Observation of the fine structure for rovibronic spectral lines in visible part of emission spectra of $D_2$

For the first time in visible part of the $D_2$ emission spectrum the pseudo doublets representing partly resolved fine structure of rovibronic lines have been observed. They are characterized by splitting values about 0.2 cm${}^{-1}$ and relative intensity of the doublet components close to 2.0. It is shown that they are determined by triplet splitting in lower rovibronic levels of various ${}^3{\mathrm{\Lambda }}_g^{\pm }\to c^3{\mathrm{\Pi }}_u^{-}$ electronic transitions. It is proposed to use an existence of such partly resolved fine structure patterns for identification of numerous unassigned spectral lines of the $D_2$ molecule coming from great variety of triplet “gerade” electronic states to vibro-rotational levels of the $c^3{\mathrm{\Pi }}_u^{-}$ state.