Aller au contenu  Aller au menu principal  Aller à la recherche

bandeau kit ICB

Laboratoire Interdisciplinaire Carnot de Bourgogne

Spectroscopie dans un état électronique dégénéré

TRANSITION-METAL HEXAFLUORIDES, HEXACARBONYLS AND OTHER MOLECULAR OPEN-SHELL SYSTEMS

 

The transition metal hexafluorides form a very interesting group of molecules, since they are the only compounds of these heavy elements with substantial vapor pressures at room temperature. This implies several industrial applications, such as isotope separation processes (especially with UF6, NpF6 and PuF6) or chemical vapor deposition of thin metal layers on a substrate (WF6, MoF6 for integrated circuits ; ReF6, IrF6 for anti-corrosion layers).

Among these molecules, there is a very interesting group which is traditionally called "colored hexafluorides". They are caracterized by the fact that they have an incomplete electronic subshell. This leads to low energy electronic levels, corresponding to transitions in the visible or near infrared regions (see figure below). Some of the "colored hexafluorides" also have the property of possessing an odd number of electrons (TcF6, RhF6, ReF6, IrF6, NpF6, AmF6).

 

 Transitions

 Difference between the absorption spectra of XY6 closed- and open-shell systems.

 

Their specificities of these molecules are that :

  • They are open-shell systems, and their spectroscopy is similar to that of molecular ions.
  • Their study is simpler than that of ions since it is easier to obtain a high density with molecules than with ions.
  • They are very reactive (hygroscopic, ...).
  • We have already recorded and analyzed low-resolution absorption and Raman spectra of IrF6, OsF6 and WF6 and obtained low-resolution absorption spectra of PtF6.

High-resolution spectra of WF6 and ReF6 using infrared spectroscopy (Fourier transform and diode laser) in a supersonic expansion jet were obtained in the Group of Professor Martin Quack (LPC-ETH Zürich). The analysis of the spectra of ReF6 requires a tensorial formalism adapted to rovibronic couplings and to the presence of half-integer angular momenta in octahedral symmetry. This work is still in progress

Transition-metal hexacarbonyls (Cr(CO)6, Mo(CO)6, W(CO)6, ...) are also interesting octahedral systems although this familly of molecules is much smaller that that of hexafluorides. There also exist an open-shell hexacarbonyl system with an odd number of electrons, namely V(CO)6 (vanadium hexacarbonyl).

Such studies could be extended to other open-shell systems like ReOF4 or to molecular ions or radicals of interest in astrophysics (CH3O, ...) or atmospherics physics.

 

Table of the known and expected hexafluorides.

TabHexa

 

  • Example 1 : The NIR-Visible-UV absorption spectrum of some colored hexafluorides

Hexa abs

Spectra from M. Rotger and V. Boudon. The letters (a, b, c, ...) indicate the different electronic states.

 

  • Example 2 : The NIR-Visible-UV absorption spectrum of IrF6

IrF6 all 

Spectra from M. Rotger and V. Boudon. The letters (a, b, c, ...) indicate the different electronic states (with symmetry in parentheses).

Réference:

Spectroscopy of Hexafluorides with an Odd Number of Electrons: The Vibronic Bands of IrF6,
V. Boudon, M. Rotger and D. Avignant,
Journal of Molecular Spectroscopy175, 327–339 (1996).

 

  • Example 3 : Jet + diode laser high-resolution spectrum in the ν3 band of WF6

The case of a non-degenerate electronic ground state.

WF6nu3

Spectra from V. Boudon, M. Rotger, Y. He, H. Hollenstein, M. Quack and U. Schmitt.

Reference:

High-resolution spectroscopy of the ν3 band of WF6 and ReF6 in a supersonic jet,
V. Boudon, M. Rotger, Y. He, H. Hollenstein, M. Quack and U. Schmitt,
Journal of Chemical Physics, 117, 3196–3207 (2002).

 

  • Example 4 : Jet + FTIR and diode laser high-resolution spectrum in the ν3 band of ReF6

The case of a fourfold degenerate electronic ground state.

ReF6

Spectra from V. Boudon, M. Rotger, Y. He, H. Hollenstein, M. Quack and U. Schmitt.

Reference:

High-resolution spectroscopy of the ν3 band of WF6 and ReF6 in a supersonic jet,
V. Boudon, M. Rotger, Y. He, H. Hollenstein, M. Quack and U. Schmitt,
Journal of Chemical Physics, 117, 3196–3207 (2002).

 

  • Example 5 : Jet + FTIR spectrum in the ν6 band (C-O stretch) of V(CO)6

The case of a threefold degenerate electronic ground state.

VCO6

Spectrum from P. Asselin, L. Manceron and P. Soulard / LADIR, Paris, France. Simulation calculated by Michael Rey.

Reference:

The spectrum of an octahedral molecule in a degenerate electronic state: The ν6 fundamental band of jet-cooled V(CO)6,
M. Rey, V. Boudon, M. Loëte, P. Asselin, P. Soulard and L. Manceron,
Journal of Chemical Physics, 114, 10773-10779 (2001).

 

Suivez-nous : Suivez nous sur Facebook Suivez nous sur Twitter

Contact

  • Responsable:Cette adresse e-mail est protégée contre les robots spammeurs. Vous devez activer le JavaScript pour la visualiser.

Tél: +33-(0)3-80-39-59-17
Fax: +33-(0)3-80-39-59-71
Bureau: D106

cnrs     Logo UTBM small  

Université de Bourgogne