Rabi resonance method
The Rabi method has been developed by Isidor Isaac Rabi technique for the measurement of nuclear spins. The atom is located in a static magnetic field perpendicular to a rotating magnetic field is applied.
Theory
According to classical mechanics the equation of motion of the spins in the magnetic field:
With
In which
- The magnetic moment
- : The magneton
- : The dimensionless Landé factor that reflects environmental effects on the spin
- : The reduced Planck's constant
- : Is the gyromagnetic ratio.
If only the static magnetic field is switched on, to precess at the Larmor frequency of the spin, or angular velocity of the corresponding:
The negative sign is necessary. It means that the spinning J handed rotates when the thumb points in the direction of the magnetic field.
When switching in the rotating reference system with the angular velocity of the rotating magnetic field is obtained, the transformed equation of motion:
Or
If so, then the precession of the static field is removed, the spin precesses in the rotating reference system only to the axis of the magnetic field:
The angular velocity ( Rabi frequency ) of this precession is:
Because the rotating field is perpendicular to the static field, the spin between spin-up and spin-down can move back and forth. By sensing the angular velocity, one can determine the maximum of the spin exchange.
Experiment
The experimental set-up consists of three parts:
- Forward an inhomogeneous magnetic field
- In the center of a uniform magnetic field perpendicular to a rotating magnetic field, and
- Behind another inhomogeneous magnetic field.
The two inhomogeneous magnetic fields act as selectors. The first ( polarizer ) splits the molecular beam into two beams with different spin polarization. One of the two beams ( for example, spin-up ) is selected and fed through the central portion of the test setup. If there rotating magnetic field, the Larmor frequency, high beam density with reverse spin orientation (eg, spin-down ) is generated. This is selected with the rear magnetic field (analyzer). , By scanning the frequency of the maximum intensity of this beam is selected. Thus one finds the Larmor frequency and thus the magnetic moment of the atom.
Application
The magnetic moment of an atom depends on its environment, with his bond in a molecule changes the Landé factor. Thus, the structural configuration of a molecule is indetectable.