Photodetachment Spectroscopy of Quasibound States of the Negative Ion of Lanthanum

TL;DR

This study used tunable infrared photodetachment spectroscopy to explore the complex quasibound states of La$^-$, revealing resonant peaks and thresholds that inform on its excited state structure and electron correlation effects.

Contribution

First detailed spectroscopic investigation of La$^-$ quasibound states using infrared photodetachment, highlighting complex resonance structures and state thresholds.

Findings

Observed 11 resonant peaks in photodetachment cross section.

Identified thresholds for detachment from multiple bound states.

Provided insights into multielectron correlation effects in La$^-$.

Abstract

The negative ion of lanthanum, La$^-$, has one of the richest bound state spectra observed for an atomic negative ion and has been proposed as a promising candidate for laser-cooling applications. In the present experiments, La$^-$ was investigated using tunable infrared photodetachment spectroscopy. The relative signal for neutral atom production was measured with a crossed ion-beam--laser-beam apparatus over the photon energy range 590 - 920 meV (2100 - 1350 nm) to probe the continuum region above the La neutral atom ground state. Eleven prominent peaks were observed in the La$^-$ photodetachment cross section due to resonant excitation of quasibound transient negative ion states in the continuum which subsequently autodetach. In addition, thresholds were observed for photodetachment from several bound states of La$^-$ to both ground and excited states of La. The present results provide information on the excited state structure and dynamics of La$^-$ that depend crucially on multielectron correlation effects.