62 research outputs found
Nucleation of a sodium droplet on C60
We investigate theoretically the progressive coating of C60 by several sodium
atoms. Density functional calculations using a nonlocal functional are
performed for NaC60 and Na2C60 in various configurations. These data are used
to construct an empirical atomistic model in order to treat larger sizes in a
statistical and dynamical context. Fluctuating charges are incorporated to
account for charge transfer between sodium and carbon atoms. By performing
systematic global optimization in the size range 1<=n<=30, we find that Na_nC60
is homogeneously coated at small sizes, and that a growing droplet is formed
above n=>8. The separate effects of single ionization and thermalization are
also considered, as well as the changes due to a strong external electric
field. The present results are discussed in the light of various experimental
data.Comment: 17 pages, 10 figure
Molecular picture of excited states and fragmentation paths of the Na
The stability against fragmentation and possible relaxation of the
lowest excited states of the Na5F4
cluster (representative of cubic non stoechiometric clusters with an
excess sodium atom, also called sodium-tail) is investigated
by means of one-electron pseudopotential calculations with particular
reference to photoabsorption processes from the ground state. Whereas
the equilibrium configuration of the ground state has C3v
symmetry, the doubly degenerate 12E excited state is affected by
a conical intersection and a Jahn-Teller effect associated with the
rotation of the sodium tail around the C3-axis. This yields
a "Mexican hat" topology for the lowest sheet with three equivalent
Cs minima. Alternatively the 22A1 state has a minimum retaining
the C3v symmetry. The dissociation paths of the cluster along the
C3-axis into respectively Na4F4 + Na and Na4F3 + NaF
are also investigated. Among the former paths, the excited
states are found adiabatically stable with respect to the products.
However in the A1 symmetry, fragmentation into NaF exhibits an
interesting avoided crossing between configurations correlated
respectively with Na4F3
+ + NaF- and Na4F3 + NaF.
Such interaction, similar to the well-known charge exchange processes
in elementary molecules might induce non adiabatic predissociation of
the 22A1 state. This mechanism is invoked to explain the
differences between R2PI and depletion spectra, correlated with the
dissociation or relaxation of the excited states
Calcul théorique en couplage Λ-Σ du spectre électronique des excimères Ar2 et Kr2 corrélé aux configurations atomiques np5(n + 1) s et np5( n + 1) p
Adiabatic potential curves for Ar (3p6 1S0) + Ar* (3p5 4s, 3p5 4p) and Kr(4p6 1 S0) + Kr* (4p5 5s, 4p5 5p) are determined in the Λ representation, from ab initio CI calculations using non-empirical pseudopotentials and extensive orbital basis sets. Avoided crossings with states correlated to higher excited configurations, e.g. 5s, 5p and 3d for Ar*2 and 6s, 6p and 4d for Kr*2 are also taken into account. The structure of the electronic spectrum of both excimers is interpreted; analysing the nature of the Rydberg MO's and the multiconfigurational wave-functions makes possible the understanding of the character of avoided crossing between Rydberg states of homonuclear rare gases.Les courbes de potentiel adiabatiques de Ar(3p6 1S 0) + Ar* (3p5 4s, 3p5 4p) et de Kr (4p6 1S0) + Kr* (4p5 5s, 4p5 5p) sont déterminées en représentation Λ, par des calculs d'IC ab initio mettant en oeuvre des pseudopotentiels non empiriques et utilisant des bases d'orbitales étendues. Les croisements évités, avec des états corrélés à des configurations plus excitées, plus précisément 5s, 5p et 3d pour Ar*2, 6s, 6p et 4d pour Kr* 2 sont également pris en compte. L'analyse de la nature des OM Rydberg et des fonctions d'onde multiconfigurationnelles permet d'interpréter la structure du spectre électronique de ces deux excimères et de comprendre le caractère des croisements évités entre états Rydberg des gaz rares homonucléaires
A pseudopotential study of molecular spectroscopy in rare gas matrices: absorption of NO in argon
We present a pseudopotential method to study the absorption spectroscopy
of NO in an argon matrix modeled by a large albeit finite cluster.
The excited states of NO are described with the virtual orbitals of
a NO+ Hartree-Fock calculation plus a core-polarization operator
to account for the electron-NO+ correlation.
The
argon atoms of the matrix are replaced by
pseudopotentials for the repulsive contributions and core-polarization
operators to account for matrix polarization and
correlation with the excited electron. The model is shown to account for
the matrix-induced transition shifts and also for the cut-off of
the Rydberg series for n > 3 reported in absorption experiments from the
ground state
Theoretical study of the electronic structure of the low-lying states of the Li 2 H molecule
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