Dissociative Dynamics in Molecular Ion Collisions

Dissociative dynamics in molecular ion collisions encompasses the processes by which a molecular ion and an electron or neutral partner interact, leading to fragmentation into neutral and charged atomic or molecular fragments. These collisions proceed via direct pathways, in which the incident particle transiently populates a dissociative state of the neutral complex, and indirect pathways, which involve capture into Rydberg states followed by non-adiabatic transitions and subsequent dissociation. Theoretical treatments typically employ multichannel quantum defect theory (MQDT), R-matrix methods and close-coupling approaches to account for resonant structures, non-local autoionisation and rovibrational couplings. Experimentally, merged-beam and storage-ring techniques provide state-resolved cross sections and rate coefficients over a wide energy range. Understanding these processes is critical for modelling the chemistry of cold interstellar clouds, controlling edge plasma behaviour in fusion reactors and interpreting planetary ionospheres. Interdisciplinary collaboration between theory and experiment has led to refined potential energy surfaces and coupling matrices, enabling predictive models of reaction outcomes under varied temperature and density regimes.

Research from Nature Portfolio

No recent Nature Portfolio content available.

Research from all publishers

Recent studies of dissociative recombination of NS+ with slow electrons have provided detailed cross sections and temperature-dependent rate coefficients relevant to interstellar cloud conditions between 10 K and 1000 K. The results reveal moderate recombination rates, about half those previously assumed, and underline the importance of accurate data for astrochemical models. Advanced MQDT calculations have been used to quantify uncertainties and compare isovalent species, highlighting subtle electronic effects on fragmentation pathways. Investigations into electron collisions with HD+ have introduced a comprehensive close-coupling methodology in a strict diabatic representation, rigorously including non-adiabatic couplings among bound states and a non-local complex potential to describe autoionisation. This approach yields state-resolved final-state distributions for dissociative recombination and ion-pair formation, showing excellent agreement with experimental measurements and offering a unified framework for reactive scattering in simple diatomics. A revisited theoretical study of N2H+ dissociative recombination has employed a two-step MQDT and R-matrix approach, first using a one-dimensional frozen-bond model to assess indirect mechanisms and then a three-dimensional normal-mode treatment. The latter reproduces storage-ring cross sections with high fidelity at very low energies, emphasising the role of bending modes and multiple dissociative routes in achieving quantitative agreement with experiment.

Dissociative Dynamics in Molecular Ion Collisions publication trend

The graph below shows the total number of articles in dissociative dynamics in molecular ion collisions across all publications each year (not limited to Nature Index journals).

Technical terms

Multichannel Quantum Defect Theory (MQDT): A quantum-mechanical framework for calculating resonant and non-resonant collision cross sections by partitioning short-range interactions and long-range Coulombic behaviour.

R-matrix method: A computational approach dividing configuration space into an inner region, where complex electron-molecule interactions occur, and an outer region, where scattering is simpler.

Non-adiabatic coupling: Interactions that allow transitions between electronic states when nuclear motion mixes these states, enabling indirect dissociation pathways.

Rate coefficient: A temperature-dependent parameter that quantifies the probability per unit time of a given collision-induced process in a plasma or gas.

Potential energy surface (PES): A multidimensional surface representing the electronic energy of a molecular system as a function of nuclear coordinates, governing reaction dynamics.

Autoionisation: A process in which a transiently formed neutral molecule in a high-lying electronic state spontaneously ejects an electron, competing with dissociation.

References

1. Dissociative recombination and resonant ion-pair formation in electron collisions with HD+. Physical Review A (2024).
2. Dissociative recombination of NS+ in collision with slow electrons. Journal of Physics B Atomic Molecular and Optical Physics (2024).
3. Dissociative recombination of N2H+: a revisited study. The European Physical Journal Special Topics (2023).