Question

In Spectroscopy, absorption of radiation energy by a molecule results in the formation of an excited molecule. Given enough time, it would seem that all of the molecules in a smaple would have been excited and no more absorption would occur. Yet in practice we find that the absorbance of a sample at any wavelength remains unchanged with time. Why?

Answer 1

Absorbance of a sample at any wavelength is unchanged with time. It is mainly because once molecules absorbs energy it goes to the excited state, in the next moment it loses energy by collision with a non-excited molecule or with solvent molecules. As a result, energy is transferred to the solvent molecule or to the non-excited molecule. Again, these molecules will absorb energy and will undergo the same course. Hence, the absorbance of the sample remains constant at any wavelength.