Laser spectroscopy of holmium oxide: Examination of the low-lying electronic states

Abstract

Laser spectroscopic techniques have been used to examine the electronic, vibrational, rotational, and hyperfine structure of holmium oxide. Single-frequency, narrow-line (1 MHz), tunable cw dye lasers have been used to excite fluorescence in gas-phase HoO and resolved fluorescence and high-resolution excitation spectra have been obtained. Four low-lying and four higher-lying states have been observed. The energies and Ω assignments of all the states have been determined together with, in some cases, preliminary rotational constants and vibrational frequencies. The four low-lying states, including the Ω= 8.5 ground state, are shown, using ligand field theoretical arguments to result from ionically bonded Ho 2+O 2− in which the Ho 2+ configuration is 4 f 10( 5 I)6 s. The energy pattern and Ω assignments are shown to be in complete accord with ligand field theory predictions. Hyperfine structure, in some cases well resolved, has been observed in all high-resolution spectra and has been used to determine the free atomic ion quantum numbers for each low-lying state. The relative magnitudes of the hyperfine splitting in each of these states are used to estimate the relative contributions of the f and s electrons to the hyperfine structure.