IR-Laser Spectroscopy of Free Radicals and Open-Shell Molecular Ions

Abstract

Infrared laser spectroscopy of open shell molecules can take advantage of the Zeeman effect for both modulating and tuning of the corresponding transitions into resonance with a fixed frequency laser line. Thus it is very similar to EPR, however the tuning range is much smaller than the transition frequency, which can be either the rotational or the vibrational energy of a molecule. This method, which is well known as “Laser Magnetic Resonance” (LMR), has first been developed and brought to perfection by K.M. EVENSON and coworkers /l/. They achieved sensitivies down to 10 diatomic molecules per cm in the far infrared region for pure rotational molecular transitions. An essential feature of EVENSON’s LMR system is the intracavity arrangement, i.e. the absorption cell, where the shortlived species are generated by a chemical reaction, is incorporated in the laser cavity. The high sensitivity of this intracavity setup can be understood in terms of the increased effective pathlength through the sample and the non- linearity of the laser system, as has been pointed by H.E.RADFORD et al. /2/.

ded

This paper is dedicated to Prof. Dr. H.G. Kah1e, my previous supervisor, for the occasion of his 60^th birthday.