[karckoo2005]

1) In trans-1,2-dibenzoylethylene, even though the conjugated C=O group frequency coincides directly with the expected C=C stretching frequency, we would not have expected to observe the latter stretching mode in the infrared spectrum. Why?

2) Explain how photochemical isomerization allows the production of the thermodynamically less stable cis isomer. In other words, why is the trans isomer exclusively converted to the cis isomer during short reaction periods and not vice versa? Is it possible, under these conditions, that the trans and cis isomers are in equilibrium with one another?

[wgmwwggmmwgm]

if there exits  the change of dipolement  during ground-excited state transition,
the infrard spectrum will  display some absorption peak. in your question,the
dibenzoylethylene  is a symmetric molecular ,so ………….maybe, i think.
my English is poor, Forgive me.