E. Jacquet

Spectroscopic properties of alkali atoms embedded in Ar matrix.

We present a theoretical investigation of visible absorption and related luminescence of alkali atoms (Li, Na, and K) embedded in Ar matrix. We used a model based on core polarization pseudopotentials, which allows us to determine accurately the gas-to-matrix shifts of various trapping sites. The remarkable agreement between our calculated results and the experimental spectra recorded by several authors allows us to establish a clear assignment of the observed spectra, which are made of contributions from crystalline sites on the one hand, and of grain boundary sites on the other hand. Our study reveals remarkably large Stokes shifts, up to 9000 cm(-1), which could be observed experimentally to identify definitely the trapping sites.

An accurate model potential for alkali neon systems

We present a detailed investigation of the ground and lowest excited states of M-Ne dimers, for M=Li, Na, and K. We show that the potential energy curves of these Van der Waals dimers can be obtained accurately by considering the alkali neon systems as one-electron systems. Following previous authors, the model describes the evolution of the alkali valence electron in the combined potentials of the alkali and neon cores by means of core polarization pseudopotentials. The key parameter for an accurate model is the M(+)-Ne potential energy curve, which was obtained by means of ab initio CCSD(T) calculation using a large basis set. For each MNe dimer, a systematic comparison with ab initio computation of the potential energy curve for the X, A, and B states shows the remarkable accuracy of the model. The vibrational analysis and the comparison with existing experimental data strengthens this conclusion and allows for a precise assignment of the vibrational levels.

Solvation of Na2+ in Arn clusters. I. Structures and spectroscopic properties

We present a theoretical study of Na(2) (+) solvation in an argon matrix Ar(n) for n=1 to a few tens. We use a model based on an explicit description of valence electron interaction with Na(+) and Ar cores by means of core polarization pseudopotential. The electronic structure determination is thus reduced to a one-electron problem, which can be handled efficiently. We investigate the ground state geometry and related optical absorption of Na(2) (+)Ar(n) clusters. For n<or=5, the lowest energy isomers are obtained by aggregation of Ar atoms at one single extremity of Na(2) (+), leading to moderate perturbation of the optical transition. For 6<or=n<or=15, the Ar atoms aggregate at both extremities. This structural change is associated with a strong blueshift of the first optical transition (X (2)Sigma(g) (+)-->A (2)Sigma(u) (+)), which reveals the confinement of the excited A (2)Sigma(u) (+) state. The Na(2) (+) energy spectrum is so strongly perturbed that the A (2)Sigma(u) (+) state becomes higher than the B (2)Pi(u) (+) states. The closure of the first solvation shell is observed at n=17. Above this size, the second solvation shell develops. Its structure is dominated by a pentagonal organization around the Na(2) (+) molecular axis. The optical transitions vary smoothly with n and the A (2)Sigma(u) (+) and B (2)Pi(u) states are no longer inverted, though the first optical transition remains strongly blueshifted.

Structure and photoabsorption properties of cationic alkali dimers solvated in neon clusters

We present a theoretical investigation of the structure and optical absorption of M(2)(+) alkali dimers (M=Li,Na,K) solvated in Ne(n) clusters for n=1 to a few tens Ne atoms. For all these alkali, the lowest-energy isomers are obtained by aggregation of the first Ne atoms at the extremity of the alkali molecule. This particular geometry, common to other M(2)(+)-rare gas clusters, is intimately related to the shape of the electronic density of the X  (2)Σ(g)(+) ground state of the bare M(2)(+) molecules. The structure of the first solvation shell presents equilateral Ne(3) and capped pentagonal Ne(6) motifs, which are characteristic of pure rare gas clusters. The size and geometry of the complete solvation shell depend on the alkali and were obtained at n=22 with a D(4h) symmetry for Li and at n=27 with a D(5h) symmetry for Na. For K, our study suggests that the closure of the first solvation shell occurs well beyond n=36. We show that the atomic arrangement of these clusters has a profound influence on their optical absorption spectrum. In particular, the XΣ transition from the X  (2)Σ(g)(+) ground state to the first excited (2)Σ(u)(+) state is strongly blueshifted in the Frank-Condon area.

Nonadiabatic molecular dynamics of photoexcited Li 2+ Ne n clusters

We investigate the relaxation of photoexcited Li(2)(+) chromophores solvated in Ne(n) clusters (n = 2-22) by means of molecular dynamics with surface hopping. The simplicity of the electronic structure of these ideal systems is exploited to design an accurate and computationally efficient model. These systems present two series of conical intersections between the states correlated with the Li+Li(2s) and Li+Li(2p) dissociation limits of the Li(2)(+) molecule. Frank-Condon transition from the ground state to one of the three lowest excited states, hereafter indexed by ascending energy from 1 to 3, quickly drives the system toward the first series of conical intersections, which have a tremendous influence on the issue of the dynamics. The states 1 and 2, which originate in the Frank-Condon area from the degenerated nondissociative 1(2)Π(u) states of the bare Li(2)(+) molecule, relax mainly to Li+Li(2s) with a complete atomization of the clusters in the whole range of size n investigated here. The third state, which originates in the Frank-Condon area from the dissociative 1(2)Σ(u)(+) state of the bare Li(2)(+) molecule, exhibits a richer relaxation dynamics. Contrary to intuition, excitation into state 3 leads to less molecular dissociation, though the amount of energy deposited in the cluster by the excitation process is larger than for excitation into state 1 and 2. This extra amount of energy allows the system to reach the second series of conical intersections so that approximately 20% of the clusters are stabilized in the 2(2)Σ(g)(+) state potential well for cluster sizes n larger than 6.

Electron capture into N4+(1s2nl) subshells during N5+-Li collisions at 40-120 keV

We have recorded photon spectra during collisions between N5+ ions and lithium atoms in the range 200-600 nm at different projectile energies (40-120 keV). The spectral resolution allowed the determination of capture cross sections of nl subshells with principal quantum numbers n=6, 7 and 8. The experimental results are compared to calculations using the three-body classical trajectory Monte Carlo method (CTMC). On the whole, a good agreement between experimental and CTMC calculated results is obtained. The influence of the projectile core electrons is examined comparing CTMC calculations for the B5+-Li collision system to those for N5+-Li. A small but not negligible core-electron effect is observed which manifests itself mainly in the population of the N4+(ns) subshells.

Ultra-light extensometer for the assessment of the mechanical properties of the human skin in vivo

This paper aims to present an ultra‐light extensometer device dedicated to the mechanical characterization of the human skin in vivo.

Potential energy curves and spin-orbit coupling of light alkali-heavy rare gas molecules

The potential energy curves of the X, A, and B states of alkali-rare gas diatomic molecules, MKr and MXe, are investigated for M = Li, Na, K. The molecular spin-orbit coefficients a(R)=<(2)Π(½)|Ĥ(SO)|(2)Π(½)> and b(R)=<(2)Π(-½)|Ĥ(SO)|(2)Σ(½)> are calculated as a function the interatomic distance R. We show that a(R) increases and b(R) decreases as R decreases. This effect becomes less and less important as the mass of the alkali increases. A comparison of the rovibrational properties deduced from our calculations with experimental measurements recorded for NaKr and NaXe shows the quality of the calculations.

Polarized light emission during very slow - Li(2s) collisions ()

We report on the polarization of lines emitted by excited ions produced by the single-electron capture process during collisions at very low impact energies (E = 0.1 - 1.0). The polarization degrees of lines corresponding to and transitions were measured and were compared with theoretical polarization degrees obtained from distributions calculated by using the classical trajectory Monte Carlo (CTMC) method. A remarkable energy dependence is observed in both the experimental and theoretical results at very low projectile velocity. A qualitative discussion based on the relative importance of the different dynamical couplings is proposed.

Velocity effect in the l-distribution of the electron capture in collisions of highly charged Ar8+ ions with a Li(2s) target

Abstract The effect of the velocity of the incident ions in the l-distributions of the electron capture in collisions of highly charged Ar8+ ions with a Li(2s) target is studied. These Ar8+Li collisions are experimentally studied by means of near UV and visible photon spectroscopy (200–600 nm) and theoretically analysed by means of the three-body classical trajectory Monte Carlo method. In addition to the effect of the projectile core, we show that the final nl-distributions are, for the most populated n = 8 and n = 9 states, strongly energy dependent.