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The results of our second stage (1998-2018) of the detailed spectroscopy ofpeculiar supergiants identified with galactic infrared sources, performedmainly at the 6-meter BTA telescope are summarized. The main aspect of theprogram is a search for the evolutionary variations in the chemical compositionof stars, past the AGB stage and the TDU, as well as an analysis of spectralmanifestations of kinematic processes in their extended, often unstable,atmospheres and in the envelopes. The most significant result is detection ofthe s-process element excesses in seven single post-AGB stars, which confirmsthe theory of evolution of this type of stars. In three of these stars we forthe first time discovered the ejection of the s-process heavy metals to thecircumstellar envelopes. A lithium excess was found in the atmospheres of twopeculiar supergiants V2324 Cyg and V4334 Sgr. The results of investigation ofthe kinematical state of atmospheres and envelopes will clarify the equilibriumof matter produced by stars in the AGB and post-AGB stages and delivered to theinterstellar medium.

Spectroscopy of supergiants with infrared excess: results of 1998-2018