Doppler-free resonant Auger Raman spectroscopy on atoms and molecules at SPring-8

At the high resolution electron spectroscopy end station of BL27 at SPring-8 in Japan we replaced the conventional gas-cell with a Doppler free gas-jet source. Such a device was constructed in such a way that the gaseous molecules, or atoms, travel perpendicularly to the direction of observation of the electron energy analyzer, so that the Doppler broadening is removed. This apparatus has been tested and proved successfully for resonant Auger emission of Ne 1s^-1 3p and H₂O O 1s^-1 2b₂ and O 1s^-1 4a₁. In the experiment on Ne, electrons of about 811 eV of energy are observed with a width of 63 meV. Such narrow width allows to resolve terms of inner-valence excited states of the series Ne ⁺ 2s2p⁵(^1,3P)np ²S, ²P, ²D; and also to extract the natural lifetime widths of states that can undergo further Auger decay. This Doppler-free technique was also applied in H₂O, to study the Auger decay from the O 1s^-1 2b ₂ and O 1s^-1 4a₁ core-excited states. The Doppler-free system allows to resolve the vibrational structure in the final Auger state, thus to investigate details of nuclear dynamics in the core excited state.