Electricity and magnetism

The names and symbols recommended here are in agreement with those recommended by IUPAP [4] and ISO [5J]. 

From a physics course in your past you are probably aware that there is an intimate connection between electricity and magnetism. Let us review a few of the relevant physical principles. 

Remember from Section 2.3 that to tip M off the z axis, so it has a component in the x,y plane, we need an irradiating magnetic field (B[) that oscillates at exactly the precessional frequency of the nuclei of interest and is oriented perpendicular to B0. How are we going to generate such a precessing magnetic field  

---

J. C. Maxwell, A Treatise on Electricity and Magnetism, 2nd ed.. Clarendon Press, Oxford, 1881. 

The central equations of electromagnetic theory are elegantly written in the fonn of four coupled equations for the electric and magnetic fields. These are known as Maxwell s equations. In free space, these equations take the fonn ... 

To this point, we have considered only the radiation field. We now turn to the interaction between the matter and the field. According to classical electromagnetic theory, the force on a particle with charge e due to the electric and magnetic fields is... 

Equation (A2.1.8) turns out to be consistent with die changes of the energy levels measured spectroscopically, so the energy produced by work defined this way is frequently called the spectroscopic energy . Note that the electric and magnetic parts of the equations are now synnnetrical. 

Another powerftil class of instmnientation used to study ion-molecule reactivity is trapping devices. Traps use electric and magnetic fields to store ions for an appreciable length of time, ranging from milliseconds to thousands of seconds. Generally, these devices mn at low pressure and thus can be used to obtain data at pressures well below the range in which flow tubes operate. 

Probing electric and magnetic fields, and the effects induced by them, is of obvious mterest in many areas of science and technology. We considered earlier the influence of such perturbations in a general fashion in section Bl.5.2.2. Here we describe some related experimental measurements and applications. Electric fields act to break hrversion and thus... 

Using the above relationship between the electric and magnetic field amplitudes from equation (Bl.26.15)) ... 

The transport of particles in the plasma is diffusive or convective for the neutrals, whereas the charge carriers move under the influence of the external and internal electric and magnetic fields. The drift velocityv of the charged particles is proportional to the electric field E ... 

Scanning for metastable ions requires adjustment of electric and magnetic fields which can be adjusted individually or in conjunction with each other. If two fields are automatically adjusted at the same time, it is known as linked scanning. It is important to remember that metastable ions are not the product ions m2 but are the ions undergoing fragmentation (precursor ions mj). 

As with a light beam and glass lenses, an ion beam can be directed and focused using electric and magnetic fields, often called lenses by analogy with their optical counterparts. 

The system of electric and magnetic fields or lenses is called the ion optics of the mass spectrometer. Electric lenses correct aberrations in the shape of the ion beam. 

Electric and magnetic fields can be used sequentially to focus the beam of ions. The use of crossed electromagnetic fields is described in the discussion of quadrupoles (Chapter 25). 

Another important property of electric and magnetic fields is their ability to separate ions according to their individual masses (m, mj,. .., m ) or, more strictly, their mass-to-charge ratio (mj/z, raji,. mjz). 

By changing the strengths of the electric and magnetic fields, ions of different m/z values can be focused at just one spot (the collector). 

From the strengths of the electric and magnetic fields, m/z values are obtained. 

In conventional mass spectrometry with electric and magnetic sectors arranged in-hne (see Chapter 26), an ion beam consists of a stream of ions of all m/z values, which is separated into individual m/z values by the magnetic sector before being collected by single-point or multipoint detectors (see Chapters 28 and 29). 

Wien analyzer. A velocity filter with crossed homogeneous electric and magnetic fields for transmitting only ions of a fixed velocity. 

In this discussion we define the x direction to be the direction of propagation of the light waves. This means that the yz plane contains the oscillating electrical and magnetic fields which carry the energy of the radiation. Only the electric field concerns us in scattering. Since the oscillation is periodic in both time t and location x, the electric field can be represented by the equation... 

The transverse modes are labelled TEM , where TEM stands for transverse electric and magnetic (field) m and I are integers that refer to the number of vertical and horizontal... 

---