Modulation depth factor

Suggest an explanation why S-band ESEEM spectroscopy sometimes give better signals than at X-band, especially for weakly coupled nuclei [R.B. Clarkson, D.R. Brown, J.B. Cornelius, H.C. Crookham Pure Appl. Chem. 64, 893 (1992)]. Hint The modulation depth factor... 

It is customary to introduce a modulation depth factor k = A la Ip and to use the angular frequency ty = 27tv in the equations for the time dependence of the ESEEM signal. 

At Q band it was shown that for a moderate decrease of the bandwidth or turning angle of the pump pulse the recovery of the DEER echo amplitude is stronger than the loss in modulation depth. ° As a result, optimal SNR in Gd(iii)-nitroxide DEER is achieved at a nominal flip angle for the pump pulse between 2n/3 and nil rather than rt. A stronger sensitivity improvement is characteristic for complexes with weak ZFS, while the effect is not so dramatic for complexes with relatively strong ZFS. For instance for Gd(m)-DOTA (D 500 MHz) the SNR improves by about a factor of 2.5-3.0, which results in almost an order of magnitude reduction of the measurement time. For a Gd(m)-DTPA complex D 1500 MHz) only about 40-50% of SNR improvement was observed. 

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