SPECTROMETER FOR TIME-RESOLVED 2D-FT ESR

Cornell University, Ithaca NY

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Abstract

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. A pulse FT ESR spectrometer capable of capturing transient events on nanosecond time scales and simultaneously recording slower Kinetics on microsecond to millisecond time scale has not been realized elsewhere. A series of technical developments at ACERT have enabled implementation of such a spectrometer. Such a spectrometer requires very short dead-times, high pulse-sequence repetition rates, a unique timing system capable of updating all pulse sequence parameters on every shot (in a few microseconds), and capturing and processing transient signals at such high rates. Also, the shortest dead-times and the highest sensitivity can be achieved at a higher working frequency. All these components have been developed at ACERT and are being integrated into a unique spectrometer. Recent acquisition by ACERT of a Bruker E500 CW ESR spectrometer made available a 12-inch resistive electromagnet for this project, thereby relieving to some extent the inconvenience of arranging several largely incompatible pulse ESR projects around a few available electromagnets. 2D-ELDOR experiments from X to Ku band will be built around this magnet. The existing electromagnet power supply allows this new spectrometer operation up to Ku band, where high quality 2D-ELDOR was demonstrated. Currently the operation is limited to X-band (based on 8 kW peak power TWTA), but operation at Ku band is also planned. Operation at Ka band is also planned, but has to be combined with PDS spectrometer. The spectrometer will be used with closed-loop flow system to study photo processes under pulse laser illumination and with rapid mixing system to study protein folding. Broadband 8-18 GHz (in five bands) microwave bridge, built in early 2000's, will be used in a modern modified version. Time-resolved operation will be entirely based on a dedicated versatile pulse-programmer with real-time control, ACERT-BN2 or its successor.