Model organometallic systems. The interaction of 2S beryllium(1+) ion, 1S beryllium, and 3P beryllium atoms with acetylene and ethylene

Abstract

To model the interaction between metal atoms and unsaturated hydrocarbons, several electronic states of the Be-C/sub 2/H/sub 2/ and Be--C/sub 2/H/sub 4/ systems have been investigated using ab initio electronic structure theory. Double basis sets have been used (after some experimentation with polarization functions) at the self-consistent-field level of theory. For ten different electronic arrangements, potential energy curves have been predicted for the perpendicular approach of the Be nucleus to the midpoint of the carbon--carbon bond. The interaction of Be/sup +/ ion (ground /sup 2/S state) with both acetylene and ethylene is attractive, yielding equilibrium Be midpoint separations of 2.03 and 2.09 A and binding energies of 30 and 33 kcal/mole. In contrast the /sup 1/S ground state of the neutral Be atom has an essentially repulsive interaction. The threefold degenerate excited /sup 3/P state splits into /sup 3/A/sub 1/, /sup 3/B/sub 1/, and /sup 3/B/sub 2/ components as it approaches the ethylene molecule. The /sup 3/B/sub 2/ state is rather strongly bound, 19 kcal for Be--C/sub 2/H/sub 2/ and 25 kcal for Be-C/sub 2/H/sub 4/. the /sup 3/A/sub 1/ state is strongly repulsive, while the /sup 3/B/sub 1/ state assumes an intermediate role. These trends are readily explained bymore » qualitative molecular orbital concepts.« less