Merged-Beams Study of the Reaction of Cold HD+ with C Atoms Reveals a Pronounced Intramolecular Kinetic Isotope Effect

We present a merged-beams study of reactions between <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mrow><a:msup><a:mrow><a:mi>HD</a:mi></a:mrow><a:mrow><a:mo>+</a:mo></a:mrow></a:msup></a:mrow></a:math> ions, stored in the Cryogenic Storage Ring (CSR), and laser-produced ground-term C atoms. The molecular ions are stored for up to 20 s in the extreme vacuum of the CSR, where they have time to relax radiatively until they reach their vibrational ground state (within 0.5 s of storage) and rotational states with <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"><c:mrow><c:mi>J</c:mi><c:mo>≤</c:mo><c:mn>3</c:mn></c:mrow></c:math> (after 5 s). We combine our experimental studies with quasiclassical trajectory calculations based on two reactive potential energy surfaces. In contrast to previous studies with internally excited <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"><e:mrow><e:msubsup><e:mrow><e:mi mathvariant="normal">H</e:mi></e:mrow><e:mrow><e:mn>2</e:mn></e:mrow><e:mrow><e:mo>+</e:mo></e:mrow></e:msubsup></e:mrow></e:math> and <h:math xmlns:h="http://www.w3.org/1998/Math/MathML" display="inline"><h:msubsup><h:mi mathvariant="normal">D</h:mi><h:mn>2</h:mn><h:mo>+</h:mo></h:msubsup></h:math> ions, our results reveal a pronounced isotope effect, favoring the production of <k:math xmlns:k="http://www.w3.org/1998/Math/MathML" display="inline"><k:mrow><k:msup><k:mrow><k:mi>CH</k:mi></k:mrow><k:mrow><k:mo>+</k:mo></k:mrow></k:msup></k:mrow></k:math> over <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" display="inline"><m:mrow><m:msup><m:mrow><m:mi>CD</m:mi></m:mrow><m:mrow><m:mo>+</m:mo></m:mrow></m:msup></m:mrow></m:math> across all collision energies, and a significant increase in the absolute rate coefficient of the reaction. Our experimental results agree well with our theoretical calculations for vibrationally relaxed <o:math xmlns:o="http://www.w3.org/1998/Math/MathML" display="inline"><o:mrow><o:msup><o:mrow><o:mi>HD</o:mi></o:mrow><o:mrow><o:mo>+</o:mo></o:mrow></o:msup></o:mrow></o:math> ions in their lowest rotational states. Published by the American Physical Society 2024