Electronic states and nature of bonding in the molecule YC by all electron ab initio multiconfiguration self-consistent-field calculations and mass spectrometric equilibrium experiments

In the present work we present results of all electron ab initio multiconfiguration self-consistent-field calculations of eight electronic states of the molecule YC. Also reported are the calculated spectroscopic constants. The predicted electronic ground state is 4PI, but this state is found to be separated from a 2PI state by only 225 cm-1, and by 1393 cm-1 from a 2SIGMA+ state. The chemical bond in the 4PI ground state is mainly due to the formation of a bonding molecular orbital composed of the 4dpi of Y and the 2ppi on C. The 5s electrons of Y are partly transferred to the 2psigma orbital on C, and they hardly contribute to the bonding. The chemical bond in the YC molecule is polar with charge transfer from Y to C giving rise to a dipole moment of 3.90 D at 3.9 a.u. in the 4PI ground state. Mass spectrometric equilibrium investigations in the temperature range 2365-2792 K have resulted in the dissociation energy D0-degrees = 414.2 +/- 14 kJ mol-1 for YC(g), and a standard heat of formation DELTAH(f,298.15)-degrees = 708.1 +/- 16 kJ mol-1.