1. The problem statement, all variables and given/known data I am wondering, is it possible to predict the vibrational frequency of D2 from H2, supposing vibrational frequency of H2 is 4400cm-1? 2. Relevant equations ... 3. The attempt at a solution From what I know, H2 has two H's, meaning 2 protons and 2 electrons, whereas D2 has 2 protons, 2 electrons AND 2 neutrons. So, is the mass the main factor here? If so, how do I 'predict' the vibrational frequency of D2? Will it be reduced to 1/2 or increased twice that of H2? Any hint would be appreciated!