近年來，有不少研究致力於絕熱膨脹效應對水氣吸附現象的探討，但由於受限於分析儀器之限制，大部份之方法皆無法從一大氣壓時便開始分析訊號。然而，此段時間可能是造成表面水氣附著的重要階段，因此本實驗的主要目的是建立一套新的實驗方法以有效的將分析條件逼近一大氣壓，以觀察表面水氣吸附現象。
本實驗的重點是設計並建立一套紅外光分析系統以探討真空腔中的水氣吸附現象，本實驗另包含：（一）利用傅立葉分光術擷取紅外光的光譜訊號（二）氣體淨化系統對移除系統內的水氣與二氧化碳的研究及（三）建立電場偏振調制方法以抑制光路上的氣體吸收干擾。實驗系統光路經測試、微調後可取得理想的紅外光之干涉訊號。而氣體淨化系統在改善系統的密合度之後，可抑制外部的氣體滲入並有效的移除系統內的水氣與二氧化碳，且於此氣體流動下，麥克森干涉光路之移動鏡仍可維持其穩定性。在水氣混合N2及He氣體之測試實驗中，發現於抽氣時，因絕熱膨脹效應導致最低溫度分別下降至-47.6 oC（N2）與-68.1 oC（He）。而於抽氣後4.7秒內，混合氮氣時之水氣吸收率比混合氦氣之情況下還高約0.005 arbitrary units∼0.01 arbitrary units。另外，在偏振調制測試實驗中發現，當雙通道干涉譜之振幅比值小於1.26時，可濾除光路上的氣體吸收干擾，顯示本實驗建立之紅外光系統及電場偏振調制方法可觀察到樣品表面之吸附訊號，而增進對真空腔中水氣之吸附了解。
目前僅將偏振調制方法應用於量測標準樣品片(poly-l-lysine film on a gold-coated substrate)，未來仍需量測真空材料表面的吸收光譜，並將光譜訊號轉換為表面覆蓋度單位，以探討絕熱膨脹效應造成水氣吸附的現象。

Adiabatic expansion has the effect of causing adsorption of water on surfaces, but present analytical instruments do not allow implementation of an analysis beginning with pumping from atmospheric pressure, which is an important range in relation to the adsorption of water vapor on a sample surface. The purpose of this work is to establish a new experimental method to investigate the phenomenon of adsorption of water on a surface at pressures near atmosphere.
The main emphases of this work are the design and construction of a system for infrared analysis to investigate the phenomenon of adsorption of water inside a vacuum chamber. The experiment involves (a) a Fourier spectroscopic analysis to obtain spectral signals about the incident infrared, (b) a purge mechanism for a purified gas to remove water vapor and carbon dioxide from the system, and (c) an application of an electric field with polarized modulation to suppress interference from signals of gases absorbing in the light path. After testing and fine-tuning the light path, the experimental system can obtain the interference signals of infrared radiation. The sealing of the gas purge system has been improved to effectively eliminate the permeation of gases such as water vapor and carbon dioxide from the outside. The movable mirror in the Michelson interferometer maintains its stability independent of the rate of flow of the purge gas. During test experiments on filling the chamber with nitrogen or helium mixed with water vapor, the measured temperatures decreased to -47.6 oC（N2) and -68.1 oC（He) during evacuation reflecting the effect of adiabatic expansion. The absorption signal of water vapor after pumping for 4.7 s is about 0.005∼0.01 arbitrary units higher for the N2 / H2O gaseous mixture than for the He / H2O gaseous mixture. Tests of the polarization modulation technique indicate that signals from absorbing gases in the light path are removed when the ratio of the summation signal (amplitude of channel B) to the differential signal (amplitude of channel A) is less than 1.26. The result demonstrates the capability of observing a signal due to molecules adsorbed on a surface with an infrared analysis system and a polarization modulation technique, so as to improve our understanding of adsorption of water in a vacuum chamber.
For purposes of testing, we applied the polarization modulation technique only on a standard sample (poly-l-lysine film on a gold-coated substrate). To investigate the effect of adiabatic expansion leading to the phenomenon of water adsorption, future work will focus on measuring adsorption spectra for materials in vacuum chambers and transforming spectral signals to units of surface coverage.

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