Ionic dynamics underlying strong-field dissociative molecular ionization

Abstract

We study strong field molecular ionization, with a focus on indirect ionization to dissociative excited ionic states. Indirect ionization, also known as post-ionization excitation, refers to the excitation of the molecular cation following ionization to a lower lying state. We propose two possible mechanisms underlying indirect ionization -resonant transitions facilitated by nuclear dynamics and non-adiabatic transitions driven by the laser field off resonance. We compare them by measuring the dependence of the indirect ionization yield on pulse duration for cations with different electronic structures. Both experiments and simulations confirm the importance of nuclear dynamics in indirect ionization and indicate the presence of off-resonant non-adiabatic transitions.

Sequential and direct ionic excitation in the strong-field ionization of 1-butene molecules

“…We remark that nuclear dynamics was very recently confirmed to play a role in post-ionization excitation. 50,51 Future studies of the correlated photoelectron spectra as a function of intensity, pulse duration, and wavelength within a pump-probe scheme would be very helpful for developing a deeper understanding, in particular for photon energies above the gap energy. Finally, it would be interesting to explore how general our conclusions are by performing similar studies in other molecular systems.…”

Gaining Mechanistic Insight with Control Pulse Slicing: Application to the Dissociative Ionization of CH2BrI

“…The collective observations in CPS(+) and CPS(−) suggest that, while the early portion of the pulse plays a role in the ultimate yield enhancement of Br + and I + involving intermediate neutral dynamics, the late portion of the pulse is responsible for the reduced yields in CH 2 Br + and CH 2 I + involving dynamics on the ionic surface. 42 Further examining the temporal structure of the full control pulses B and C shown in the background of Figure 5, it is evident that pulse B, which maximizes the objective ratio of Br + /CH 2 Br + , contains complex pulse structure over its entire temporal range; in contrast, pulse C, which produces a lower product ratio, is almost free of late-pulse features beyond ∼500 fs. Examination of these pulses further supports the CPS interpretation that, the late-pulse structure plays a central role in controlling the objective yield of Br + /CH 2 Br + .…”

“…The collective observations in CPS­(+) and CPS(−) suggest that, while the early portion of the pulse plays a role in the ultimate yield enhancement of Br + and I + involving intermediate neutral dynamics, the late portion of the pulse is responsible for the reduced yields in CH 2 Br + and CH 2 I + involving dynamics on the ionic surface …”

On the preservation of coherence in the electronic wavepacket of a neutral and rigid polyatomic molecule

“…Experimental and theoretical works [22][23][24][25][26][27] on molecular fragmentation triggered by ionization suggest a positive answer to this question. Sudden ionization of a molecule creates a coherent superposition of electronic states, leading to ultrafast charge migration [28][29][30][31][32][33].…”