Patrick Rousseau

We investigate two nitrogen-containing isomers of polycyclic aromatic hydrocarbons, quinoline and isoquinoline, of composition C9H7N in collisions with 7 keV O+ and 48 keV O6+ projectile ions. By employing ion–ion coincidence mass spectrometry, we determine branching ratios for H-loss, C2H2-loss, and HCN-loss dissociation channels of Q2+ and IQ2+. The overall contribution of HCN loss is found to be the dominant decay channel. A comparison with the results of a parallel experiment on naphthalene, the simplest PAH, reveals that HCN loss in both isomers has a higher propensity than the analogous C2H2 loss of naphthalene. The positional identity of the nitrogen atom in the two isomers mainly manifests in many-body fragmentation of their dications. Potential energy surfaces of Q2+ and IQ2+ are further computed to explore complete fragmentation mechanisms. Parent dications (Q2+ and IQ2+) are identified to isomerize via seven-membered ring structures before elimination of C2H2 and HCN. While prompt dissociation is the primary pathway, the dominant channel of each neutral-loss class also exhibits delayed fragmentation.

We investigate two nitrogen-containing isomers of polycyclic aromatic hydrocarbons (PAHs), quinoline (Q) and isoquinoline (IQ), of composition C$_9$H$_7$N in collisions with 7~keV O$^+$ and 48~keV O$^{6+}$ projectile ions. Employing ion-ion coincidence mass spectrometry, we determine branching ratios for H-loss, C$_2$H$_2$-loss, and HCN-loss dissociation channels of Q$^{2+}$ and IQ$^{2+}$. The overall contribution of HCN-loss is found to be the dominant decay channel. A comparison with the results of a parallel experiment on naphthalene, the simplest PAH, reveals that HCN-loss in both isomers has a higher propensity than the analogous C$_2$H$_2$-loss of naphthalene. The positional identity of the nitrogen atom in the two isomers mainly manifests in many-body fragmentation of their dications. Potential energy surfaces of Q$^{2+}$ and IQ$^{2+}$ are further computed to explore complete fragmentation mechanisms. Parent dications (Q$^{2+}$ and IQ$^{2+}$) are identified to isomerize via seven-membered ring structures prior to elimination of C$_2$H$_2$ and HCN. While prompt dissociation is the primary pathway, the dominant channel of each neutral-loss class also exhibits delayed fragmentation.

The present work is a continuation of our studies with iron pentacarbonyl, a model organometallic precursor for Focused Ion Beam-Induced Deposition (FIBID). Interactions of He²⁺(16 keV), Ne⁺(6 keV), Ne⁴⁺(40 keV), Ar²⁺(12 keV) and Ar⁸⁺(64 keV) projectile ions with [Fe(CO)₅]n clusters are studied using TOF mass spectrometry. The clusters represent an intermediate between the gas phase and the bulk environment and can be used as a proxy for the processes in complex environments such as e.g. the nanostructure deposition. The addition of environment in the present study results in the observation of fragments with high kinetic energies ejected from clusters, an overall reduction of the fragmentation, and observation of a range of fragments associated with C-O bond dissociation, not observed for isolated molecules. On the other hand, the high efficiency of the Ne⁺ projectile in fragmenting the Fe(CO)₅ isolated molecule is also observed in clusters.

Bond-forming reactions induced in mixed clusters of coronene and C₆₀ by energetic impact of argon ions are modeled using molecular dynamics simulations. A wide range of reaction products and growth mechanisms are identified.

Combined experiment/theory study on ionized ferrocene molecules. We found that, due to the population of a specific long-lived excited state, charge screening effects from the iron atom and delayed fragmentations occur leading to unexpected dynamics.

We present a joint theoretical-experimental study on the inner-shell photoionization of hypoxanthine clusters in the gas phase. Simulations were performed using a computational strategy that combines molecular dynamics to explore the conformers of the clusters, density functional theory for geometry optimization and inner shell photoionization calculations. Two main intermolecular interactions are observed: hydrogen-bonds (HB) and π − π stacking. When increasing the cluster size, a combination of both kinds of interaction occurs. We show that such intermolecular interactions play a role in the chemical shift observed in X-ray photoemission spectroscopy experiments. In particular, we highlight the interplay between charge depletion and charge accumulation in regions where HBs stabilize the clusters.

In a recent work, we have shown that photon absorption can cause a chemical bond to be created between the two monomers within a protonated serine dimer, a process known as intra-cluster bond formation, despite this process not occurring following thermal excitation via low energy collision-induced dissociation (LE-CID). Here we show further evidence for non-statistical photon-induced dissociation (PID) of the protonated serine dimer. In addition we discuss LE-CID and PID studies of the protonated serine octamer, showing that in this case as well, PID leads to non-statistical fragmentation and to the formation of two bonds between three neighboring monomers.