A VERSATILE PULSED X-BAND ENDOR SPECTROMETER

A versatile high power X-band (8.5-9.5 GHz) pulsed EPR/ENDOR (electron -nuclear double resonance) spectrometer which can generate hundreds of microwave (MW) and rf pulses is described. The pulse programmer is co nstructed from a word generator with 32 channels and 4 ns resolution, coupled to five digital delay,generators which can produce a total of ten pulses with a resolution better than 1 ns. The spectrometer contai ns two MW and two rf channels that allow independent variation of the frequency, amplitude, and phase of the MW and rf pulses. The ENDOR pro be head is based on a bridged loop gap (BLG) resonator, coupling is ac hieved via a coupling loop connected to a waveguide, and the rf coil s erves as a MW shield as well. The adjustment of the coupling is done b y an up/down motion of the of the resonator assembly with respect to t he fixed coupling loop. A flexible and user friendly data acquisition program written in C++ (Borland version 4.5), which uses the Windows-9 5 Multiple Document Interface (MDI) programming model, was developed t o run the spectrometer. This program allows easy programming of any pu lse sequence with sophisticated phase cycling. The performance of the spectrometer is demonstrated by two experiments. The first is the trip le resonance hyperfine-selective (HS) ENDOR experiment carried out on a frozen solution of the copper protein laccase. The second is the two -dimensional hyperfine-ENDOR (HYEND) correlation experiment performed on a single crystal of gamma-irradiated malonic acid. (C) 1998 America n Institute of Physics. [S0034-6748(98)02908-6]