| Summary: | Over a wide and partly overlapping energy range, the single-electron capture cross-sections for collisions of metastable <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msup><mi>Sn</mi><mrow><mn>2</mn><mo>+</mo></mrow></msup><mrow><mo>(</mo><mn>5</mn><mi>s</mi><mn>5</mn><mi>p</mi></mrow><mo> </mo><mmultiscripts><mi mathvariant="normal">P</mi><mi>o</mi><mn>3</mn></mmultiscripts><mo stretchy="false">)</mo></mrow></semantics></math></inline-formula> (<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msup><mi>Sn</mi><mrow><mn>2</mn><mo>+</mo><mo>∗</mo></mrow></msup></semantics></math></inline-formula>) ions with <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mi mathvariant="normal">H</mi><mn>2</mn></msub></semantics></math></inline-formula> molecules were measured (0.1–10 keV) and calculated (0.3–1000 keV). The semi-classical calculations use a close-coupling method on a basis of electronic wavefunctions of the (SnH<sub>2</sub>)<sup>2+</sup> system. The experimental cross-sections were extracted from double collisions in a crossed-beam experiment of <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msup><mi>Sn</mi><mrow><mn>3</mn><mo>+</mo></mrow></msup></semantics></math></inline-formula> with <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mi mathvariant="normal">H</mi><mn>2</mn></msub></semantics></math></inline-formula>. The measured capture cross-sections for <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msup><mi>Sn</mi><mrow><mn>2</mn><mo>+</mo><mo>∗</mo></mrow></msup></semantics></math></inline-formula> show good agreement with the calculations between 2 and 10 keV, but increase toward lower energies, whereas the calculations decrease. Additional Landau–Zener calculations were performed and show that the inclusion of spin-orbit splitting cannot explain the large cross-sections at the lowest energies which we now assume to be likely due to vibrational effects in the molecular hydrogen target.
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