Aspects of free radical spectroscopy

Abstract

Techniques for the computer solution to the eigenvalue problem for the effective Hamiltonian describing the rotational levels of asymmetric top free radicals in the presence of an external magnetic field are presented. They are used to perform the analysis of experimentally observed data for the H02 radical and derive refined values for the major parameters appearing in the effective Hamiltonian describing the ground state of the molecule.
The detailed form of the effective spin-rotation Hamiltonian including its centrifugal distortion correction for an asymmetric top free radical is derived and a form suitable for the empirical fitting of experimentally observed spectra is discussed. It is shown that for molecules of lower than orthorhombic symmetry there are fewer determinable quadratic spin-rotation parameters than have been used previously. Similar indeterminacies exist among the quartic terms and the case of a molecule of orthorhombic symmetry is discussed in detail. The results are applied to the available experimental data on the spin-rotation splittings of the H02, NH2 and N02 radicals in their ground vibronic states. The observation of magnetic dipole transitions between the fine structure states of X-2 π SeH by laser magnetic resonance spectroscopy is described. The spectra are analysed in terms of the effective Hamiltonian for a 2π electronic state and refined values for several of the major molecular parameters determined.

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