(long) question - Raman, IR spectroscopy; virtual energy states, light; heat

[Jacksono]

I'm confused about what is going on theoretically with Raman, and light in general, wrt photon absorption, annihilation, and re-emission; I don't have the math background to understand Fourier transform, of anything past simple algebra anymore, but would like to at least have a decent qualitative understanding.

1. I don't understand what is meant by "virtual" energy states.

2. I’m also confused with the difference between an electron needing a photon of a specific energy to move to a higher quantum level, and then re-emitting a new photon as it de-excites to a lower n-level, vs if a photon entering a Raman spectrometer is absorbed that there are some other kind of energy states that are not coming from quantum levels for electrons ('virtual'?), yet the atoms are emitting energies in the form of photons - it's not making sense for me that these photons are not coming from a de-exciting electron making a quantum jump down, that is, they are emitting photons of say IR but these aren’t coming from a specific quantum leap down from one n-level to another (?)

3. Another thing that I'm having trouble understanding, related but different, is how IR photons can be described also as heat - something is lost here on me - I think of heat as a transfer of vibrational motion on the atomic level - how is infrared radiation also “heat”, per se? How does heat, or say a photon of IR frequency, "heat" something up - or also, if something is emitting IR photons, is that energy coming from de-excitation of electrons from the object's atoms as they fall back to ground state? (Perhaps there are different definitions of ‘heat’ and I need that cleared up.)

Can photons be emitted from different aspects of an atom, or rather, groups of atoms, and not just from electron quantum transitions? Am I confusing different sources of energy transfer - ie, photon absorption vs. say electrical transfer of energy? If a CCD is detecting a photon, which can also be described as a wave, what are the possible sources or originations of that photon ?

I also don’t understand yet fluorescence and how that works with getting in the way of Raman emission.

The word "scattering" I'm guessing means that photons are scattered, but the source of these photons I don't understand, and again, virtual energy states that arise from inelastic scattering - what is that - are these energy states unrelated to electron quantum transitions, that come from phonon vibrations/polarizations? I think I'm hung up on thinking that all photons must come from electrons in atoms being emitted after absorbing photons from another source.

I seem to think that if a photon say of IR is emitted from a depolarizing chunk of matter, that IR photon has to have enough energy to collide with an electron in an atom say in a CCD which moves that electron to another quantum state, etc.

I seem to have forgotten also how IR spectroscopy really works, as well, qualitatively - is this also virtual (whatever that means) transition emission?

Thanks in advance for any info anyone can help enlighten me with, -Jackson. oreilly.jackson@gmail.com

 

[jbsteele]

1. Virtual energy states refer to energy levels that exist due to the interaction between particles, but are not actually observable as distinct energy levels in a system. These virtual energy states can be used to describe the behavior of particles, and they can be used to calculate the probability of certain interactions occurring. 2. When a photon is absorbed by an atom, it can be absorbed by an electron causing it to move from one quantum energy level to another (which is the quantum jump mentioned above). This process is known as "photo-excitation", and it is the basis of many spectroscopy techniques, including Raman spectroscopy. However, when a photon enters a Raman spectrometer, it can also be absorbed by the molecules in the sample and cause them to vibrate in a way that is not related to any particular quantum level. This vibration is known as "inelastic scattering", and the resulting energy states are referred to as "virtual" energy states. These virtual energy states can then lead to the emission of photons at different wavelengths, which can be detected by a CCD or other detector. 3. Infrared radiation is often described as heat because it is a form of electromagnetic radiation that has a long enough wavelength to be felt as thermal energy by the human body. This thermal energy can then be used to heat up objects, which will then emit infrared radiation in response. This emitted infrared radiation is not necessarily coming from electrons making quantum jumps, but rather from the collective vibration of the atoms in the object. 4. Photons can indeed be emitted from different aspects of an atom, such as vibrations, transitions, and even nuclear decay. The source of these photons can be determined by looking at the wavelength of the photons. For example, photons with a wavelength in the infrared range are usually generated by vibrational transitions of molecules, while those with a shorter wavelength are generated by electronic transitions. 5. Fluorescence occurs when a molecule absorbs a photon of light and then re-emits it at a lower energy level. This lower energy level is usually in the visible range, so it is possible that this fluorescence could interfere with the detection of Raman emission.