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We constructed a simple atomic hydrogen source mounted on a con‰at ‰ange with an outer diameter of 70 mm (CF70). The source consists of a tungstenˆlament, a hydrogen gas inlet, and two feedthroughs. Theˆlament is surrounded by a CF70 nipple made of 0.2z beryllium copper alloy and oxygen-free cupper gaskets to reduce the outgassing rate. Using this hydrogen source, we hydrogenated a clean Si(111)-7×7 surface at room temperature. Low energy electron diŠraction patterns and Auger electron spectra were measured before and after the hydrogenation.

Synopsis In some cases of the ion mobility measurements in cooled He gas, we have observed the separation of electronic states for small molecular ions. Both NH+ and ND+ show the separation of X2Π and a4Σ states. The meta-stable ND 2 + and NH 3 + were observed, but these of NH 2 + and ND 3 + do not appear in the measurements. The reason of the isotope dependence in mobility measurement is discussed using the calculated potential energy curves for NH 2 + and ND 2 + .