Simultaneous imaging of vibrational, rotational, and electronic wave packet dynamics in a triatomic molecule (2408.07958v3)

Abstract: Light-induced molecular dynamics often involve the excitation of several electronic, vibrational, and rotational states. Since the ensuing electronic and nuclear motion determines the pathways and outcomes of photoinduced reactions, our ability to monitor and understand these dynamics is crucial for molecular physics, physical chemistry, and photobiology. However, characterizing this complex motion represents a significant challenge when different degrees of freedom are strongly coupled. In this Letter, we demonstrate how the interplay between vibrational, rotational, and electronic degrees of freedom governs the evolution of molecular wave packets in the low-lying states of strong-field-ionized sulfur dioxide. Using time-resolved Coulomb explosion imaging (CEI) and quantum mechanical wave packet simulations, we directly map the bending vibrations of the molecule, show how the vibrational wave packet is influenced by molecular alignment, and elucidate the consequences of nuclear motion for the coupling between the two lowest electronic states of the cation. Our results demonstrate that multi-coincident CEI can be an efficient experimental tool for characterizing coupled electronic and nuclear motion in polyatomic molecules.

• The paper employs time-resolved Coulomb explosion imaging combined with simulations to directly visualize coupled vibrational, rotational, and electronic wave packet dynamics in SO2, specifically imaging bending vibrations.
• The study quantifies how aligning the molecular axis with the laser field significantly impacts both ionization and dissociation pathways.
• The research highlights the crucial role of passing through a conical intersection in coupling different vibrational modes and influencing fragment ion energy distributions.

Imaging Coupled Wave Packet Dynamics in Triatomic Molecules

The paper entitled "Imaging coupled vibrational, rotational, and electronic wave packet dynamics in a triatomic molecule" presents a detailed paper of the intricate dynamics of wave packets in sulfur dioxide (SO$_2$), a triatomic molecule known for its atmospheric significance and complex photochemistry. This research focuses on the interplay between vibrational, rotational, and electronic motions that govern the molecular wave packet evolution in the context of strong-field ionization.

The authors have employed time-resolved Coulomb explosion imaging (CEI) in conjunction with quantum mechanical wave packet simulations to directly visualize bending vibrations and the influence of molecular alignment in ionized SO$_2$. CEI offers high temporal resolution and sensitivity to light atoms, which is beneficial for capturing the swift and complex dynamics potentially overlooked by other imaging techniques such as ultrafast electron diffraction or X-ray scattering. The use of coincidence imaging for obtaining multi-dimensional data is a formidable approach that allows researchers to separate various reaction pathways efficiently.

A primary focus of the paper is dissecting the vibrational dynamics induced by strong-field ionization leading to the formation of a coherent vibrational wave packet in SO$_2^+$ showcasing dominant bending mode oscillations at approximately 400 cm$^{-1}$. The research shows that these atomic-scale movements can be effectively visualized in the laboratory frame, emphasizing CEI's potential to capture dynamic structural information at atomic resolutions traditionally challenging to achieve.

Further, the alignment of the molecular axis with respect to the laser polarization plays a crucial role in the dynamics observed. As the rotational wave packet aligns with the laser field, the molecular geometry significantly affects both the ionization and dissociation pathways. The paper quantifies these effects, illustrating how initial molecular alignments influence the fragmentation processes and correlate with the yields of various ion channels.

A notable aspect covered in the paper is the excitation to the first excited state of the cation and the subsequent traversal of a conical intersection (CI). The paper reveals the transformative role this CI plays in coupling different vibrational modes, notably the asymmetric stretch, causing distinct kinetic energy signatures in fragment ion distributions. Such insights present a nuanced understanding of nonadiabatic transitions relevant for chemically relevant systems.

The implications of this research are manifold. From a theoretical perspective, the findings contribute to the broader understanding of coupled nuclear and electronic degrees of freedom and their interplay via nonadiabatic interactions. Practically, the results endorse CEI as a robust tool for visualizing molecular dynamics, extending its applicability to more complex polyatomic molecules. Future explorations may benefit from the methodologies and conclusions drawn here, particularly in refining time-resolved imaging techniques and simulations of molecular wave packets.

Overall, this paper advances the knowledge frontier in molecular dynamics by intricately mapping and interpreting the influence of various motions on wave packet evolution. Future studies could explore a wider array of triatomic and more complex polyatomic molecules, shedding light on how CEI can unravel the sophisticated choreography of molecular dynamics relevant in fields such as reaction chemistry and atmospheric sciences.