The atoms dissociated from desorbed molecules occupy a large fraction of theneutrals in edge plasmas. Experiments of Balmer line emission, both in ourlinear device MAP [1] and in TEXTOR [2], show a group of atoms at very lowenergy (<1 eV). This paper evaluates the energy distributions ofdissociated atoms of the most important reaction channels of H2. Itis shown that the vibrational excitation can lead to a broad range energydistribution for the H2 dissociated into ground state atoms. However,the contribution to the dissociated atoms at energies below 0.5 eV, is not sosignificant. The photon emission rate starting from H(2s) excitation iscalculated and implemented in the DEGAS 2 modelling for our experiment case.From Hα modelling via DEGAS 2, it is concluded that the reactionchannel, H2 + e→ H2(1s σ, nlλ|1Λ)→ e + H (1s) + H (2s), andespecially one of the dissociated products H(2s) may be the main sourcecontributing to the Balmer line emissions where the low-energy component wasobserved.