Orientation selection in pulse EPR

A resonator can be considered as a bandpass filter. The exeitation bandwidth Avis determined by the resonator quality factor and is given by Qi = v/Av. For example, at X-band with v= 9.8 GHz and 100, a total bandwidth of approximately 100 MHz or 3.5 mT is exeited. In addition to the resonator, the excitation width of the m.w. pulse needs to be considered. With the maximum available microwave power and value the B field strength is sueh that a n/2-pulse requires typically 10 ns (a rectangular pulse of width L has a sine function in the frequeney domain with a full width at half height of s3.79/(23iL) Hz). 

The resulting exeitation bandwidth may be enough to excite the complete spectrum of an organic radical at X-band, but typically only excites a narrow region of the spectrum from a transition metal complex. Consider for example the EPR spectrum of Cob(II)alamin with g-values of g = 2.272, g2 = 2.230, g, = 2.004 

JEFFREY HARMER, GEORGE MITRIKAS, and ARTHUR SCHWEIGER 

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