Equation (4) is an exact result that applies to a specific quantum mechanical pr
ID: 1770819 • Letter: E
Question
Equation (4) is an exact result that applies to a specific quantum mechanical problem. We then applied that result to the dye absorption experiment. Several of the assumptions required to obtain equation (5) for the dyes from equation (4) appeared drastic, but the most important thing we have ignored was not mentioned: the presence of the solvent. The solvent has two major effects. First, because each dye molecule is surrounded by a different arrangement of solvent molecules, the molecules all absorb at slightly different wavelengths, and the sharp absorption peak that would be expected for an isolated dye molecule spreads into a broad band (in this case, tens of nanometers wide). Second, if the interactions of the solvent with the initial and final states are different, the position of the peak can be shifted to higher or lower wavelengths. Such shifts are most important when the dipole moment of the absorbing molecule changes between the initial and final states, " Do you expect that the dipole moment will change a lot upon absorption, so that strong differences can be expected between gas and solution phase spectra? Comment on what would happen to the absorption maxima if the solvent were to stabilize the excited state more than the ground state and vice versa. Short of measuring gas phase spectraExplanation / Answer
We know when electromagnetic radiation is absorbed by an atom or the molecule, the energy of the radiation changes the state of the atom or molecule. In gaseous state, the number of states is discrete for a specific energy range in gaseous state. But in liquids or solids, there are continuous density of states distribution and often possess continuous energy bands. If a substance has to change its energy it must go through the absorption of a photon. Hence we can say that the dipole moment will change a lot so that strong difference can be expected between the gas and solution phase spectra.
If the solvent were to stabilize excited state more than the ground state the absorption maxima will be very high because of the absorption of more photon.
In the vice versa case, the place where the absorption maxima occurred will turn to the minima.
Solvent has a crucial effect in forming spectra. So without using the solvent experiment is meaning less.
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