Vibrational excitation via shape resonances in electron scattering from the NO dimer
Vibrational electron-energy loss spectra of polycrystalline thin films (approx.50 A) of dimerized nitric oxide (i.e., (NO)/sub 2/) have been recorded near 20 K at incident energies of 2,9, and 14 eV. The 2 and 9 eV spectra consist mainly of three vibrational peaks which are the first three members of two unresolved progressions ascribed to in-phase (..nu../sub 1/) and out-of-phase (..nu../sub 5/) vibrations of NO molecules within the dimer. The ''background'' intensity and the broadening of the elastic and energy-loss peaks are believed to result from unresolved multiple losses including vibrations within (NO)/sub 2/ and phonon modes. At incident energies in the range 11--15 eV, a progression of seven vibrational members belonging to the ..nu../sub 1/ and ..nu../sub 5/ modes has been observed. This enhancement in the overtones of the fundamental frequencies is interpreted to arise from the formation of transient (NO)/sup -//sub 2/ states. The electron excitation functions recorded between 0--19 eV reveal the presence of two broad ''humps'' at 11.6 +- 0.2 and 14.2 +- 0.2 eV and a strong maximum near 2 eV. The latter is present in all decay channels including the v = 1, 2, and 3 vibrational states of the ..nu../sub 1/ and ..nu../sub 5/ modes, the ''background'' losses and the elastic peak; but, the broad ''humps'' are exclusively related to vibrational excitation of the ..nu../sub 1/ and ..nu../sub 5/ modes. These two resonances appear to be derived from a splitting, via ''through space'' orbital interaction, of unfilled degenerate NO orbitals. In the 2 eV loss spectra the preponderance of a strong infrared mode (..nu../sub 5/) and the absence of anharmonicity in the vibrational peaks suggests that the vibrational excitation cross sections may be dominated by dipole scattering.
- Research Organization:
- MRC Group in Radiation Sciences, Faculty of Medicine, University of Sherbrooke, Sherbrooke, Quebec, Canada J1H 5N4
- OSTI ID:
- 6661193
- Journal Information:
- J. Chem. Phys.; (United States), Vol. 81:1
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ELECTRON-MOLECULE COLLISIONS
EXCITATION
NITRIC OXIDE
DIMERS
FILMS
VIBRATIONAL STATES
CHALCOGENIDES
COLLISIONS
ELECTRON COLLISIONS
ENERGY LEVELS
ENERGY-LEVEL TRANSITIONS
EXCITED STATES
MOLECULE COLLISIONS
NITROGEN COMPOUNDS
NITROGEN OXIDES
OXIDES
OXYGEN COMPOUNDS
640304* - Atomic
Molecular & Chemical Physics- Collision Phenomena