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Quantum dynamical resonances in low-energy CO(j = 0) + He inelastic collisions



In molecular collisions, long-lived complexes may be formed that correspond to quasi-bound states in the van der Waals potential and give rise to peaks in the collision energy-dependent cross-sections. They are known as ‘resonances’ and their experimental detection remains difficult because their signatures are extremely challenging to resolve. Here, we show a complete characterization of quantum-dynamical resonances occurring in CO–He inelastic collisions with rotational CO(j = 0  1) excitation. Crossed-beam scattering experiments were performed at collision energies as low as 4 cm−1, equivalent to a temperature of 4 K. Resonance structures in the measured cross-sections were identified by comparison with quantum-mechanical calculations. The excellent agreement found confirms that the potential energy surfaces describing the CO–He van der Waals interaction are perfectly suitable for calculating state-to-state (de)excitation rate coefficients at the very low temperatures needed in chemical modelling of the interstellar medium. We also computed these rate coefficients.

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Figure 1: Effective potentials illustrating shape and Feshbach resonances.
Figure 2: Temporal profiles of the CO beam in the beam crossing region.
Figure 3: Experimental and theoretical cross-sections for CO(j = 0) + He  CO(j = 1) + He inelastic collisions.
Figure 4: Wavefunctions squared, at the resonance energy, as a function of radial distance.

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This work extends the objectives of the ANR-12-BS05-0011-02 contract with the Agence Nationale de la Recherche and contract no. 2007.1221 with the Conseil Régional d'Aquitaine, for which financial support is acknowledged. The authors acknowledge support from Partenariat Hubert Curien van Gogh (contract 2013-28484TH). The authors thank L. Song for help with scattering calculations on the full three-dimensional SAPT potential and N. Balakrishnan for checking the results of ref. 3.

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A.B., C.N. and M.C. carried out the experimental measurements and data analysis. J.O. and A.v.d.A. performed the theoretical calculations. All authors discussed the results and contributed to the manuscript.

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Correspondence to Ad van der Avoird or Michel Costes.

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The authors declare no competing financial interests.

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Bergeat, A., Onvlee, J., Naulin, C. et al. Quantum dynamical resonances in low-energy CO(j = 0) + He inelastic collisions. Nature Chem 7, 349–353 (2015).

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