Why would the first excited state (A) transitions not be observed in UV-Vis Spectra for I2 ?
I2 have one single bond. This is a covalent molecule.
there are no pi bond. so there are no chances the pi - pi* transition.
But in I2, there are sigma - sigma* transition occurs.
the energy gap between sigma - sigma* is high in compare to pi - pi* gap.
During UV-Vis study the monochromatic light used can not excite the electron from sigma to sogma* due to higher energy gap.
Hence in UV-Vis spectra of I2, there are no peak or band.
Hence first excited state (A) transitions not be observed in UV-Vis Spectra for I2.
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