Impact of Nuclear Motion on Light-Induced Bimolecular Interaction Dynamics

In chemical reactions, the nuclear motion of the molecules plays a crucial role in determining the reaction rates and outcomes. Employing the cold target recoil ion momentum spectroscopy and femtosecond pump-probe techniques, we perform a molecular-level study into the influence of nuclear vibrations on light-induced bimolecular reactions within <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mrow><a:msub><a:mrow><a:mi mathvariant="normal">H</a:mi></a:mrow><a:mrow><a:mn>2</a:mn></a:mrow></a:msub><a:mtext>−</a:mtext><a:msub><a:mrow><a:mi mathvariant="normal">D</a:mi></a:mrow><a:mrow><a:mn>2</a:mn></a:mrow></a:msub></a:mrow></a:math> dimers. The study focuses on the formation dynamics of <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"><e:mrow><e:msub><e:mi mathvariant="normal">D</e:mi><e:mn>2</e:mn></e:msub><e:msup><e:mi mathvariant="normal">H</e:mi><e:mo>+</e:mo></e:msup></e:mrow></e:math> and <i:math xmlns:i="http://www.w3.org/1998/Math/MathML" display="inline"><i:mrow><i:msub><i:mi mathvariant="normal">H</i:mi><i:mn>2</i:mn></i:msub><i:msup><i:mi mathvariant="normal">D</i:mi><i:mo>+</i:mo></i:msup></i:mrow></i:math> cations, shedding light on the interplay between translational and vibrational motions of the nuclei steering the bimolecular reactions. Our observations reveal a notable yield ratio of <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" display="inline"><m:mrow><m:mn>1</m:mn><m:mo>:</m:mo><m:mn>1.6</m:mn></m:mrow></m:math> between <o:math xmlns:o="http://www.w3.org/1998/Math/MathML" display="inline"><o:mrow><o:msub><o:mi mathvariant="normal">H</o:mi><o:mn>2</o:mn></o:msub><o:msup><o:mi mathvariant="normal">D</o:mi><o:mo>+</o:mo></o:msup></o:mrow></o:math> and <s:math xmlns:s="http://www.w3.org/1998/Math/MathML" display="inline"><s:mrow><s:msub><s:mi mathvariant="normal">D</s:mi><s:mn>2</s:mn></s:msub><s:msup><s:mi mathvariant="normal">H</s:mi><s:mo>+</s:mo></s:msup></s:mrow></s:math> channels, accompanied with a faster formation of <w:math xmlns:w="http://www.w3.org/1998/Math/MathML" display="inline"><w:mrow><w:msub><w:mi mathvariant="normal">D</w:mi><w:mn>2</w:mn></w:msub><w:msup><w:mi mathvariant="normal">H</w:mi><w:mo>+</w:mo></w:msup></w:mrow></w:math> compared to <ab:math xmlns:ab="http://www.w3.org/1998/Math/MathML" display="inline"><ab:mrow><ab:msub><ab:mi mathvariant="normal">H</ab:mi><ab:mn>2</ab:mn></ab:msub><ab:msup><ab:mi mathvariant="normal">D</ab:mi><ab:mo>+</ab:mo></ab:msup></ab:mrow></ab:math>. Molecular dynamics simulations unveil that the faster vibrational motion of <eb:math xmlns:eb="http://www.w3.org/1998/Math/MathML" display="inline"><eb:mrow><eb:msubsup><eb:mrow><eb:mi mathvariant="normal">H</eb:mi></eb:mrow><eb:mrow><eb:mn>2</eb:mn></eb:mrow><eb:mrow><eb:mo>+</eb:mo></eb:mrow></eb:msubsup></eb:mrow></eb:math> than that of <hb:math xmlns:hb="http://www.w3.org/1998/Math/MathML" display="inline"><hb:mrow><hb:msubsup><hb:mrow><hb:mi mathvariant="normal">D</hb:mi></hb:mrow><hb:mrow><hb:mn>2</hb:mn></hb:mrow><hb:mrow><hb:mo>+</hb:mo></hb:mrow></hb:msubsup></hb:mrow></hb:math> upon single ionization within the dimer accounts for these differences. Our findings provide new insight into the time-resolved kinetic isotope effect on the bimolecular reactions, highlighting the critical relationship between nuclear vibrational motions and reaction dynamics. Published by the American Physical Society 2024