Offset between absorption and emission spectra
Although atoms are said to emit and absorb emr at only very specific frequencies (ie. Hydrogens Balmer series), observations contradict this. And show that there is an offset between the absorbed and re emitted light. Which seems counter-intuitive, given the assumption that the atoms resonant frequency should respond to and produce the same frequencies of light. Not two slightly different frequencies
To explain this one must realise that the each of atoms resonant frequencies is actually a range of resonant frequencies clustered around a single frequency. And described in graph form by a bell curve. And confirmed also in spectra by the observed width of the emission/absorption line. With the peak amplitude of resonant wavelength being at the Center of the spectral line.
In other words at each resonant frequency of the atom, as illustrated by the width of the observed spectral line of the atom, the atom actually has a range of resonant frequencies clustered around that specific frequency. And described in graph form by a bell curve with the maximum frequency being at the peak of the curve at the Center of the observed spectral line.
Taking this into account one can then explain how the offset between emission and absorption occurs. Because although the frequency range of the atoms resonant frequency is a uniform bell curve above and below the center of that particular resonant frequency. The input and output energies are different on either side of the Center.
The Higher frequency side of the bell curve will have more input energy than the lower frequency side seeing as higher frequencies have more energy. Thus the absorption spectral line appears to be stronger on the higher frequency side of the curve. And conversely when that same absorbed energy is emitted again by the atom, the lower frequencies appear brighter. Because although a larger part of the input energy to the atom was from the higher side of the frequency bell curve of the atom, the total emitted energy is split equally between both hi and low frequency sides of the resonant frequency bell curve. Resulting in a slightly lower frequency emission line
This assumption is based on the fact that the atoms resonant frequency is centered on a single hypothetical wavelength. When absorbing equal frequencies of energy on either side of the bell curve it becomes obvious the higher frequency side receives more energy and appears brighter in the observed spectra. But when this energy is emitted equally between lower and higher frequencies ...the lower frequency side of the bell curve appears brighter. Thus shifting the emitted spectral line slightly to a longer spectral wavelength. As observed.
