Max-Planck-Institut für Bioanorganische Chemie, 45470 Mülheim an der Ruhr, Stiftstr. 34-36, Germany.
J Magn Reson. 2012 Jan;214(1):237-43. doi: 10.1016/j.jmr.2011.11.011. Epub 2011 Nov 30.
We describe a frequency tunable Q-band cavity (34 GHz) designed for CW and pulse Electron Paramagnetic Resonance (EPR) as well as Electron Nuclear Double Resonance (ENDOR) and Electron Electron Double Resonance (ELDOR) experiments. The TE(011) cylindrical resonator is machined either from brass or from graphite (which is subsequently gold plated), to improve the penetration of the 100 kHz field modulation signal. The (self-supporting) ENDOR coil consists of four 0.8mm silver posts at 2.67 mm distance from the cavity center axis, penetrating through the plunger heads. It is very robust and immune to mechanical vibrations. The coil is electrically shielded to enable CW ENDOR experiments with high RF power (500 W). The top plunger of the cavity is movable and allows a frequency tuning of ±2 GHz. In our setup the standard operation frequency is 34.0 GHz. The microwaves are coupled into the resonator through an iris in the cylinder wall and matching is accomplished by a sliding short in the coupling waveguide. Optical excitation of the sample is enabled through slits in the cavity wall (transmission ∼60%). The resonator accepts 3mm o.d. sample tubes. This leads to a favorable sensitivity especially for pulse EPR experiments of low concentration biological samples. The probehead dimensions are compatible with that of Bruker flexline Q-band resonators and it fits perfectly into an Oxford CF935 Helium flow cryostat (4-300 K). It is demonstrated that, due to the relatively large active sample volume (20-30 μl), the described resonator has superior concentration sensitivity as compared to commercial pulse Q-band resonators. The quality factor (Q(L)) of the resonator can be varied between 2600 (critical coupling) and 1300 (over-coupling). The shortest achieved π/2-pulse durations are 20 ns using a 3 W microwave amplifier. ENDOR (RF) π-pulses of 20 μs ((1)H @ 51 MHz) were obtained for a 300 W amplifier and 7 μs using a 2500 W amplifier. Selected applications of the resonator are presented.
我们描述了一个频率可调谐的 Q 波段腔（34GHz），设计用于 CW 和脉冲电子顺磁共振（EPR）以及电子-核双共振（ENDOR）和电子-电子双共振（ELDOR）实验。TE（011）圆柱形谐振器由黄铜或石墨（随后镀金）加工而成，以提高 100kHz 磁场调制信号的穿透性。（自支撑）ENDOR 线圈由四个距离腔轴中心 2.67mm 的 0.8mm 银丝组成，穿过柱塞头。它非常坚固，不易受到机械振动的影响。线圈进行了电屏蔽，以实现具有高射频功率（500W）的 CW ENDOR 实验。腔的顶部柱塞是可移动的，允许频率调谐±2GHz。在我们的设置中，标准操作频率为 34.0GHz。微波通过圆柱壁上的一个光阑耦合到谐振器中，通过耦合波导中的滑动短路来实现匹配。通过腔壁上的狭缝实现样品的光激发（透射率约为 60%）。谐振器接受 3mm 外径的样品管。这导致了特别是对于低浓度生物样品的脉冲 EPR 实验的有利灵敏度。探头头尺寸与 Bruker flexline Q 波段谐振器兼容，并且可以完美地安装在 Oxford CF935 氦气流致冷器（4-300K）中。事实证明，由于相对较大的有效样品体积（20-30μl），与商业脉冲 Q 波段谐振器相比，所描述的谐振器具有更高的浓度灵敏度。谐振器的品质因数（QL）可以在 2600（临界耦合）和 1300（过耦合）之间变化。使用 3W 微波放大器获得的最短实现的π/2 脉冲持续时间为 20ns。使用 300W 放大器获得的 ENDOR（RF）π脉冲持续时间为 20μs（1H@51MHz），使用 2500W 放大器获得的 ENDOR（RF）π脉冲持续时间为 7μs。介绍了谐振器的一些应用。
