Wavelength-dependent photodesorption of VUV-inactive molecular ices (N2 Ar, Kr) induced by VUV-excited CO ice

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蕭力捷(Li-Chieh Hsiao) 查詢紙本館藏

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物理學系

論文名稱

(Wavelength-dependent photodesorption of VUV-inactive molecular ices (N2 Ar, Kr) induced by VUV-excited CO ice)

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摘要(中)

光致脫附使冷凝的固態分子變為氣相，是造成分子雲中氣態分子異常豐富的原因之一。在實驗室中通過星際能量作用系統模擬可形成分子冰晶的天文環境，並以國家同步輻射研究中心天光光束線所提供之單色真空紫外線照射。本次實驗主要探討一氧化碳冰晶之光致脫附，結果證實分子冰晶脫附效益與分子受光激發之電子躍遷機率有關。且通過在一氧化碳冰晶上覆蓋不吸收真空紫外線的分子（如氮氣，氬氣或氪氣）生成雙層冰晶並以真空紫外線照射，結果表明受光激發之分子將部分能量給予鄰近分子並使其脫附為使光致脫附主要機制。同時在本研究中提出了一個模型，該模型可以良好的描述本次實驗數據，並可得知真空紫外線導致之脫附受分子冰晶的表面分子的組成、分子間結合能和冰晶之熱擴散係數的影響。

摘要(英)

The photon-stimulated desorption, or the photodesorption, is a pathway to make condensed molecules introduce into gas phase. It is a candidate to solve the abnormal abundance of gaseous molecules in the cold, dense cloud. The astronomical environment to form the molecular ice is simulated by Interstellar Energetic-Process System in laboratory. The irradiation of monochromatic vacuum ultraviolet (VUV) from National Synchrotron Radiation Research Center on CO, carbon monoxide, ice confirms the process of Desorption Induced by Electronic Transition. Through covering VUV-inactive molecules, such as N2, Ar or Kr, on 13CO and irradiate the designed two-layer ices, the results shows that indirect DIET is the main process to make molecules desorb. Meanwhile, a model is proposed in this study that can fit our experimental data, and the results indicate that VUV-photodesorption is affected by surface composition, binding energy and thermal diffusivity of the molecular ices.

關鍵字(中)

★ 一氧化碳
★ 光致脫附
★ 分子冰晶
★ 緻密雲
★ DIET

關鍵字(英)

★ CO
★ photodesorption
★ molecular ice
★ dense cloud
★ DIET

論文目次

Contents
page
摘要 v
Abstract vii
Acknowledgement ix
Contents xi
1 Introduction 1
2 Experimental Set-up, Method 3
2.1 Experimental Set-up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1.1 The Experimental Environment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1.2 Detection Devices. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1.3 The VUV Source from NSRRC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2 Experimental Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2.1 QMS Quantitative Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2.2 Definition of Photodesorption Rate and Yield . . . . . . . . . . . . . . . . . . . . . . . . 6
2.2.3 Quantize Condensed Molecules by FTIR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.2.4 Quantize Condensed Molecules by QMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.3 Experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.3.1 Deposition of the Ices. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.3.2 Monochromatic Light Scanning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.3.3 Temperature Programmed Desorption (TPD) . . . . . . . . . . . . . . . . . . . . . . . . 10
3 Results and discussion 11
3.1 Desorption Yield and VUV Absorbance of the Ices . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.1.1 The Relative Desorption Yield . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
3.1.2 Factors Influencing Relative Desorption Yield . . . . . . . . . . . . . . . . . . . . . . . . 16
3.1.3 Direct and Indirect DIET in Two-Layer Ices . . . . . . . . . . . . . . . . . . . . . . . . . 17
3.2 The Model for the Relative Desorption Yield . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
3.2.1 Relative Desorbing Ability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
xiCONTENTS
3.2.2 Coverage Ratio on the Surface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
3.2.3 Relative Resorption Energy at the Surface . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
3.3 Comparison between fitting parameter and direct measurement . . . . . . . . . . . . 19
4 Conclusions 21
Bibliography 23

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指導教授

陳俞融(Yu-Jung Chen)

審核日期

2020-7-29

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