I'm trying to teach myself the theory behind NMR spectroscopy, but I am having some trouble with some pchem/physics concepts that I have never seen before. The chapter I am currently on talks about the quantization of nuclear angular momentum. What I don't understand is, what is the difference between spin number (I) and nuclear spin angular momentum which my book gives as P=h/2pi (I(I+1))^1/2 I have looked up what nuclear spin number (I) means on some physics websites and they state that I is the total angular momentum of the nuclei so I don't really understand what P really is if I is the total angular momentum of the nuclei. Another term they talk about in the chapter is quantum number m_I (is this almost the same thing as the quantum number m_s for the electron?). Given a magnetic field of strength B (in the z direction)a magnetic moment u would have an energy U given by U=-u.B=-u_zB where u_z is the z component of u. They then go on to show that the energy is given by U=-y(h/2pi)m_IB (y is the magnetogyric ratio) and state that there are 2I+1 values for m_I. Could someone please explain P, I, and m_I ?? sorry for the equations, I don't know how to use latex.