1.5-Femtosecond Delay in Charge Transfer

TL;DR

This study demonstrates a measurable 1.46 femtosecond delay in charge transfer between quantum states caused by coupling to additional states, challenging the assumption of instantaneous population transfer in real systems.

Contribution

The paper provides the first direct measurement of a femtosecond-scale delay in charge transfer due to multi-state coupling, supported by advanced spectroscopy and quantum calculations.

Findings

Measured a 1.46 fs delay in charge transfer in CF3I+

Resolved vibrational rearrangement time of 9.38 fs

Determined population transfer time of 2.3-2.4 fs

Abstract

The transfer of population between two intersecting quantum states is the most fundamental dynamical event that governs a broad variety of processes in physics, chemistry, biology and material science. Whereas any two-state description implies that population leaving one state instantaneously appears in the other state, we show that coupling to additional states, present in all real-world systems, can cause a measurable delay in population transfer. Using attosecond spectroscopy supported by advanced quantum-chemical calculations, we measure a delay of 1.46$\pm$0.41 fs at a charge-transfer state crossing in CF$_3$I$^+$, where an electron hole moves from the fluorine atoms to iodine. Our measurements also fully resolve the other fundamental quantum-dynamical processes involved in the charge-transfer reaction: a vibrational rearrangement time of 9.38$\pm$0.21 fs (during which the vibrational wave packet travels to the state crossing) and a population-transfer time of 2.3-2.4 fs. Our experimental results and theoretical simulations show that delays in population transfer readily appear in otherwise-adiabatic reactions and are typically on the order of 1 fs for intersecting molecular valence states. These results have implications for many research areas, such as atomic and molecular physics, charge transfer or light harvesting.