Electronic structure of excimer molecular lasers

The electronic structure, potential energy curves, and radiative transition probabilities of excimer systems have been examined using quantum mechanical methods. These molecules are characterized by repulsive or weakly bound ground state potential curves and by bound, strongly ionic, or Rydberg, excited states. They constitute a very interesting class of molecules which offer the possibility for high power, high efficiency UV laser operation. Calculations have been carried out using the density functional SCF -X_α method, modified extensively to correct for well known errors arising from approximations to the potential and exchange terms. A limited number of ab initio calculations were also carried out for comparison purposes. For the ArF system we find that the lowest excited ionic state has symmetry ²∑${}_{\text{½}}^{\text{+}}$ , and that the dominant laser transition observed at 1933 Å should be assigned to B ²∑${}_{\text{½}}^{\text{+}}$ → X ²∑${}_{\text{½}}^{\text{+}}$ . The C ²Π_3/2 → X ²∑${}_{\text{½}}^{\text{+}}$ transition is calculated to be two orders of magnitude smaller in emission intensity than the dominant transition, thus ruling out this assignment for the observed laser line in ArF. Preliminary calculations carried out for Ar₂F indicate that the bound upper ionic state has ²B₂ symmetry and that the most probable ground state also has ²B₂ symmetry. This polyatomic system is predicted to exhibit a broadband emission spectrum with a relatively long radiative lifetime.