THE EFFECT OF VARIABLE ELECTRONIC-TRANSITION MOMENT ON THE EELS INTENSITY DISTRIBUTION WITHIN A VIBRATIONAL PROGRESSION - USE OF THE R-CENTROID APPROXIMATION TO ANALYZE RESULTS FOR THE CO B-X AND O2B'-X TRANSITIONS
M. Kimura et al., THE EFFECT OF VARIABLE ELECTRONIC-TRANSITION MOMENT ON THE EELS INTENSITY DISTRIBUTION WITHIN A VIBRATIONAL PROGRESSION - USE OF THE R-CENTROID APPROXIMATION TO ANALYZE RESULTS FOR THE CO B-X AND O2B'-X TRANSITIONS, Zeitschrift fur Physik. D, Atoms, molecules and clusters, 38(2), 1996, pp. 165-169
The CO B-X and O-2 B'-X transitions are analyzed with the help of ab i
nitio MRD-Cl calculations. In both cases a violation of a well-known r
ule in electron energy loss spectra (EELS) is observed, namely that th
e intensity distribution of vibrational bands is normally independent
of both the scattering angle and the incident electron energy. In both
cases strongly avoided crossings are shown to be responsible for the
unusual appearance of the EELS. The analysis is simplified by making u
se of the R-centroid approximation, which was originally developed to
organize and systematize optical absorption and emission data. It is c
oncluded that a breakdown of the intensity distribution invariance in
EELS should occur for a wide class of transitions in which avoided cro
ssings lead to rapid variations in the electronic transition moment as
a function of internuclear separation.