Steven Cavanagh

High-resolution photoelectron spectroscopy of linear ← bent polyatomic photodetachment transitions: The electron affinity of CS2

A combination of high-resolution velocity-map-imaging photoelectron spectroscopy and isotopic substitution is used to show that precise electron affinities can be obtained from polyatomic photodetachment spectra, even for cases involving significant changes in equilibrium geometry between the molecular neutral and anion. The chosen example CS(2) (X (1)Σ(g)(+)) (linear) ← CS(2)(-) (X (2)A(1)) (bent) photodetachment transition is found to preferentially access highly-excited v(2) (bending) levels of the neutral, with no observation possible of the lowest-v(2) bands. Nevertheless, through (13)C isotopic substitution, the v(2) numbering is established unambiguously and the adiabatic electron affinity of CS(2) is found to be 4456(10) cm(-1) [0.5525(13) eV], by far the most precise value reported to date.

Photodetachment of O− from threshold to 1.2 eV electron kinetic energy using velocity-map imaging

High-resolution photoelectron imaging from O− with excess energies between 0.5 meV and 1.2 eV is reported. With electron energy resolutions ranging from 266 μeV to 3 meV, branching ratios and angular-distribution asymmetry parameters for each of the fine-structure transitions were measured. Preliminary data for a subset of these measurements showing possible effects due to electron correlation at low excess energy are presented, in the hope of stimulating further theoretical calculations for this species.

Approaching the O− photodetachment threshold with velocity-map imaging

A series of photodetachment spectra from O− has been measured from near threshold to several eV using the technique of velocity-map imaging. With a resolving power of ΔE/E ≤ 0.38%, the energy and angular dependences for the six fine-structure transitions have been determined. For the first time, the energy and angular dependences of the cross section within a few meV of threshold have been determined.

Back to basics, the chemistry of aerosol formation, viewed with velocity-map imaging of photoelectrons

Advances in charged particle imaging techniques provide new avenues to examine chemical mechanisms that may be responsible for the formation of sulfuric acid aerosols, known to have a role in moderating the effects of global warming.

Rotationally resolved photodetachment spectrum of OH−, exposed with velocity-map imaging

The photodetachment spectrum of OH− has been measured using velocity-map imaging for the detection of photoelectrons. The relative electron kinetic-energy resolution, determined to be (ΔE/E) = 0.5%, resolves individual rotational transitions, including R3(0) that defines the electron affinity. Previously unobserved, N-, O-, S-, T-branch transitions are also revealed. The angular anisotropy parameters in general exhibit values consistent with electron detachment from O−, β ≈ −0.8, except for the S, T branches which are significantly more isotropic, with β ≈ −0.4.

Vibration-dependent angular anisotropy in the photodetachment of O2−, viewed with velocity-map imaging

The photodetachment spectrum of O2− has been measured at a number of wavelengths using velocity-map imaging. The electron kinetic-energy resolution (< 5 meV) is sufficient to resolve the anion fine-structure splitting, vibrational and electronic structure. The electron angular distribution varies with the electron kinetic-energy, with a different behaviour for each vibronic band.