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Multidimensional scrambling

Phys. Rev. Lett. 120, 103401 (2018)

2D infrared spectroscopy is an optical analogue of NMR spectroscopy, using photon echoes instead of spin echoes. The technique dispenses with the need for magnetic fields, and offers sub-picosecond resolution, but the ultrafast dynamics can give rise to complex line shapes due to environmental interactions. Such interactions are easily controlled in gases, so the approach is well suited to quasi-free molecules, for which it can resolve rotational contributions and separate intra- from intermolecular contributions. Now, Larry Ziegler and co-workers have used it to show that a rotational substructure can equilibrate in just two intermolecular collisions.

Ziegler et al. temporally resolved the two rotational sub-bands of an infrared transition in a dilute gas, showing that these contributions give rise to new spectral features and dynamics. Using rotational spectral diffusion occurring on a picosecond timescale, the authors resolved an efficient way in which the molecule redistributes energy — so-called J scrambling — that is unresolvable in condensed-matter samples.

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Correspondence to Jan Philip Kraack.

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Kraack, J.P. Multidimensional scrambling. Nature Phys 14, 328 (2018).

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