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In this work we present the main atmospheric parameters, carbon, nitrogen andoxygen abundances, and 12C/13C ratios determined in a sample of 28 Galacticclump stars. Abundances of carbon were studied using the C2 band at 5086.2{\AA}. The wavelength interval 7980-8130 {\AA} with strong CN features wasanalysed in order to determine nitrogen abundances and 12C/13C isotope ratios.The oxygen abundances were determined from the [O I] line at 6300 {\AA}. Themean abundances of C, N and O abundances in the investigated clump starssupport our previous estimations that, compared to the Sun and dwarf stars ofthe Galactic disc, carbon is depleted by about 0.2 dex, nitrogen is enhanced by0.2 dex and oxygen is close to abundances in dwarfs. The 12C/13C and C/N ratiosfor galactic red clump stars analysed were compared to the evolutionary modelsof extra-mixing. The steeper drop of 12C/13C ratio in the model of thermohalinemixing by Charbonnel & Lagarde better reflects the observational data at lowstellar masses than the more shallow model of cool bottom processing byBoothroyd & Sackmann. For stars of about 2 Msun masses a modelling ofrotationally induced mixing should be considered with rotation of about 250 kms-1 at the time when a star was at the hydrogen-core-burning stage.

Red clump stars of the Milky Way - laboratories of extra-mixing