J.-P. Visticot

Two-electron pseudopotential investigation of the electronic structure of the CaAr molecule

The electronic structure of the Ca-Ar molecule is investigated using [Ca2+] and [Ar] core pseudopotentials complemented by core polarization operators on both atoms, considering the molecule to be a two-electron system. The electronic two-body problem is solved by achieving a full configuration interaction with extensive Gaussian basis sets. The potential energy curves and the molecular constants of all CaAr states dissociating into atomic configurations ranging between the ground state 4s2u200a1S and the doubly excited state 4p2u200a3P are determined. Spin–orbit coupling is also included in an atom-in-molecule scheme for states dissociating into the 4s4p and 4s3d configurations. The present theoretical results show good overall agreement with experimental data. They also help to clarify the very complicated spectroscopy of the CaAr system in the 38u200a000u2009cm−1 energy range where many states correlated with the 4s4d, 3d4p, and 4p2 atomic configurations interact with or cross one another. As a by-product of the prese...

Transition state in metal atom reactions

The observation of the transition state in metal molecule reactions has been approached by several experimental methods, crossed beams, transition state spectroscopy and more briefly via time dependent femtosecond localization. The chemistry is far richer than the one-dimensional harpoon model involving an instant single electron jump imagined at the origin.

Probing several structures of Fe(H2O)n+ and Co(H2O)n+ (n=1,...,10) cluster ions

Co(H2O)n≤10+ and Fe(H2O)n≤10+ cluster ions were generated in a source combining laser ablation and a supersonic expansion. The clusters were fragmented to get insight into their structure. Two questions were addressed: first, the arrangement of the water molecules about the metal ion, and second, the electronic properties of the solvated metal ion. Collision induced dissociation by helium was used to answer the first question, especially for the smallest clusters with n=2 and 3. This revealed the existence of filament structures where one water molecule lies in the second solvation shell about the metal ion although the first shell is not filled. The binding energies of second shell water in Co(H2O)2+ and Fe(H2O)2+ are 0.45±0.1 and 0.5±0.1 eV, respectively. The answer to the second question was provided by photofragmentation experiments where the cluster ions are illuminated at 532, 355 and 266 nm. The most striking effect is seen with cobalt ions where increasing the number n of water molecules above n=7 allows one to built up an absorption band that is known when Co+ is solvated in liquid water. The two fragmentation techniques appear as complementary.

Dynamics of the barium-molecule system within large argon clusters

The effects of adding molecules on the LIF at 540 nm of a barium atom at the surface of an argon cluster (average size 420) has been investigated. We showed that molecules like ethanol,n-hexane and O2 from stable complexes with ground state barium. In the case of molecules like N2, CH4 and SF6, the collisional quenching of solvated Ba(1P) is observed. The large quenching rates obtained are interpreted by a surface mobility of the collisional partners. Moreover, we showed that this collisional quenching leads to the ejection of free Ba(3P1).

Spectroscopy and dynamics of calcium dimers deposited on large argon and neon van der Waals clusters

Laser-induced-fluorescence studies of calcium dimer deposited on large argon and neon clusters have been performed. The spectroscopy of the Ca2u200aA state is slightly perturbed by the cluster surface leading to shifts and broadenings of the order or less than 100 cm−1. An absorption has been evidenced in the 530–550 nm wavelength range that is tentatively assigned to the yet undocumented Au200a′1Πu state of Ca2 correlating to the Ca(1D)+Ca(1S) asymptotic limit. The excited calcium dimer dynamics are very different in neon and argon clusters. The argon cluster is much more efficient for electronic and vibrational relaxation of the excited dimer. Finally, excitation in the blue of the calcium atomic resonance line leads to a competition between dissociation of the dimer with ejection of an excited calcium atom out of the cluster and the relaxation of the dimer to lower excited levels.

Excited state reactions of metals on clusters: Full dynamics of the Ca*+HBr reaction on Ar2000

We report on the Ca*+HBr→CaBr*+H reaction when photoinduced within a Ca⋯HBr complex that is deposited at the surface of a large argon cluster (surface complex). The excitation that turns on the reaction is localized on the calcium atom. Information on the dynamics of the reaction is provided by observing the CaBr fluorescence while scanning the excitation laser across the calcium resonance line. This provides information on the access to the transition region of the reaction and helps to clarify how the argon cluster influences this access as compared to the gas phase experiment where the Ca⋯HBr complex is free (free complex). Chemiluminescence spectra were also recorded to characterize the output channel of the reaction. Not surprisingly, the presence of the cluster affects the dynamics of the reaction that proceeds at its surface. Several effects have been identified. Depending on which potential energy surface of the Ca⋯HBr complex is excited by the laser, the cluster acts passively or actively. When t...

Reactions of N2O with Lin in the gas-phase and on the surfaces of large Arn clusters

Abstract N 2 O was reacted with Li n species both in the gas-phase under single-collision conditions and on the surface of large Ar n ( n ≈4000) clusters. In the gas-phase, a broad emission (410–730 nm) was attributed to LiOLi ( A 1 B 1 ) product from the reaction of Li 2 . The same reaction on clusters leads a similar emission, but weaker to the blue. It is due to LiOLi ( A 1 B 1 ) also, but cooled before ejection off the cluster. Strong Li (2 p 2 P ) emission is also observed in the cluster experiment presumably due to the reaction Li 3 + N 2 O → LiOLi ( X 1 Σ g + )+ Li (2 p 2 P )+ N 2 where Li (2 p 2 P ) is ejected into the gas-phase.