Control and imaging of O(1D2) precession

Photodissociation of S2 (X3Σg-, a1Δg, and b1Σg+) in the 320-205 nm Region

Photodissociation of vibrationally and electronically excited sulfur dimer molecules (S₂) has been studied in a combined experimental and computational quantum chemistry study in order to characterize bound-continuum transitions. Ab initio quantum chemistry calculations are carried out to predict the potential energy curves, spin–orbit coupling, transition moments, and bound-continuum spectra of S₂ for comparison with the experimental data. The experiment uses velocity map imaging to measure S-atom production following S₂ photoexcitation in the ultraviolet region (320–205 nm). A pulsed electric discharge in H₂S produces ground-state S₂ X³Σ_g^–(v = 0–15) as well as electronically excited singlet sulfur and b¹Σ_g⁺(v = 0, 1), and evidence is presented for the production and photodissociation of S₂ a¹Δ_g. In a previous paper, we reported threshold photodissociation of S₂X³Σ_g^–(v = 0) in the 282–266 nm region. In the present study, S(³P_J) fine structure branching and angular distributions for photodissociation of S₂ (X³Σ_g^–(v = 0), a¹Δ_g and b¹Σ_g⁺) via the B″³Π_u, B³Σ_u^– and 1¹Π_u excited states are reported. In addition, photodissociation of the X³Σ_g^–(v = 0) state of S₂ to the second dissociation limit producing S(³P₂) + S(¹D) is characterized. The present results on S₂ photodynamics are compared to those of the well-studied electronically isovalent O₂ molecule.

Multi-mass velocity-map imaging studies of photoinduced and electron-induced chemistry

Multi-mass velocity-map imaging (VMI) is becoming established as a promising method for probing the dynamics of a variety of gas-phase chemical processes. We provide an overview of velocity-map imaging and multi-mass velocity-map imaging techniques, highlighting examples in which these approaches have been used to provide mechanistic insights into a range of photoinduced and electron-induced chemical processes. Multi-mass detection capabilities have also led to the development of two new tools for the chemical dynamics toolbox, in the form of Coulomb-explosion imaging and covariance-map imaging. These allow details of molecular structure to be followed in real time over the course of a chemical reaction, offering the tantalising prospect of recording real-time 'molecular movies' of chemical dynamics. As these new methods become established within the reaction dynamics community, they promise new mechanistic insights into chemistry relevant to fields ranging from atmospheric chemistry and astrochemistry through to synthetic organic photochemistry and biology.

Taming molecular collisions using electric and magnetic fields

In molecular collision experiments, studying the collision process in high detail requires controlling molecular degrees of freedom before the collision.