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Ambient-light-induced intermolecular Coulombic decay in unbound pyridine monomers


Intermolecular Coulombic decay (ICD) is a process whereby photoexcited molecules relax by ionizing their neighbouring molecules. ICD is efficient when intermolecular interactions are active and consequently it is observed only in weakly bound systems, such as clusters and hydrogen-bonded systems. Here we report an efficient ICD between unbound molecules excited at ambient-light intensities. On the photoexcitation of gas-phase pyridine monomers, well below the ionization threshold and at low laser intensities, we detected the parent and heavier-than-parent cations. The isotropic emission of slow electrons revealed ICD as the underlying process. ππ* excitation in unbounded pyridine monomers triggered an associative interaction between them, which leads to an efficient three-centre ICD. The cation resulting from the molecular association of the three pyridine centres relaxed through fragmentation. This below-threshold ionization under ambient light has implications for the understanding of radiation damage and astrochemistry.

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Fig. 1: Time-of-flight mass spectrum (TOFMS) of the cations formed.
Fig. 2: VMI of the electrons ejected on ionization.
Fig. 3: Photoassociation of two pyridine molecules.
Fig. 4: ICD mechanisms that involve three photoexcited pyridine molecules and the eventual fragmentation of the trimer associate.
Fig. 5: Laser-power dependence of the parent cation yield.

Data availability

All the data supporting the findings of this study are available within the article and its Supplementary Information. Source data are provided with this paper.


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This work was supported by the Department of Science and Technology through project no. EMR/2016/005247 (G.A.) and the Indian Space Research Organisation through project no. ICSR/ISRO-IITM/PHY/16-17/173/GARA (G.A. and R.K.K.).

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Authors and Affiliations



S.B., G.A. and Y.S. conceived the three-centre ICD mechanism. S.B. and G.A. planned the experiment and carried out the measurements with the support of S.D., N.R.B. and R.K.K. Y.S. planned the quantum-chemistry calculations. The results were discussed among the authors. Y.S. and G.A. prepared the manuscript.

Corresponding authors

Correspondence to Y. Sajeev or G. Aravind.

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The authors declare no competing interests.

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Nature Chemistry thanks Xueguang Ren and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary information

Supplementary Information

Supplementary Figs. 1–8, Methods, Calculations and Computational Details.

Supplementary Data

Data used to generate figures in the Supplementary Materials file.

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Source Data Fig. 2

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Source Data Fig. 3

Data used to generate Figure 3.

Source Data Fig. 5

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Barik, S., Dutta, S., Behera, N.R. et al. Ambient-light-induced intermolecular Coulombic decay in unbound pyridine monomers. Nat. Chem. 14, 1098–1102 (2022).

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