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Different regions of the electromagnetic spectrum interact differently with matter:

  • Microwave radiation can induce molecular rotation.

  • Infrared radiation can induce molecular vibration.

  • Visible and ultraviolet light can induce electron excitation.

  • X-rays and gamma rays can induce ionization.

Is there any activity specific only to radio waves? I kept on thinking how radio waves are used in NMR but I don't know what to call it.

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    $\begingroup$ Radio waves are weak; they can't do anything of the above, which leaves us with your suggestion on NMR. $\endgroup$ Commented Sep 4, 2019 at 15:25
  • $\begingroup$ While NMR is in principle the energy range of radio waves, actual instruments do not use interaction with electromagnetic radiation, but only induce and detect near-field magnetic interactions. There are no actual photons emitted or absorbed by your sample. The advantage is of course that you can create and perfectly detect (phase sensitive!) any kind of waveform. $\endgroup$
    – Karl
    Commented Sep 4, 2019 at 20:34
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    $\begingroup$ "actual instruments do not use interaction with electromagnetic radiation, but only induce and detect near-field magnetic interactions." Certainly NMR is not like UV-Vis, but pray what is the job of the radio-frequency transmitter then? $\endgroup$
    – ACR
    Commented Sep 7, 2019 at 14:36
  • $\begingroup$ @M.Farooq The "transmitter" powers the pulsed radio frequency $B_1$ field. It never decouples from the probe coil to become electromagnetic radiation, i.e. actual photons. Here onlinelibrary.wiley.com/doi/abs/10.1002/… is the classical text on the matter. $\endgroup$
    – Karl
    Commented Sep 8, 2019 at 22:06
  • $\begingroup$ @Karl, the article is worthwhile and they correctly suggest that the concept of radio wave absorption and emission is rampant. However, no one can generate an isolated oscillating magnetic field without an accompanying electric field in a RF coil. This pulse is electromagnetic in nature. See RF coils - for non physicists in the same journal ncbi.nlm.nih.gov/pmc/articles/PMC6175221 $\endgroup$
    – ACR
    Commented Sep 8, 2019 at 23:47

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This is a bit of a stretch, but the Zeeman and Stark effects are linked to radio frequencies, in that line splitting of a visible spectral frequency (~10^15 Hz) can give rise to a beat-frequency in the RF. Your answer of NMR, though, is more applicable. The most general term for precession in a magnetic field is Larmor precession.

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Radio waves $10^4$ to $10^{11}$ Hz are not that innocent as is commonly purported. Long time ago there was an demonstration that radio waves of certain frequency can decompose salt water into hydrogen and oxygen (and ignite). There was an article in Popular Mechanics. No other type of radiation can cause this effect. See the video of burning here Burning salt water. John was trying to cure his cancer but died at young age in early 60s.

Radiofrequency is routinely used to generate argon plasma for atomic spectroscopy (which heats it up to the temperature of the Sun). One spectroscopist had jokingly mentioned that a senior advised him not to work with this equipment because it may make you sterile.

For the information of some readers who think microwaves and radiowaves are different, radio waves include microwaves. Microwaves are basically high frequency radio waves. http://wifiinschools.org.uk/15.html

Both microwaves and radiowaves can easily generate plasmas and atomic spectroscopy can be done with both.

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    $\begingroup$ This video and the now missing self-published journal report are highly suspect. Nowhere do they mention the intensity of the radiation required (while seeming to imply that they get more energy out than put in). Yes, high intensity RF can generate plasmas and possibly other effects (the 1kW or so of RF power in a microwave can generate plasma easily) but this is hardly more impressive than being burned by the IR from a domestic toaster. $\endgroup$
    – matt_black
    Commented Sep 6, 2019 at 15:30
  • $\begingroup$ $10^{11}$ is deep in the microwave regime. A hundred Gigahertz. Your kitchen microwave oven runs at 2.45 GHz. And a plasma is electrically conductive, and you need an electrical discharge to start it. $\endgroup$
    – Karl
    Commented Sep 6, 2019 at 19:35
  • $\begingroup$ en.wikipedia.org/wiki/Rotational_spectroscopy , done in the tens of GHz. $\endgroup$
    – Karl
    Commented Sep 6, 2019 at 19:44
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    $\begingroup$ Radio waves do not generate plasma, you can heat and thereby keep alive a plasma with high power radio waves. Or you can generate an electric spark with radio waves, if you have a conducting antenna. Youre leaving out the central pieces of your statements. $\endgroup$
    – Karl
    Commented Sep 8, 2019 at 22:25
  • $\begingroup$ No need to split hairs here. It might be better if you write a separate detail reply to the original query. In the ICP torch, there is an initial seeding to create ions in the argon gas, and the RF coil transmits power (inductive coupling) and creates a sustained plasma. $\endgroup$
    – ACR
    Commented Sep 8, 2019 at 23:24
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Radio waves have a longer wavelength than infrared radiation and is classified between 3Hz and 300MHz frequencies. Due to its lower energy/longer wavelength, radio waves are able to penetrate deeper than higher energy radiation. For example, the skin depth is a function of frequency: $$\delta = \sqrt{\frac{2 \rho}{\omega \mu}}$$ where $\rho$ is the conductivity, $\omega$ is the angular frequency, and $\mu$ is the magnetic permeability. As the frequency increases, the skin depth decreases. This is the reason AM and FM radio (in the kHz range) is able to travel very large distances, while your standard 2.4GHz wireless router has poor connectivity through walls.

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Radiofrequency energy possesses quite important heating capabilities. What matters is not the energy hf carried by the wave, but rather its intensity and focusing.

Induction heating generators, with power ratings from a few kilowatts to several hundred kilowatts and running in the range from a few kilohertz to several hundred kilohertz are routinely used in the metal industry for heat treatment processes, such as induction hardening, brazing, or forging. The intense heating effect owes its efficacy to the induced parasitic currents flowing within a relatively shallow "skin" region in the heated material.

In addition, a dielectric heating effect may be obtained by using radiofrequency generators in the megahertz range for myriad processes such as adhesive bonding, plastic forming, wood drying, and even radiothermal healing in medicine.

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Radiofrequencies can induce changes in proton and other nuclei energy levels in a magnetic field. Guess what? the entire Earth is in a magnetic field. All those protons, phosphorus atoms, C-13 atoms, etc. are dithering when exposed to radiowaves. Are there natural radiowaves? Yes, in blackbody radiation. Measureable? Who knows but Gravity waves were recently not detectable.

A Story: Years ago when my children were about 7 years old [they are now 50] [and my hearing had a wider high frequency range] We were at our cottage in the Adirondack Mountains of NY. The Adirondacks then and still do have minimal light pollution and the Perseid Meteor shower coincided with a new Moon. We spread blankets in a clearing surrounded by trees and underbrush, lay down and looked up to Blackness and some stars. After several minutes someone said "I saw one!" then "Me too, Me too". Every minute or so a large meteor flashed overhead. As our vision accommodated the sky became full of tiny meteoric flashes with occasional large trails; it was almost magical! Suddenly one of the kids said "I HEARD that one"! We were a little concerned about occasional rustling in the woods thinking animals were approaching to pounce. We said NO they are too high up to hear. SSSSH lets listen. We soon realized that there was sound coinciding with the meteors; We could hear them in real time. The perfect combination of darkness and silence. We still talk about it today.

Some thirty years later, browsing a Nature journal, I encountered an article claiming that meteors emitted radio waves that could be absorbed by dry plant matter and converted into sound enabling meteors to be heard as they are seen. Unfortunately I did not copy the article.

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