Diyttrium: Evidence for a ⁵Σ^-_u ground state from pulsed-field ionization-zero electron kinetic energy photoelectron spectroscopy and density functional calculations

Diyttrium has been studied by one-photon pulsed-field ionization-zero electron kinetic energy (PFI-ZEKE) photoelectron spectroscopy and density functional calculations. A spectrum consisting of 14 vibronic bands has been recorded at a resolution of ca. 0.5 cm^-1 in the 39 880-40 840 cm^-1 region. This spectrum is consistent with a X⁴Σ^-_g-X⁵Σ ^-_u transition, in accord with the results of density functional calculations and earlier ab initio calculations. Both states suffer from extensive second - order spin-orbit interactions which produce a splitting of 210 cm^-1 in the X⁴Σ^-_g state and 68 cm^-1 between the Ω = 2 and Ω = 0 spin-orbit components of the X⁵Σ^-_u state. These splittings serve to locate the perturbing ²Σ⁺_g and ³Σ⁺_u states. The ionization potential, measured by the X⁴Σ^-_1/2,g-X⁵Σ ^-_0,u (0,0) band, is determined to be 40 131(2) cm^-1. The vibrational frequencies have been determined to be 197(2) cm^-1 for the X⁴Σ^-_g state and 185(2) cm^-1 for the X⁵Σ^-_u state. The results of density functional calculations using the Amsterdam density functional (ADF) and GAUSSIAN92 codes are compared with experimental data and earlier ab initio results.