Hello.
It is well known that photon is well absorbed to the atom (or ion) if energy difference between two levels are perfectly matched to the photon energy.
What about the case that photon energy is higher than energy level difference? I guess it is a kind of opposite case of multi photon absorption. Is it also effective?
Absorption of a photon occurs only when the quantum energy of the photon perfectly matches the energy gap between the initial and final states. On the other hand, if the photon energy is higher than the energy gap i.e. there is no pair of energy states such that the photon energy can elevate the system from the lower to the upper state, then possibly the matter will be transparent to that incident photon.
Yes, if you apply the Doppler Effect, giving a speed to the atom, or rather additional energy.
If the photon is too energetic the speed of the atom has to go away from the source...
source and atom dethatching allows higher frequency to be absorbed.
There is no other way to make the match...
It depends on the wavelength (energy of photon). For example, the IR of 800nm, it's very low energy and spatial size is quite large to interact with electron so that harmonic (energy matching) is important. But, for high energy photon such as x-ray, its behavior is more like particle so that whenever they interact with electron, they transfer the energy and still having the rest of the energy. People are using this phenomena in EXAFS to investigate the electron structure,
Joon-Gon,
even for gamma photons the absorption has been promoted with the Doppler effect. In such cases the speed has to compesnate the energy of the recoil. The recoil is not present in the Mossbauer effect and in such case no speed and doppler effect is needed for the nuclear recoiless resonance absorption close to 0k in a Crystal.
Thanks everyone! quite kind and detailed answers!
Thus there are several cases in which photon with higher energy than bandgap or difference between two energy levels (energy gap) can be absorbed according to summary in your answers.
1. the case that additional energy (= photon energy - energy gap between two electronic states) can be released to other form of energy such as lattice vibration (we normally call this as material heating maybe.) or kinetic energy to the atoms in gas?
2. if atom's speed is considerable such that Doppler effect can compensate photon energy to exactly harmonically (used this word to include multi-photon absorption) matched to energy gap. In this case temperature of the gas must be quite high like in plasma?
3. If photon energy is so high such that its wavelength is close to some size of the electron. In this case photon plays like role of particle thus particle like collision to the electron in atom is possible to get absorption.
I'm currently interested in laser absorption in gaseous state or atoms in plasma in visible to UV range, 2nd case is only that I have to consider?
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