While hydrogen atoms in fundamental state emit both in cosmic spaces and in hydrogen maser a monochromatic radiation whose frequency 1.4204057 GHz is equal to the hyperfine splitting of their 1S spectral term, deuterium atoms do not emit a similar radiation with the frequency 0.327384 GHz equal to the hyperfine splitting of their 1S spectral term, neither in cosmic spaces (where huge quantities of deuterium exist), nor in hydrogen maser.
This different behavior is at least unexpected, as long as hydrogen and deuterium atoms have almost identical spectra, with very small differences between their homologous spectral lines because of the different reduced masses of the two atoms. More, the nuclear magnetic field in deuterium atoms is over four times weaker than in hydrogen atoms, which ought to favor an electron spin inversion similar to that causing 1.420406 GHz radiation mentioned above. For all that, such an electron spin inversion does not happen inside the nuclear magnetic field in deuterium atoms.
Is there an explanation for this absence of 0.327384 GHz radiation emitted by deuterium atoms?