Also the modern EPR spectrometer is a single-frequency instrument, and its ability to produce spectra depends on the possibility of tuning molecular energy level differences by means of an external static magnetic field of variable strenght. With very few exeptions the resonator has always been a key component of the EPR experiment ever since its inception nearly seven decades ago. The actual spectroscopic experiment also involves a classical, macroscopic resonance phenomenon because the sample is held inside a cavity which is constructed as a single-frequency, fundamental-mode resonator cell whose quality factor insures high radiation energy density at the sample to overcome the intrinsically low concentration sensitivity associated with the detection of molecular energy differences of the order of the thermal energy kT. The word ‘resonance’ in EPR refers to the quantum-mechanical phenomenon of transition between molecular spin energy levels induced by microwave radiation (typically: gigahertz frequency or centimeter wavelength).
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The phenomenon of electron paramagnetic resonance (EPR), or electron spin resonance (ESR), is at the basis of a well established spectroscopy widely used in multiple disciplines including, e.g., physics, chemistry, biology, for the characterization of electronic structure of open-shell systems with electron spin S ≠ 0 –. A detection limit of circa 5 µM HO-tempo in water at 800 MHz is obtained for the present setup, and possibilities for future improvement are discussed. Long, straigth, helical, and helico-toroidal cells are developed and tested with dilute aqueous solutions of spin label hydroxy-tempo. We explore examples of a doublet system, a high-spin system, and an integer-spin system. Theory is developed for coaxial transmission with EPR detection as a function of cell dimensions and materials.
#Bruker epr fitting data generator#
Our source is an arbitrary wave digital signal generator producing an amplitude-modulated sinusoidal microwave in combination with a broadband amplifier for 0.8–2.7 GHz.
#Bruker epr fitting data plus#
We explore the alternative of replacing the narrow-band source plus single-mode resonator with a continuously tunable microwave source plus a non-resonant coaxial transmission cell in an unmodulated external field. Extant and long-standing practice is to use a different spectrometer for each frequency. Most (bio)molecular EPR spectra are determined by a combination of the frequency-dependent electronic Zeeman interaction and a number of frequency-independent interactions, notably, electron spin – nuclear spin interactions and electron spin – electron spin interactions, and unambiguous analysis requires data collection at different frequencies. The X-band spectrometer is the general standard with a frequency in the 9–10 GHz range.
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EPR spectroscopy employs a resonator operating at a single microwave frequency and phase-sensitive detection using modulation of the magnetic field.