在超高真空環境中以Br2C＝CF2為前驅物，於銅(111)的表面上製備二氟乙烯基中間體(difluorovinylidene, Cu=C=CF2) ，由程溫脫附技術(Temperature Programmed Desorption, TPD)發現在445K生成四碳偶合F3C－C≡C－CF3氣相產物。考量氟原子數的增加，表示Cu=C=CF2極可能在表面經氟化反應轉換成某種C2F3基團。但是反射式吸收紅外光譜(Reflection-Adsorption Infrared Spectroscopy, RAIRS)數據和過往文獻上的CF=CF2以及C−CF3振動頻率存在差異，推論中間體並非單純的CF=CF2和C−CF3。以超共軛(hyperconjugation)概念為基礎，配合密度泛函理論(Density function theory, DFT)計算，得到可解釋紅外光譜差異的兩個過渡態，稱之為準vinyl及準ethylidyne (quasi-vinyl and -ethylidyne)。依照變溫光譜和DFT計算的結果，判定表面中間體的相對穩定程度為vinyl > quasi-ethylidyne > quasi-vinyl > vinylidene > ethylidyne。最後，脫附終產物推測是由quasi-ethylidyne偶合並演變為partial allenic型態而生成。

We investigated the reactivity of difluorovinylidene groups (C2F2) on Cu(111) under ultrahigh vacuum conditions. Difluorovinylidene moieties bonded to surface were generated by the dissociative adsorption of 1,1-dibromodifluoroethylene. Temperature Programmed desorption (TPD) and reflection-adsorption infrared spectroscopy (RAIRS) revealed the thermal reaction pathways, and a variety of intermediates were identified or inferred. The major desorption product, hexafluoro-2-butyne (C4F6), was detected at 445 K. It invokes a step of fluoride addition to difluorovinylidene to render the intermediacy of C2F3. However, differences exist when the vibration data from F + C=CF2 were compared with those from C−CF3 and CF=CF2 in previous literature, implying that the form is neither ethylidyne nor vinyl. Based on the concept of fluorine hyperconjugation, density function theory (DFT) calculations were utilized to obtain two transition states, quasi-vinyl and -ethylidyne, which can account for the differences present in the IR spectra. The relative thermal stability follows the trend of vinyl > quasi-ethylidyne > quasi-vinyl > vinylidene > ethylidyne suggested by IR and DFT calculations. Finally, the end product, CF3C≡CCF3, might be formed by coupling of two quasi-ethylidyne species via the partial allenic forms.

Chapter 1. Introduction...........................................................................1

Chapter 2. Experiments.....................................................3
2.1 Experimental Part........................................................3
2.2 Computational Part.....................................................5

Chapter 3. Results and Interpretations..........................6
3.1 A C−C Coupling Product, Hexafluoro-2-butyne (C4F6), Occurs at 445 K.....................................................7
3.2 The TPD Spectra from Cl3C−CF3 and I−CF=CF2 Give Similar End Products as Those from Br2C=CF2 at Low Coverages.............................................................14
3.3 Temperature-dependent RAIRS of Difluorovinylidene Are Similar to Those from Trifluoroethylidyne at 240 K.............................................18
3.3.1 RAIRS of Surface-bound Difluorovinylidene and CF3C≡CCF3.....................................................................18
3.3.2 RAIRS of Trifluoroethylidyne..................................24
3.4 Temperature-dependent RAIRS of Vinylidene, Ethylidyne and Vinyl Bear Similarities at 300 K...........28
3.5 The concept of Fluorine Hyperconjugation Is a Possible Explanation for the IR Bands around 1500cm-1............................................................................31
3.6 C=CH2(ad) (vinylidene) Isomerizes to Acetylene, while C=CHF(ad) Undergoes F-addition and CC Coupling..............................................................................34
Chapter 4. Discussion....................................................39
4.1 The Form of the Fluorine Addition to Difluorovinylidene Is Neither C−CF3(ad) Nor CF=CF2(ad).......................................................................................39
4.2 The Source of Atom Might Be Due to the Interconversion between Difluorovinylidene and Metal-bound Difluoroacetylene..................................................43

Chapter 5. Conclusions..................................................44

References.........................................................................45

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