solution (becasue i know you won't give me one) but a push in the right direction.

 

[Redbelly98]

At low temperatures, the hydrogen molecule will behave as a simple harmonic oscillator. Eg., 2 masses on a linear spring.