Incoming links: Precession
Besides the angular momentum in each direction, we also have the total angular momentum:
Then you have to understand what each one of those does to the each atomic orbital:
- total angular momentum: determined by the azimuthal quantum number
- angular momentum in one direction ( by convention): determined by the magnetic quantum number
There is an uncertainty principle between the x, y and z angular momentums, we can only measure one of them with certainty at a time. Video 1. "Quantum Mechanics 7a - Angular Momentum I by ViaScience (2013)" justifies this intuitively by mentioning that this is analogous to precession: if you try to measure electrons e.g. with the Zeeman effect the precess on the other directions which you end up modifing.
TODO experiment. Likely Zeeman effect.
Quantum Mechanics 7a - Angular Momentum I by ViaScience (2013)
Source. Ciro Santilli once visited the chemistry department of a world leading university, and the chemists there were obsessed with NMR. They had small benchtop NMR machines. They had larger machines. They had a room full of huge machines. They had them in corridors and on desk tops. Chemists really love that stuff. More precisely, these are used for NMR spectroscopy, which helps identify what a sample is made of.
Basically measures the concentration of certain isotopes in a region of space.
Introduction to NMR by Allery Chemistry
. Source. - only works with an odd number of nucleons
- apply strong magnetic field, this separates the energy of up and down spins. Most spins align with field.
- send radio waves into sample to make nucleons go to upper energy level. We can see that the energy difference is small since we are talking about radio waves, low frequency.
- when nucleon goes back down, it re-emits radio waves, and we detect that. TODO: how do we not get that confused with the input wave, which is presumably at the same frequency? It appears to send pulses, and then wait for the response.
How to Prepare and Run a NMR Sample by University of Bath (2017)
Source. This is a more direct howto, cool to see. Uses a Bruker Corporation 300. They have a robotic arm add-on. Shows spectrum on computer screen at the end. Shame no molecule identification after that!Proton Nuclear Magnetic Resonance by Royal Society Of Chemistry (2008)
Source. This video has the merit of showing real equipment usage, including sample preparation.
Says clearly that NMR is the most important way to identify organic compounds.
- youtu.be/uNM801B9Y84?t=41 lists some of the most common targets, including hydrogen and carbon-13
- youtu.be/uNM801B9Y84?t=124 ethanol example
- youtu.be/uNM801B9Y84?t=251 they use solvents where all protium is replaced by deuterium to not affect results. Genius.
- youtu.be/uNM801B9Y84?t=354 usually they do 16 radio wave pulses