3 - magnetic moment of the nucleus /previously parallel with the outer magnetic field /- it pays for the nucleus from a small excessive population of nuclei with the lower energy, otherwise the +1/2 and - 1/2 spin populations are almost equal and almost well balanced/ flips due to absorbed quantum of radiofrequency radiation against direction of the applied outer magnetic field to achieve equality of both populations.

NMR spectra are obtained via resonance effects rather than discrete absorption phenomena. Although energy diagrams are often used to simplify explanation.

1 & 2) Effectively the same question. No - spin angular momentum is quantised not classical, the Larmor precession frequency is constant for a given nucleus in a magnetic field of a given strength

3) Also no; the interaction of a radiofrequency pulse does not result in any discrete absorptive transition of individual nuclei.

When exposed to a magnetic field, particles possessing spin, precess with or against the applied magnetic field at the Larmor frequency. This splits the usually degenerate spin states and causes a small excess in the population of the lower energy spin state. Resulting in a small buk magnetisation of the sample in the direction of the magnetic field. All of the different spinning nuclei will be out of phase.

When irradiated at a 90 degree angle to the large magnetic field, the nuclei resonate with the magnetic component of the radio frequency pulse at the respective Larmor frequency causing the bulk magnetisation to rotate transverse to the magnetic field. This net rotating magnetic moment induces a current in the dectector coil resulting in a free induction decay curve that is converted into a spectrum.

Aitawade,

Please, find the answer to your question and any others which might pop up in the following site

---http://www.cis.rit.edu/htbooks/nmr/

By Dr. Joseph P. Hornak

Good luck