86
Q.-F. Zhang et al. / Journal of Molecular Structure 525 (2000) 79–86
atom by heavier W atom allows more efficient spin–
orbital coupling and ionization/geminate recombina-
tion between the W and Se atoms than between the
Mo and Se atoms. However, non-linear refraction
effects of 1 and 2 are not influenced by substitution
of the center atom. Based on our previous results from
the theoretical analyses, the reason may be that an
intense charge transfer may not necessarily give rise
to a large refractive index [27].
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Acknowledgements
Acknowledgement is made to the research funds
from the National Science Foundation (No.
29631040) and Education Department of China.