Filming non-radiative population transfer: Time-resolved x-ray scattering near an avoided crossing

TL;DR

This paper demonstrates how time-resolved x-ray scattering can reveal ultrafast nuclear dynamics and interference effects in molecules undergoing non-radiative population transfer at an avoided crossing, offering new insights into excited state transitions.

Contribution

It introduces a novel experimental approach to visualize nuclear wavepacket interference during non-adiabatic transitions in molecules.

Findings

Ultrafast changes in scattering pattern angular distribution observed.

Reconstructed a movie of nuclear probability density from interference.

Experimental evidence of non-adiabatic coupling effects in iodine.

Abstract

We show that time-resolved x-ray scattering from molecules prepared in a superposition of electronic states moving through an avoided crossing has new features not found in diffraction from the corresponding classical mixed state. Photoabsorption in molecular iodine at 520 nm produces a superposition of two dipole-allowed nearly degenerate electronic states, which interact due to non-adiabatic coupling. We show experimental evidence that the mixing of the nuclear wavepackets from the two electronic states at the avoided crossing leads to ultrafast changes in the angular composition of the scattering pattern. This provides a novel means to study transitions in excited molecular systems. We reconstruct a movie of the nuclear probability density arising from this interference.