TcX3+ and TcX3OH (X: O, S and Se) have been examined by vibrational (IR&Raman) spectroscopic study to see the isotopic mass effects on the spectra regarding the isotopes (O-16, O-17, O-18, S-32, S-33, S-34, S-36, Se-76, Se-78 and Se-80) employing the hybrid meta-GGA functional TPSSTPSS. The frequencies and intensities of the normal vibrational modes of the optimized molecules were used in explaining the mass effect of the isotopes. The calculated frequencies were mainly used in describing the isotopic mass effects by means of the potential energy distributions (PED). It was observed from the spectra that the vibrational frequencies and intensities of stretching and bending vibrations decreases with increasing atomic masses down the group of chalcogens (6 A) in the periodic table as expected. The same decreasing effect has been obtained with the increasing isotopic masses of O, S and Se atoms calculated in this study as well. There is no significant isotope effect on the frequencies of individual normal modes of the same element in the PED as the percent contribution to related vibrational motions. (C) 2018 Elsevier B.V. All rights reserved.