Molecular beam electric resonance of open shell molecules

Molecular beam electric resonance of open shell molecules 

The years from 1960 to 1975 represented a golden era in the radiofrequency and microwave spectroscopy of open shell diatomic molecules. Molecular beam electric resonance was one of the most important experimental approaches, but microwave, far-infrared and magnetic resonance studies of bulk gaseous samples were equally important and our understanding of these open shell species is derived from a combination of different experimental approaches. In this book we have chosen to organise our descriptions according to the experimental techniques employed, but as with any such scheme, we run the risk, which we wish to avoid, of not connecting the results from different types of experiment in a coherent manner. As we shall see, the OH radical is the example par excellence which illustrates the pitfalls of an approach which is technique-oriented, rather than molecule-oriented. 

Many of the open shell species which have been studied have 2 n ground states and therefore share certain common features in their spectroscopic study. In this section we choose to describe, in some detail, the LiO, NO and OH molecules, all of which have 2 n ground states. The complexity increases, however, partly for reasons intrinsic to the species, and partly because of the increased range of techniques which have 

In terms of single electron configurations, the ground and first excited electronic states of LiO may be written 

We shall calculate the matrix elements of the effective Hamiltonian within the basis of these six primitive states in due course. These states do not, however, have definite parities. Since parity is conserved (except in the presence of an applied electric field), we construct a basis set of six functions, three of each parity type, so that for a given J level we are left with the diagonalisation of 3 x 3 matrices, rather than 6x6. More importantly, we are aiming to understand the electric dipole radio frequency and microwave spectra, and know that transitions must occur between states of opposite parity. 

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Molecular beam electric resonance of open shell molecules [1 511... 

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