Photoinduced water splitting in pyridine water clusters.

Ab initio calculations predict that pyridine (Py) can act as a photo-catalyst to split water by the absorption of a UV photon following the reaction Py-HO + hν → PyH˙ + OH˙. To test this prediction, we performed two types of experiments: in the first, we characterize the electronic spectroscopy of the PyH˙ radical in the gas phase. In the second, we evidence the reaction through the UV excitation of molecular Py-(HO) clusters obtained in a supersonic expansion and monitoring the PyH˙ reaction product.

Excited state of protonated benzene and toluene.

We present photo-fragmentation electronic spectra of the simplest protonated aromatic molecules, protonated benzene and toluene, recorded under medium resolution conditions and compared with the photo-fragmentation spectrum of protonated pyridine. Despite the resolution and cold temperature achieved in the experiment, the electronic spectra of protonated benzene and toluene are structure-less, thus intrinsically broadened. This is in agreement with the large geometrical changes and the fast dynamic toward internal conversion predicted by ab initio calculations for protonated benzene [Rode et al.

UV spectroscopy of cold ions as a probe of the protonation site.

The best determination of the most stable protonation site in aromatic molecules relies nowadays on the IR spectroscopy and ab initio calculations. It appears that these methods are not necessarily unambiguous and cannot always be safely employed. We present in this paper an example showing that electronic spectroscopy of cold ions complemented with ab initio calculations gives clear results on the protonation site.

Plasmonic graded-chains as deep-subwavelength light concentrators.

We have studied the plasmonic properties of aperiodic arrays of identical nanoparticles (NPs) formed by two opposite and equal graded-chains (a chain where interactions change gradually). We found that these arrays concentrate the external electromagnetic fields even in the long wavelength limit. The phenomenon was understood by identifying the system with an effective cavity where plasmonics excitations are trapped between effective band edges, resulting from the change of passband with the NP's position.