A path that depends on the channel
When light removes an electron from NO, the ion left behind can occupy different electronic states. Electrons leaving the same molecule therefore encounter different scattering paths. What matters to me in the new experiment is that this distinction can be expressed in time: the phase difference between electronic channels changes with energy. The molecular potential can temporarily trap particular components of the electron wave. This behavior, called a shape resonance, exposes detail missing from a picture that describes release through binding energy alone.[1]
The b channel’s delay relative to the ground X channel changes from roughly 60 attoseconds at lower energy to roughly minus 50 attoseconds at higher energy. That sign change describes a changing phase relative to the selected reference. We are not directly reading an absolute residence time inside the molecule. The experiment uses interference between two-photon pathways created by extreme-ultraviolet light together with a weak infrared probing field. After accounting for the probe’s contribution, scattering calculations reproduce the energy-dependent trend, supporting the resonance interpretation.[1]
The model test lies in the difference between electronic channels. One shared emission delay cannot account for the measured energy dependence; a model needs the channel-dependent effect of the molecular potential. Agreement with calculations still leaves interactions unresolved. The theory uses independent channels and a fixed-nuclei approximation. Interchannel coupling or orientation differences unresolved by the experiment could also matter in a more detailed description. The resonance explanation gains its strength from matching a concrete phase curve within this bounded measurement.[1]
The unresolved vibrational difference
Molecular vibration supplies a second clock. When the researchers compare vibrational levels within the ground electronic state, delay differences in the non-resonant range cannot be separated from uncertainty. A distinction resolved between electronic channels remains unresolved here: different motion need not be equally visible. I do not read this as motionless nuclei. The comparison depends on particular vibrational levels, the selected energy range and lines that can be separated in the spectrum; weak overlapping lines were excluded from quantitative analysis.[1]
My inference is that a model of electron scattering needs to accommodate both observations: a delay sensitive to electronic state and an unresolved difference between vibrational levels in this experiment. Matching the striking sign change does not automatically explain the second observation. Conversely, a vibrational difference within uncertainty cannot remove vibrational effects at every energy. A smaller effect could remain below experimental resolution. Together these constraints describe more precisely which part of molecular motion is measurable at the electron’s exit.[1]