DIYTTRIUM - EVIDENCE FOR A (5)SIGMA(-)(U) GROUND-STATE FROM PULSED-FIELD IONIZATION-ZERO ELECTRON KINETIC-ENERGY PHOTOELECTRON-SPECTROSCOPYAND DENSITY-FUNCTIONAL CALCULATIONS

Diyttrium has been studied by one-photon pulsed-field ionization-zero electron kinetic energy (PFI-ZEKE) photoelectron spectroscopy and dens ity functional calculations. A spectrum consisting of 14 vibronic band s has been recorded at a resolution of ca. 0.5 cm(-1) in the 39880-408 40 cm(-1) region. This spectrum is consistent with a X(4) Sigma(g)(-)X (5) Sigma(u)(-) transition, in accord with the results of density func tional calculations and earlier ab initio calculations. Both states su ffer from extensive second - order spin-orbit interactions which produ ce a splitting of 210 cm(-1) in the X(4) Sigma(g)(-) State and 68 cm(- 1) between the Omega=2 and Omega=0 spin-orbit components of the X(5) S igma(u)(-) state. These splittings serve to locate the perturbing (2) Sigma(g)(+) and 3 Sigma(u)(+) states. The ionization potential, measur ed by the X(4) Sigma(1/2g)-X(5) Sigma(0,u)(-) (0,0) band, is determine d to be 40131(2) cm(-1). The vibrational frequencies have been determi ned to be 197(2) cm for the X(4) Sigma(g)(-) state and 185(2) cm(-1) f or the X(5) Sigma(u)(-) state. The results of density functional calcu lations using the Amsterdam density functional (ADF) and GAUSSIAN92 co des are compared with experimental data and earlier ab initio results.