Ultrawide band multifrequency high-field EMR technique: A methodology for increasing spectroscopic information

We report methodology that combines an ultrawide band multifrequency microw ave system with technology of high magnetic fields for solving challenging problems in electron magnetic resonance (EMR) spectroscopy. This strategy h as been made possible due to a novel EMR facility operating in an exception ally wide range of microwave frequencies of 24 GHz to 3 THz, at magnetic fi elds up to 17 T, and in the temperature range of 1.6 to 330 K, The basic co nfiguration of the multifrequency system works in a transmission mode and e mploys oversized cylindrical waveguides for routing the microwave power. A wide-band, low-noise, liquid helium cooled (4.2 K) InSb bolometer is used f or signal detection, This approach results in an extremely wide-band perfor mance, thus making it possible to employ a variety of solid-state millimete r and submillimeter microwave sources in combination with a far infrared la ser microwave source for performing multifrequency EMR experiments. A compl exity of resonant structures and related technical problems such as microph onics at high magnetic fields is virtually eliminated. The system is simple , yet sensitive, and has been revealed to be extremely advantageous while s olving such problems as observation of AFMR transitions in spin-ordered sys tems, g-factor resolution enhancement in complex organic radicals, and reso nance signal detection in EMR-silent spin systems having integer spin and l arge zero field splitting. A technical description of the multifrequency hi gh-field EMR facility is presented and results of its performance tests are given, The potential utility of using the multifrequency high-field method ology in EMR studies is illustrated with selected examples of its recent ap plications. (C) 2000 Academic Press.