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    Title: Ab-initio molecular dynamic simulation studies: 1. temperature induced carbon-halogen dissociated reaction and cα-cα self-coupling reactions 2. stm-tip induced co(ads) desorption reaction and their inelastic electron tunneling spectroscopy
    Other Titles: 第一原理分子動態模擬之理論研究 : 1. 溫度誘導之碳鹵鍵解離及碳碳鍵偶合反應 2. STM針尖誘導CO脫附反應及非彈性電子穿隧光譜
    Authors: 呂紹宇;Lu, Shao-Yu
    Contributors: 淡江大學化學學系博士班
    林志興;Lin, Jyh-Shing
    Keywords: 分子動態模擬;非彈性電子穿隧光譜;反射式紅外光譜模擬;時頻解析;Ab-initio molecular dynamics;Density Functional Theory;time-frequency analysis;inelastic electron tunneling spectroscopy
    Date: 2015
    Issue Date: 2016-01-22 14:52:13 (UTC+8)
    Abstract: 本篇論文透過第一原理分子動態模擬(DFT-based molecular dynamic simulation)來探討(1) 碳氫、碳鹵化合物透過金屬表面催化的碳鹵鍵解離及碳碳鍵偶合反應機制研究。並結合本實驗室所開發的表面反射式紅外光振動光譜(Reflected infrared adsorption spectroscopy)與時頻解析(time-frequency analysis)等光譜模擬工具來觀察分子在反應過程中的光譜變化。(2) 此外我們也透過局域態密度(Local density of state)來產生非彈性電子穿隧光譜(Inelastic electron tunneling spectroscopy),研究STM-tip穿隧電子所誘導的CO脫附反應。

      在論文第一部分,我們成功透過分子動態模擬進行 propargyl bromide (HC≡C(β)-C(α)H2Br(ads))與 propynyl iodide (CH3-C(β)≡C(α)-I(ads))在Ag(111)表面上的碳鹵鍵解離吸附反應,並觀察到銀表面與吸附分子在過渡態時可生成碳銀的鍵結,提升銀表面原子與吸附分子之間的電子非局域化性來誘發碳鹵鍵的解離。催化反應前後的光譜可透過短時間時頻解析(short-time Fourier transform analysis : STFT)的方式直接獲得催化反應前後的光譜訊號,並得到與實驗一致的結果。接著,我們更進一步探討不同混成軌域之吸附分子(methyl acetylide (CH3-C(β)≡C(α)(ads)) and ethyl (H3C(β)-C(α)H2(ads)))在銀表面溫度增溫過程中的擴散能力,追蹤不同溫度下的反應動態。結果顯示,Cα為sp混成的methyl acetylide由於其與表面的鍵結較強(π-back donation效應),因此相較於sp3混成的ethyl需要較高的表面溫度方可進行擴散(500K and 200K)導致較高的碳碳鍵偶合反應溫度。

      在論文第二部分,我們藉由加入STM (Ag5 cluster tip)進行CO在銀表面上STM針尖誘導的分子動態研究。藉由分子動態模擬我們觀察到STM會誘導表面上CO分子進行分子旋轉運動並且形成CO-terminated Ag5 cluster tip。同時,我們搜集動態過程中的局域態密度(local density of state)變化來產生非彈性電子穿隧光譜 (Inelastic electron tunneling spectroscopy) ,並且搭配時頻解析工具成功觀察到CO分子在STM針尖誘導下frustrated rotation與CO stretching之間的非簡諧偶合效應(anharmonic coupling)。最後,我們進一步使用CO-terminated Ag5 cluster tip來模擬CoPz (Cobalt porphyrazin)分子在Ag(110)表面上的非彈性電子穿隧光譜,並成功觀察到與實驗相符合的CO frustrated translation位移訊號。
    Density functional theory (DFT)-based molecular dynamic simulation in combination with time-resolved simulated reflected infrared adsorption spectroscopy is performed to study 1) the dynamic behavior of catalytic reaction for carbon-halogen dissociation and carbon-carbon self-coupling reaction on metal surface. 2) In addition, we performed our new methodology to generate the inelastic electron tunneling spectroscopy by collecting the dynamic trajectories of local density of state (LDOS) to investigate the STM-tip induced CO desorption reaction.

    In the part I of my thesis, firstly, we successfully investigate the adsorption behaviours of carbon-halogen rupture reaction for propargyl bromide (HC≡C(β)-C(α)H2Br(ads)) and propynyl iodide (CH3-C(β)≡C(α)-I(ads)) on Ag(111) surface by using DFT-based MD simulation. We found that the carbon-Ag interaction can induce the weakening of carbon-halogen bond due to the delocalization effect between the adsorbed molecule and Ag surface at transition state. In addition, the time-resolved spectra constructed by short-time Fourier transform (STFT) illustrate that the evolution of all the vibrational modes along the carbon-halogen dissociation reaction and have a good agreement with experimental RAIRS results. Secondly, we investigated the thermally induced diffusion processes of different hybridization state of Cα that is, methyl acetylide (CH3-C(β)≡C(α)(ads) : sp hybridization of Cα atom) and ethyl (H3C(β)-C(α)H2(ads) : sp3 hybridization of Cα atom), respectively. Our results indicate that the CH3-C(β)≡C(α)(ads) is very stable due to the strong π-back donation effect as methyl acetylide adsorbed on Ag(111) surface. Therefore the methyl acetylide will have higher diffusion temperature than that of ethyl on the same surface leading to the higher reaction temperature for the Cα-Cα self-coupling reaction.

    In the part II of my thesis, the DFT-based MD simulation with a Fourier transform of the derivative of local density of states autocorrelation function is introduced to generate the inelastic electron tunnelling spectra for evaluating he effect of STM-tip on adsorption dynamics for CO(ads) on the Ag(110) surface. Based on dynamic results, the STM-tip can induce the desorption process of CO on Ag(110) to produce a functionalized STM-tip (CO-terminated Ag5 cluster tip). By using the STFT, the anharmonic coupling between the frustrated rotation and CO stretching mode can be investigated. Finally, the CO-terminated Ag5 cluster tip can be further used to scan the CoPz (Cobalt porphyrazin) on Ag(110) to generate the local IETS spectrum. Our new methodology successfully observe the frustrated translation of CO vibration senses the spatially varying potential energy landscape of the molecule and its surroundings and have a good agreement with experimental IETS results.
    Appears in Collections:[化學學系暨研究所] 學位論文

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