High-resolution measurement of the electron affinity of cesium

Negative ions are unique quantum systems where electron correlation plays a decisive role in determining their properties. The lack of optically allowed transitions prevents traditional optical spectroscopy and the electron affinity is, therefore, for most elements, the only atomic quantity that can be determined with high accuracy. In this work, we present a high-precision experimental determination of the electron affinity of cesium. A collinear laser-ion beam apparatus was used to investigate the partial photodetachment cross section for the cesium anion, leaving the neutral atom in the <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:mrow><a:mn>6</a:mn><a:mi>p</a:mi></a:mrow><a:mo> </a:mo><a:mrow><a:msup><a:mrow/><a:mn>2</a:mn></a:msup><a:msub><a:mi mathvariant="italic">P</a:mi><a:mrow><a:mn>3</a:mn><a:mo>/</a:mo><a:mn>2</a:mn></a:mrow></a:msub></a:mrow></a:math> excited state. A resonance ionization scheme was used to obtain final-state selectivity, which enabled the investigation of a sharp onset of the cross section associated with a Wigner <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"><c:mrow><c:mi>s</c:mi></c:mrow></c:math>-wave threshold behavior. The electron affinity was determined to be <d:math xmlns:d="http://www.w3.org/1998/Math/MathML"><d:mrow><d:mn>0.471</d:mn><d:mspace width="0.16em"/><d:mn>598</d:mn><d:mspace width="0.16em"/><d:mn>3</d:mn><d:mo>(</d:mo><d:mn>38</d:mn><d:mo>)</d:mo><d:mspace width="0.16em"/><d:mi>eV</d:mi></d:mrow></d:math>.