quality:corruption
Spectroscopy

The reduced mass of the system in these equations is close to the mass of a single electron, but differs from it by a small amount about equal to the ratio of mass of the electron to the nucleus. For 1 H, this amount is about 1837 / 1836, or 1.000545, and for 2 H it is even smaller: 3671 / 3670, or 1.0002725. The energies of electronic spectra lines for 2 H and 1 H therefore differ by the ratio of these two numbers, which is 1.000272. The wavelengths of all deuterium spectroscopic lines are shorter than the corresponding lines of light hydrogen, by 0.0272%. In astronomical observation, this corresponds to a blue Doppler shift of 0.0272% of the speed of light, or 81.6 km/s.