Transition states and spin-orbit structure

doi:10.1126/science.abg3184

GSTDTAP > 气候变化

DOI	10.1126/science.abg3184
	Transition states and spin-orbit structure
	T. Peter Rakitzis
	2021-02-26
发表期刊	Science
出版年	2021
英文摘要	Transient intermediate structures between reactants and products in chemical reactions—transition states—can be probed by colliding the reactants at a well-defined collision energy E col, and then observing the product scattering angle θ and product kinetic and internal energy. By varying E col, sharp variations, or resonances, can be observed in the probability of forming the product at a particular scattering angle and internal energy. These resonances correspond to the energy-level structure of the transition state and have been investigated in the F + HD → HF + D reaction for decades ([ 1 ][1]). On page 936 of this issue, Chen et al. ([ 2 ][2]), through scattering experiments with high resolution and sensitivity, have observed a distinct set of scattering resonances for F + H, which theory can only reproduce by including electronic spin and orbital angular momentum. Thus, the authors measure the transition-state structure with previously unattainable sensitivity. The geometry and energetic structure of the transition region plays a crucial role in our understanding of chemical reactivity. However, the extremely short lifetime of the transition state (typically less than 10−12 s) does not allow the application of optical spectroscopy to probe its structure, so more indirect methods must be used. The energy of the electronic states of atoms and molecules is determined predominantly by the electrostatic attraction and repulsion among the negatively charged electrons and positively charged nuclei. Smaller but important contributions result from the magnetic interaction between the magnetic moments of the electron spins and the electronic orbital angular momentum, known as spin-orbit coupling. This coupling of the spin angular momentum s and the orbital angular momentum l yields the total angular momentum j , through vector addition, j = l + s . Thus, the quantum number j can have multiple values, ranging, in integer steps, from l + s when l and s are parallel to \| l − s \| when they are antiparallel. Each value of j corresponds to a different electronic state. For example, for halogen atoms (and H atoms in p orbitals), the quantum numbers l = 1 and s = 1/2 add to yield j = 3/2 (the halogen-atom ground state) and subtract to give state j = 1/2 (note that the quantized angular momentum magnitude ![Graphic][3], where ħ = h /2π, and h is Planck's constant). The relativistic spin-orbit energy splitting between these two states is very small for H(2p) atoms, at ∼0.000045 eV (where the average electron orbital speed is about 1% of the speed of light). However, it increases strongly with atomic number to reach 0.05 eV for F atoms and 0.94 eV for I atoms (where average electron orbital speed is a large fraction of the speed of light), and the spin-orbit energy is about 10% of the electron binding energy. Thus, spin-orbit effects play an increasingly important role for the structure and reactivity of heavy atoms. ![Figure][4] Explaining “horseshoe” scattering The reactive collision of F atoms and ground-state HD molecules to form HF + D studied by Chen et al. revealed scattering resonances that could only be explained by including spin-orbit energy effects. GRAPHIC: KELLIE HOLOSKI/ SCIENCE FROM T. P. RAKITZIS Until now, the theoretical treatments of the F + HD reaction needed to explain the extensive experimental measurements of the scattering distributions have not required the inclusion of spin-orbit effects in the transition state. Chen et al. selected a particular reactive resonance at a collision energy of 2.10 kcal/mol and identified a peculiar horseshoe-shaped feature in the scattering distribution (see the figure). This feature could not be well described by the standard theoretical treatment, which had errors of about 20 to 40% (red line in insets). However, when spin-orbit coupling is included ([ 3 ][5]), s and l are coupled to the nuclear orbital angular momentum L , to yield four states, with total angular momentum quantum numbers L ± 1/2 and L ± 3/2. The inclusion of the interference between these four spin-orbit split resonance pathways (J17.5L17−, J17.5L19−, J18.5L17+ and J18.5L19+) in the calculations provides the accurate dynamical picture of this benchmark chemical reaction (green line in insets). Through reactive scattering at a resonance, Chen et al. have identified a method for isolating and measuring the spin-orbit structure of the transition state. Given this result, it might seem that the impressive series of experiments on the F + HD reaction that test the theory of chemical reactions to new limits have reached their limit. For three-atom reactions, the end seems nearer than ever before. However, although the authors have controlled and measured the energy of the reactants and products with quantum-state precision, there is one final quantum number that is left to be controlled and measured: the magnetic quantum number mji of each angular momentum ji (where the subscript i can be F, HD, HF, or D), which is the projection of each ji on a laboratory axis and determines the relative spatial orientation of the angular momenta of the reactants and products. For example, selection of m j F can control whether the F-atom p orbital is preferentially parallel or perpendicular to the F velocity vector, and selection of m j HD (for j HD > 0) can control whether the HD bond is preferentially parallel or perpendicular to the HD velocity vector. Such control provides intuitive models of the reactive encounter, whereas the reduction in the averaging over all possible orientations will further amplify resonance effects and will test theory even more stringently. Methods for the control and measurement of the angular momentum orientation of HD, halogen atoms, HF, and D atoms have been demonstrated ([ 4 ][6]–[ 7 ][7]), opening the way for such m-state–resolved experiments. Progression to experiments with larger systems is also an obvious next step. Recently, theory explained the cold HCl rotational distributions from the nine-atom Cl + C2H6 → HCl + C2H5 reaction ([ 8 ][8]), resolving a nearly 25-year discrepancy with the experimental measurements. The close interplay between theory and experiment continues in the long quest to understand chemical reactivity and reactions of increasing complexity. 1. [↵][9]1. T. Wang et al ., Chem. Soc. Rev. 47, 6744 (2018). [OpenUrl][10][CrossRef][11][PubMed][12] 2. [↵][13]1. W. Chen et al ., Science 371, 936 (2021). [OpenUrl][14][Abstract/FREE Full Text][15] 3. [↵][16]1. Z. Sun, 2. D. H. Zhang, 3. M. H. Alexander , J. Chem. Phys. 132, 034308 (2010). [OpenUrl][17][CrossRef][18][PubMed][19] 4. [↵][20]1. N. C. M. Bartlett et al ., J. Chem. Phys. 129, 084312 (2008). [OpenUrl][21][PubMed][22] 5. 1. A. P. Clark, 2. M. Brouard, 3. F. Quadrini, 4. C. Vallance , Phys. Chem. Chem. Phys. 8, 5591 (2006). [OpenUrl][23][PubMed][24] 6. 1. A. Kvaran, 2. O. F. Sigurbjornsson, 3. H. S. Wang , J. Mol. Struct. 790, 27 (2006). [OpenUrl][25] 7. [↵][26]1. B. M. Broderick et al ., Rev. Sci. Instrum. 85, 053103 (2014). [OpenUrl][27] 8. [↵][28]1. D. Papp, 2. V. Tajti, 3. T. Győri, 4. G. Czakó , J. Phys. Chem. Lett. 11, 4762 (2020). [OpenUrl][29] Acknowledgments: We gratefully acknowledge X. Yang for providing the data for the figure and G. Katsoprinakis for assistance in its preparation. [1]: #ref-1 [2]: #ref-2 [3]: /embed/inline-graphic-1.gif [4]: pending:yes [5]: #ref-3 [6]: #ref-4 [7]: #ref-7 [8]: #ref-8 [9]: #xref-ref-1-1 "View reference 1 in text" [10]: {openurl}?query=rft.jtitle%253DChem.%2BSoc.%2BRev.%26rft.volume%253D47%26rft.spage%253D6744%26rft_id%253Dinfo%253Adoi%252F10.1039%252FC8CS00041G%26rft_id%253Dinfo%253Apmid%252F29955737%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [11]: /lookup/external-ref?access_num=10.1039/C8CS00041G&link_type=DOI [12]: /lookup/external-ref?access_num=29955737&link_type=MED&atom=%2Fsci%2F371%2F6532%2F886.atom [13]: #xref-ref-2-1 "View reference 2 in text" [14]: {openurl}?query=rft.jtitle%253DScience%26rft.stitle%253DScience%26rft.aulast%253DChen%26rft.auinit1%253DW.%26rft.volume%253D371%26rft.issue%253D6532%26rft.spage%253D936%26rft.epage%253D940%26rft.atitle%253DQuantum%2Binterference%2Bbetween%2Bspin-orbit%2Bsplit%2Bpartial%2Bwaves%2Bin%2Bthe%2BF%2B%252B%2BHD%2B-%253E%2BHF%2B%252B%2BD%2Breaction%26rft_id%253Dinfo%253Adoi%252F10.1126%252Fscience.abf4205%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [15]: /lookup/ijlink/YTozOntzOjQ6InBhdGgiO3M6MTQ6Ii9sb29rdXAvaWpsaW5rIjtzOjU6InF1ZXJ5IjthOjQ6e3M6ODoibGlua1R5cGUiO3M6NDoiQUJTVCI7czoxMToiam91cm5hbENvZGUiO3M6Mzoic2NpIjtzOjU6InJlc2lkIjtzOjEyOiIzNzEvNjUzMi85MzYiO3M6NDoiYXRvbSI7czoyMjoiL3NjaS8zNzEvNjUzMi84ODYuYXRvbSI7fXM6ODoiZnJhZ21lbnQiO3M6MDoiIjt9 [16]: #xref-ref-3-1 "View reference 3 in text" [17]: {openurl}?query=rft.jtitle%253DThe%2BJournal%2Bof%2BChemical%2BPhysics%26rft.stitle%253DThe%2BJournal%2Bof%2BChemical%2BPhysics%26rft.aulast%253DSun%26rft.auinit1%253DZ.%26rft.volume%253D132%26rft.issue%253D3%26rft.spage%253D034308%26rft.epage%253D034308%26rft.atitle%253DTime-dependent%2Bwavepacket%2Binvestigation%2Bof%2Bstate-to-state%2Breactive%2Bscattering%2Bof%2BCl%2Bwith%2Bpara-H%25282%2529%2Bincluding%2Bthe%2Bopen-shell%2Bcharacter%2Bof%2Bthe%2BCl%2Batom.%26rft_id%253Dinfo%253Adoi%252F10.1063%252F1.3290946%26rft_id%253Dinfo%253Apmid%252F20095740%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [18]: /lookup/external-ref?access_num=10.1063/1.3290946&link_type=DOI [19]: /lookup/external-ref?access_num=20095740&link_type=MED&atom=%2Fsci%2F371%2F6532%2F886.atom [20]: #xref-ref-4-1 "View reference 4 in text" [21]: {openurl}?query=rft.jtitle%253DThe%2BJournal%2Bof%2BChemical%2BPhysics%26rft.stitle%253DThe%2BJournal%2Bof%2BChemical%2BPhysics%26rft.aulast%253DBartlett%26rft.auinit1%253DN.%2BC.%26rft.volume%253D129%26rft.issue%253D8%26rft.spage%253D084312%26rft.epage%253D084312%26rft.atitle%253DPreparation%2Bof%2Boriented%2Band%2Baligned%2BH%25282%2529%2Band%2BHD%2Bby%2Bstimulated%2BRaman%2Bpumping.%26rft_id%253Dinfo%253Apmid%252F19044828%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [22]: /lookup/external-ref?access_num=19044828&link_type=MED&atom=%2Fsci%2F371%2F6532%2F886.atom [23]: {openurl}?query=rft.stitle%253DPhys%2BChem%2BChem%2BPhys%26rft.aulast%253DClark%26rft.auinit1%253DA.%2BP.%26rft.volume%253D8%26rft.issue%253D48%26rft.spage%253D5591%26rft.epage%253D5610%26rft.atitle%253DAtomic%2Bpolarization%2Bin%2Bthe%2Bphotodissociation%2Bof%2Bdiatomic%2Bmolecules.%26rft_id%253Dinfo%253Apmid%252F17149481%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [24]: /lookup/external-ref?access_num=17149481&link_type=MED&atom=%2Fsci%2F371%2F6532%2F886.atom [25]: {openurl}?query=rft.jtitle%253DJ.%2BMol.%2BStruct.%26rft.volume%253D790%26rft.spage%253D27%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [26]: #xref-ref-7-1 "View reference 7 in text" [27]: {openurl}?query=rft.jtitle%253DRev.%2BSci.%2BInstrum.%26rft.volume%253D85%26rft.spage%253D053103%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [28]: #xref-ref-8-1 "View reference 8 in text" [29]: {openurl}?query=rft.jtitle%253DJ.%2BPhys.%2BChem.%2BLett.%26rft.volume%253D11%26rft.spage%253D4762%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx
领域	气候变化 ; 资源环境
URL	查看原文
引用统计
文献类型	期刊论文
条目标识符	http://119.78.100.173/C666/handle/2XK7JSWQ/315925
专题	气候变化资源环境科学
推荐引用方式 GB/T 7714	T. Peter Rakitzis. Transition states and spin-orbit structure[J]. Science,2021.
APA	T. Peter Rakitzis.(2021).Transition states and spin-orbit structure.Science.
MLA	T. Peter Rakitzis."Transition states and spin-orbit structure".Science (2021).