DFT calculations for anharmonic force field and spectroscopic constants of YC2 and its 13C isotopologues

B3PW91/QZ optimized geometry and Mayer bond order for YC2 confirm that the bonding of CC is double bond rather than intermediate between a double and triple bond. The complete third and the semi-diagonal quartic force fields and spectroscopic constants of YC2 and its 13C isotopologues are calculated.145