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21 Cm Line.

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Posted by Alexander on February 20, 2001 18:36:40 UTC

Yes, it is specific spectroscopic notation labeling mutual orientation of spins of electron, proton and orbital moment (triplet and singlet).

Due to this splitting the energy level of main state of hydrogen 1s has 2 sublevels separated by 5.6 microelectronvolt, transition between which corresponds to absorbtion or radiation of a photon with the frequency 1.4204057517667 GHz or the wavelength 21.106114 cm.

Because the temperature of cold inerstellar hydrogen clouds is about T=3 K = 2.6x10-4 eV, thus no other transitions in Hydrogen atom can be exited by such small energy of thermal motion, but the 5.6 mmeV transition can and indeed seen brightly. Also, cold clouds absorb 21.1 cm radiation very good too.

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