1. Could you explain the significance of your article to the non-specialist? 

Photodissociation provides a sensitive, and selective, way to study the potentials that control the forces within molecules and the interactions between potentials. Of particular interest are multiple surface dissociations, with the possibility of forming photodissociation products via different paths, with resulting quantum mechanical coherences. We have used a high-resolution laser technique to measure the orientation of rotating diatomic photofragments (i.e. the clockwise or anti-clockwise sense of rotation) created by circularly polarized light, and how this orientation changes with the recoil direction. This effect provides a distinctive signature of the sources of rotational excitation, including the processes which may lead to coherence. 

2. What has motivated you to conduct this work? 

We had earlier developed a very low-noise method of measuring Doppler-resolved absorption spectra of photofragments and applied it to observing the CN product from the photodissociation of ICN, a classic and deeply studied case of photodissociation involving multiple excited states. Using only linearly polarized light, we found it possible to explain all of the observations without interference effects, despite superimposed paths. There has been much interest in the last few years in the photodissociation of diatomic molecules, and the orientation arising in the product atoms from coherence. The theory of these effects is challenging, but it is clear that circularly polarized probe techniques are the essential tools to interrogate the interferences between parallel and perpendicular excitation paths to the same products. This motivated us to extend our previous work to study the orientation. 

3. Where do you see this work developing in the future? 

It seems clear that that we have not yet seen examples of all the effects that can be anticipated from circularly polarized photodissociation of small molecules. We expect future experiments to produce new surprises, and to stimulate further theoretical descriptions of the coherent processes in molecular photodissociation. The ideas and methods developed in this area also bear directly on issues involved in phase control of branching ratios. 

4. Are there any particular challenges facing future research in this area? 

This is very much a field where careful experiments and extension of theory go hand-in-hand, and we hope that these experimental observations will stimulate our theoretical colleagues.