Molecular beams magnetic resonance

A few Van der Waals complexes have been observed using the analogous teclmique of molecular beam magnetic resonance, in which the molecules are focused using a magnetic rather than an electric field. 

The most important examples of 2S states to be described in this book are CO+, where there is no nuclear hyperfine coupling in the main isotopomer, CN, which has 14N hyperfine interaction, and the Hj ion. A number of different 3E states are described, with and without hyperfine coupling. A particularly important and interesting example is N2 in its A 3ZU excited state, studied by De Santis, Lurio, Miller and Freund [19] using molecular beam magnetic resonance. The details are described in chapter 8 the only aspect to be mentioned here is that in a homonuclear molecule like N2, the individual nuclear spins (1 = 1 for 14N) are coupled to form a total spin, It, which in this case takes the values 2, 1 and 0. The hyperfine Hamiltonian terms are then written in terms of the appropriate value of h As we have already mentioned, the presence of one or more quadrupolar nuclei will give rise to electric quadrupole hyperfine interaction the theory is essentially the same as that already presented for1 + states. 

Molecular beam magnetic resonance of closed shell molecules... 

H2, D2 and HD in their X E+ ground states (a) Principles of molecular beam magnetic resonance... 

Figure 8.1. Principles of magnetic state selection and molecular beam magnetic resonance.

We turn now to the corresponding studies of the isotopic species D2 and HD. The deuterium nucleus has spin Id equal to 1, so that the two equivalent deuterium nuclei in D2 have their spins coupled to give total nuclear spin / equal to 2, 1 or 0. The states with / equal to 2 or 0 correspond to ortho-D2, whilst that with / equal to 1 is known as para-T>2. The molecular beam magnetic resonance studies have been performed on para-D2, in the. 1 = 1 rotational level. Formally, therefore, the effective Hamiltonian is the same as that described above for experimental studies of ortho-H2, also in the J = 1 rotational level. There is one extremely important difference, however, in that the... 

We have described the principles and experimental techniques involved in the molecular beam magnetic resonance studies of H2 and its deuterium isotopes. We have shown... 

We calculate the effects of the Hamiltonian (8.105) on these zeroth-order states using perturbation theory. This is exactly the same procedure as that which we used to construct the effective Hamiltonian in chapter 7. Our objective here is to formulate the terms in the effective Hamiltonian which describe the nuclear spin-rotation interaction and the susceptibility and chemical shift terms in the Zeeman Hamiltonian. We deal with them in much more detail at this point so that we can interpret the measurements on closed shell molecules by molecular beam magnetic resonance. The first-order corrections of the perturbation Hamiltonian are readily calculated to be... 

The rotational and Zeeman perturbation Hamiltonian (X) to the electronic eigenstates was given in equation (8.105). It did not, however, contain terms which describe the interaction effects arising from nuclear spin. These are of primary importance in molecular beam magnetic resonance studies, so we must now extend our treatment and, in particular, demonstrate the origin of the terms in the effective Hamiltonian already employed to analyse the spectra. Again the treatment will apply to any molecule, but we shall subsequently restrict attention to diatomic systems. 

Many other diatomic molecules with1X ground states have been studied by molecular beam magnetic resonance. Where magnetic nuclei are present, magnetic focusing is based upon the nuclear Zeeman effects. This is the case with 15N2 for which the... 

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