This note reports a study of the coating of a crystal with `ice' at temperatures below 45 K during single-crystal in-house diffraction experiments when using an open-flow helium cryostat. The `ice' consists mainly of crystalline oxygen and nitrogen. This suggests completely different techniques for avoiding this type of icing compared with water icing. With appropriate choices of crystal mount, crystal position with respect to the nozzle and gas flow conditions, it is possible to avoid detectable condensation. However, sometimes this cannot be achieved in practice (poor diffraction from a smaller crystal, necessity of positioning the crystal in certain orientations to achieve desired data completeness, need to reduce helium consumption etc.). The problem of icing seems to be less common for powder experiments where the laminar gas flow is parallel to the capillary containing the sample, and for synchrotron experiments where the sample is comparatively small and almost continuously rotated, which facilitates the ice covering being removed by the gas flow. This last technique can in principle also be applied to single-crystal X-ray diffraction using laboratory diffractometers – periodic rapid rotation of the crystal can help to minimize any icing, but this technique will not work when the condensation rate is comparable to or faster than one frame of data collection. The coating around a sample crystal reduces the quality of the diffraction data, and the temperature at the sample below the coating may differ significantly from that at the cryostat nozzle reported by the instrument.

中文翻译：

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使用开放式氦低温恒温器进行单晶内部 X 射线衍射实验中的 N2-O2 结冰

本说明报告了在使用开流式氦低温恒温器进行单晶内部衍射实验期间在低于 45 K 的温度下用“冰”涂覆晶体的研究。“冰”主要由结晶氧和氮组成。这表明与水结冰相比，避免这种结冰的技术完全不同。利用适当的晶体安装选择，相对于喷嘴和气流条件的晶体位置，可以避免可检测的冷凝。然而，有时这在实践中无法实现（来自较小晶体的衍射较差，需要将晶体定位在某些方向以实现所需的数据完整性，需要减少氦气消耗等。）。对于层流气流平行于包含样品的毛细管的粉末实验，以及对于样品相对较小且几乎连续旋转的同步加速器实验，结冰问题似乎不太常见，这有助于被冰覆盖气体流量。最后一种技术原则上也可以应用于使用实验室衍射仪的单晶 X 射线衍射——晶体的周期性快速旋转可以帮助最大限度地减少任何结冰，但是当冷凝速率与一帧数据收集。样品晶体周围的涂层会降低衍射数据的质量，涂层下方样品的温度可能与仪器报告的低温恒温器喷嘴处的温度显着不同。