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研究生:林志民
研究生(外文):Lin, Jim Jr-Min
論文名稱:以交叉分子束方法研究單重態氧原子與小分子之反應動態學
論文名稱(外文):Crossed Molecular Beam Studies of the Reaction Dynamics of O(1D) with Small Molecules
指導教授:李遠哲李遠哲引用關係---
指導教授(外文):Yuan Tseh Lee
學位類別:博士
校院名稱:國立臺灣大學
系所名稱:化學系
學門:自然科學學門
學類:化學學類
論文種類:學術論文
論文出版年:1998
畢業學年度:86
語文別:英文
論文頁數:143
中文關鍵詞:交叉分子束單重態氧原子反應動態學光分解
外文關鍵詞:Crossed BeamO(1D)Reaction DynamicsPhoto dissociation
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新一代的交叉分子束儀器,在本實驗室研製成功,並已完成了數個實驗。相對於其他
類似的儀器,此新儀器有以下的特點:首先,真空系統採用無油的磁浮渦輪分子幫浦,以
降低碳氫化合物之背景;其次,偵測器除了有液氮冷凝阱外,另外加裝循環式氦冷頭冷凝
阱,使真空度能達到1×10-12托耳,氫氣之背景降低了數十倍,使偵測光解反應之氫原子
或氫分子產物容易許多;再其次,除了偵測器可在水平面上轉動外,二個分子束源之其一
,可繞雷射光束在垂直面上轉動,方便產生原子或自由基束源;最後,偵測器之質量過濾
器,改用自行訂製之大尺寸四極柱,其直徑為31.75公釐,與市面上19公釐四極柱比較,
離子穿透率可增為三倍以上。利用此儀器,我們研究了一些小分子,如O2,ClO2,C2H4等
,在無碰撞狀況下的光分解反應。O2在波長157.6奈米單光子激發後,除了主要產生O(1D)
+ O(3P)外,另測得O(3P) + O(3P)之次要途徑,產率只有(0.55±0.05) %,其非等向分佈
係數β= 0. 92±0.02,與主要途徑β= 2.0甚不相同。此結果可幫助了解O2各激發態之間
的交互作用。ClO2在相同激發能量的光分解,有二體分解(ClO + O)及三體分解(Cl + O +
O)兩個途徑。其中,三體分解之大部份的產物能態分佈為Cl(2P) + O(1D) + O(3P),且所
產生的三個原子,是在一個轉動週期內"同時"分開。 C2H4在157.6奈米之光解,有脫氫原
子及脫氫分子二個途徑,利用不同的同位素取代,發現不但三中心及四中心脫氫分子反應
之產率及平移動能分佈甚為不同,且有相當強烈的同位素效應。在交叉分子束的實驗方面
,O(1D)與CH4的反應,測得氫原子及氫分子途徑,主要產物可指認為H2COH + H。O(1D)與
SiH4的反應,亦測得氫原子及氫分子途徑。這兩個反應大部份產物的角分佈,接近等向分
佈,意謂其反應中間體的存活時間,長於轉動週期。
A new crossed molecular beam apparatus has been built to study the
reaction dynamics of molecular photodissociation or bimolecular reactive
scattering. This new apparatus has a number of advantages over similar
apparatus. The vacuum pumps are oil-free magnetic suspended turbo
molecular pumps which help reduce hydrocarbon background. A closed cycle
helium refrigerator has been installed in the detector as cryopumping surface
to achieve 1x10-12 torr. The H2 background count rate is reduced by a factor
of 30*50. The quadrupole rods of the mass filter in the detector has been
modified to a larger quadrupole rods of 31.75 mm diameter which increases
the ion transmission by a factor of three in comparison to the largest
commercial available quadrupole rods (19 mm diameter). In order to generate
atom or radical beam, one of the molecular beam sources can rotate vertically
around the laser beam. In this thesis, photodissociation dynamics of O2,.
ClO2, and C2H4 at 157.6 nm excitation wavelength and reaction dynamics of
O(1D) + CH4, O(1D) + SiH4, O(1D) + Cl2, O(1D) + CHFCl2, and O(1D) + CFCl3 were
studied by crossed molecular beam method. In O2 photodissociation, both
O(1D) + O(3P) and O(3P) + O(3P) channels were observed. The later channel
is very minor with the yield of 0.0055±0.0005, and b = 0.92±0.02 which is
very different from the b = 2.0 for the major channel O(1D) +
O(3P). In ClO2
photodissociation, both two body dissociation, ClO + O, and three body
dissociation, Cl + O + O, were observed. It is most likely the three
fragments dissociate simultaneously within one rotational period. In
photodissociation of 1,2-cis-CD2CH2, 1,2-trans-CD2CH2 and 1,1-CD2CH2, both
three center and four center H2, HD, and D2 molecular elimination channels
were resolved. The relative yields and dynamics of these channels are all
significantly different. In the reaction of O(1D) + CH4 and O(1D) + SiH4,
the H product channels and the H2 product channels were measured. The major
products of the O(1D) + CH4 reaction can be identified as CH2OH
+ H. The H2
elimination channels in O(1D) + SiH4 case is more significant than that in
O(1D) + CH4 case. In both reactions, nearly isotropic angular
distributions for
the H product channels indicate the existence of reaction intermediates.
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