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Intersystem crossing in the exit channel


Intersystem crossing plays an important role in photochemistry. It is understood to be efficient when heavy atoms are present due to strong spin–orbit coupling, or when strongly bound long-lived complexes are formed that increase the chance of finding the singlet–triplet intersection seam. Here we present evidence for a different intersystem crossing mechanism in the bimolecular reaction of O(3P) with alkylamines. In crossed-beam experiments, product velocity–flux maps are measured for aminoalkyl radicals produced from H abstraction from the methyl group, which also gives OH radicals as co-fragments. The low translational-energy release and isotropic angular distributions of the products indicate that such reactions undergo the formation of a complex before OH and aminoalkyl are produced. However, there is no well on the triplet potential energy surface that could support such a complex. Multi-reference ab initio calculations suggest, instead, that intersystem crossing occurs in the exit-channel region due to the long-range dipole–dipole interaction between the nascent radical product pair coupled with the vanishing singlet–triplet splitting at long range. Intersystem crossing then leads to a deep hydroxylamine well before OH elimination.

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Fig. 1: Velocity–flux contour map analysis of aminoalkyl products from reactions of O(3P) with DMA and TMA.
Fig. 2: Key points on the triplet and singlet PESs of the O(3P) + DMA reaction.
Fig. 3: Spin–orbit coupling and high level energy calculations.
Fig. 4: Orbitals participating in the wavefunctions of S0, S1, T1 and T2.
Fig. 5: Snapshots of a representative trajectory.

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The authors confirm that all relevant data are included in the paper and/or its Supplementary Information, except raw image data, which are available on reasonable request from the authors.


  1. Bolton, O., Lee, K., Kim, H. J., Lin, K. Y. & Kim, J. Activating efficient phosphorescence from purely organic materials by crystal design. Nat. Chem. 3, 205–210 (2011).

    Article  CAS  Google Scholar 

  2. Goushi, K., Yoshida, K., Sato, K. & Adachi, C. Organic light-emitting diodes employing efficient reverse intersystem crossing for triplet-to-singlet state conversion. Nat. Photon. 6, 253–258 (2012).

    Article  CAS  Google Scholar 

  3. Zhao, J. Z., Wu, W. H., Sun, J. F. & Guo, S. Triplet photosensitizers: from molecular design to applications. Chem. Soc. Rev. 42, 5323–5351 (2013).

    Article  CAS  Google Scholar 

  4. Kamkaew, A. et al. BODIPY dyes in photodynamic therapy. Chem. Soc. Rev. 42, 77–88 (2013).

    Article  CAS  Google Scholar 

  5. Koziar, J. C. & Cowan, D. O. Photochemical heavy-atom effects. Acc. Chem. Res. 11, 334–341 (1978).

    Article  CAS  Google Scholar 

  6. Alagia, M. et al. Crossed beam studies of the O(3P,1D) + CH3I reactions: direct evidence of intersystem crossing. Faraday Discuss. 113, 133–150 (1999).

    Article  CAS  Google Scholar 

  7. Casavecchia, P., Leonori, F. & Balucani, N. Reaction dynamics of oxygen atoms with unsaturated hydrocarbons from crossed molecular beam studies: primary products, branching ratios and role of intersystem crossing. Int. Rev. Phys. Chem. 34, 161–204 (2015).

    Article  CAS  Google Scholar 

  8. Fu, B. N. et al. Intersystem crossing and dynamics in O(3P) + C2H4 multichannel reaction: experiment validates theory. Proc. Natl Acad. Sci. USA 109, 9733–9738 (2012).

    Article  CAS  Google Scholar 

  9. Leonori, F. et al. Experimental and theoretical studies on the dynamics of the O(3P) + propene reaction: primary products, branching ratios and role of intersystem crossing. J. Phys. Chem. C 119, 14632–14652 (2015).

    Article  CAS  Google Scholar 

  10. Leonori, F. et al. Crossed molecular beam dynamics studies of the O(3P) + allene reaction: primary products, branching ratios and dominant role of intersystem crossing. J. Phys. Chem. Lett. 3, 75–80 (2012).

    Article  CAS  Google Scholar 

  11. Schmoltner, A. M., Chu, P. M., Brudzynski, R. J. & Lee, Y. T. Crossed molecular beam study of the reaction O(3P) + C2H4. J. Chem. Phys. 91, 6926–6936 (1989).

    Article  CAS  Google Scholar 

  12. Schmoltner, A. M., Huang, S. Y., Brudzynski, R. J., Chu, P. M. & Lee, Y. T. Crossed molecular-beam study of the reaction O(3P) + allene. J. Chem. Phys. 99, 1644–1653 (1993).

    Article  CAS  Google Scholar 

  13. Joalland, B. et al. Dynamics of chlorine atom reactions with hydrocarbons: insights from imaging the radical product in crossed beams. J. Phys. Chem. A 118, 9281–9295 (2014).

    Article  CAS  Google Scholar 

  14. Li, W., Chambreau, S. D., Lahanker, S. A. & Suits, A. G. Megapixel ion imaging with standard video. Rev. Sci. Instrum. 76, 063106 (2005).

    Article  Google Scholar 

  15. Montgomery, J. A., Frisch, M. J., Ochterski, J. W. & Petersson, G. A. A complete basis set model chemistry. VII. Use of the minimum population localization method. J. Chem. Phys. 112, 6532–6542 (2000).

    Article  CAS  Google Scholar 

  16. Frisch, M. J. et al. Gaussian 09 Revision D.01 (Gaussian, 2013).

  17. Joalland, B., Shi, Y., Kamasah, A., Suits, A. G. & Mebel, A. M. Roaming dynamics in radical addition-elimination reactions. Nat. Commun. 5, 4064 (2014).

    Article  CAS  Google Scholar 

  18. Slagle, I. R., Dudich, J. F. & Gutman, D. Identification of reactive routes in the reactions of oxygen atoms with methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine and triethylamine. J. Phys. Chem. 83, 3065–3070 (1979).

    Article  CAS  Google Scholar 

  19. Atkinson, R. & Pitts, J. N. Kinetics of the reactions of O(3P) atoms with the amines CH3NH2, C2H5NH2, (CH3)2NH, and (CH3)3N over the temperature range 298–440 °K. J. Chem. Phys. 68, 911–915 (1978).

    Article  CAS  Google Scholar 

  20. Balucani, N., Leonori, F., Casavecchia, P., Fu, B. N. & Bowman, J. M. Crossed molecular beams and quasiclassical trajectory surface hopping studies of the multichannel nonadiabatic O(3P) + ethylene reaction at high collision energy. J. Phys. Chem. A 119, 12498–12511 (2015).

    Article  CAS  Google Scholar 

  21. Schmidt, M. W. et al. General atomic and molecular electronic structure system. J. Comput. Chem. 14, 1347–1363 (1993).

    Article  CAS  Google Scholar 

  22. Gordon, M. S. & Schmidt, M. W. in Theory and Applications of Computational Chemistry: The First Forty Years (eds Dykstra, D. E., Frenking, K. S. K. & Scuseria, G. E.) 1167–1189 (Elsevier, Amsterdam, 2005).

  23. Nakano, H. Quasidegenerate perturbation theory with multiconfigurational self‐consistent‐field reference functions. J. Chem. Phys. 99, 7983–7992 (1993).

    Article  CAS  Google Scholar 

  24. Nakano, H. MCSCF reference quasidegenerate perturbation theory with Epstein–Nesbet partitioning. Chem. Phys. Lett. 207, 372–378 (1993).

    Article  CAS  Google Scholar 

  25. El‐Sayed, M. A. Spin–orbit coupling and the radiationless processes in nitrogen heterocyclics. J. Chem. Phys. 38, 2834–2838 (1963).

    Article  Google Scholar 

  26. Zobel, J. P., Nogueira, J. J. & González, L. Mechanism of ultrafast intersystem crossing in 2-nitronaphthalene. Chem. Eur. J. 24, 5379–5387 (2018).

    Article  CAS  Google Scholar 

  27. Ahmed, M., Peterka, D. S. & Suits, A. G. Imaging H abstraction dynamics in crossed molecular beams: Cl + ROH reactions. Phys. Chem. Chem. Phys. 2, 861–868 (2000).

    Article  CAS  Google Scholar 

  28. Huang, C., Li, W. & Suits, A. G. Rotationally resolved reactive scattering: imaging detailed Cl+C2H6 reaction dynamics. J. Chem. Phys. 125, 133107 (2006).

    Article  Google Scholar 

  29. Abeysekera, C. et al. Note: a short-pulse high-intensity molecular beam valve based on a piezoelectric stack actuator. Rev. Sci. Instrum. 85, 116107 (2014).

    Article  Google Scholar 

  30. Kawasaki, M. & Sato, H. Photodissociation of molecular beams of SO2 at 193 nm. Chem. Phys. Lett. 139, 585–588 (1987).

    Article  CAS  Google Scholar 

  31. Felder, P., Effenhauser, C. S., Haas, B. M. & Huber, J. R. Photodissociation of sulfur dioxide at 193 nm. Chem. Phys. Lett. 148, 417–422 (1988).

    Article  CAS  Google Scholar 

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The experimental research (A.G.S.) was supported by the Director, Office of Science, Office of Basic Energy Science, Division of Chemical Science, Geoscience and Bioscience of the US Department of Energy under contract no. DE-SC0017130 with additional support from the ARO under grant no. W911NF-17-1-0099. S.M. was supported by the NSF (CHE-1800171). The authors thank J. M. Bowman for comments on the manuscript and T. Sewell for helpful discussions.

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Authors and Affiliations



H.L. and A.K. performed the experiments and analysed the data. H.L. and S.M. performed the theoretical calculations and analysed the results. A.G.S. conceived the experiments and guided the interpretation. H.L., S.M. and A.G.S. co-wrote the paper. All authors discussed the results and commented on the manuscript.

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Correspondence to Arthur G. Suits.

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Supplementary information

Supplementary Information

Supplementary Results, Supplementary Figures 1 and 2, key stationary point geometries

Supplementary Movie

This video contains animations of one trajectory starting from the transition state of the direct H-abstraction process to OH + CH3NHCH2 products on the triplet surface, calculated using a Born–Oppenheimer molecular dynamics model at the B3LYP/6–31G(d) level of theory. Colour coding for atoms: carbon (grey), nitrogen (blue), oxygen (red) and hydrogen (white). A few snapshotsfor this trajectory are shown in Fig. 5.

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Li, H., Kamasah, A., Matsika, S. et al. Intersystem crossing in the exit channel. Nature Chem 11, 123–128 (2019).

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