氯氣－臭氧凡得瓦團簇之紫外吸收截面積

Absorption Cross Section of Ozone Chlorine Complex in the UV Region

潘世傑(Shih-Chieh Pan)

指導教授 ： 洪偉修 ； 林志民

國立臺灣師範大學/理學院/化學系/碩士(2012年)

摘要

凡得瓦團簇的紅外光譜已經有相當多的研究，但是凡得瓦團簇在紫外光譜的研究卻相當的少見。使用分子束的方法可以產生凡得瓦團簇，但是要產生特定大小的凡得瓦團簇不是一件容易的事。本實驗利用分子束，產生了氯氣－臭氧之凡得瓦團簇，並且在248 nm、308 nm以及352 nm波長下，測量其吸收截面積。我們偵測吸收截面積的方法，有別於一般的吸收光譜法，是利用分子束與雷射交互作用後，偵測光分解後剩餘的分子數。此方法可以在不知道團簇與單體的濃度下，得知團簇與單體的吸收截面積比例。我們藉由調整分子束的膨脹條件來調整分子束中團簇大小的分布。由於248 nm非常接近臭氧的最大吸收峰，而氯氣在此波長沒有吸收；另一方面，在352 nm，氯氣的吸收遠大於臭氧。於是我們在248 nm及352 nm波長下，觀察了凡得瓦團簇與單體的吸收截面積比值。隨著團簇濃度的增加，團簇吸收截面積比從低濃度開始維持一個定值，到團簇濃度更大時則逐漸地上升。由於凡得瓦團簇形成的機制是由最小的尺寸開始，接著更大的團簇才會形成，所以我們可以知道在團簇濃度低的範圍內，團簇的組成是含一個氯氣以及一個臭氧。最後在308 nm，此波長氯氣以及臭氧皆有吸收。在團簇是氯氣及臭氧以1：1的組成狀態下，團簇的吸收截面積約為氯氣單體吸收截面積的2.070.12倍，約為臭氧單體吸收截面積的3.50.39倍，將團簇的吸收截面積除以兩個單體相加的吸收截面積的比值為1.30.16。而在248 nm以及352 nm的O3Cl2團簇與單體吸收截面積比值分別是0.970.05以及0.770.04。實驗結果顯示，由一個氯氣以及一個臭氧組成的凡得瓦團簇中，凡得瓦力的影響確實會造成吸收光譜帶的變化。

關鍵字

凡得瓦團簇 ； 吸收截面積 ； 分子束

並列摘要

There have been numerous studies on the infrared spectra of weakly bound van
der Waals (vdW) complexes. However, studies of vdW complexes in the UV-Vis
region are relatively rare. Although it is common to synthesize vdW complexes in a
molecular beam, to synthesize a size-specific complex is not trivial. Our previous
work of ozone dimer shows that the absorption cross sections of the complexes are
related to the complex sizes. In this work, we generated a molecular beam which
contained ozone-chlorine vdW complexes, and measured the absorption cross section
ratios of the ozone-chlorine 1:1 vdW complex to its monomers at 248 nm, 308 nm and
352 nm. We employed a new method for determining absorption cross section. The
unique feature of this method is that we do not need the knowledge of absolute
concentration. At 248 nm, absorption of ozone is very strong where chlorine shows no
absorption. At 352 nm, absorption of chlorine is much stronger than ozone. Our data
show that the absorption cross sections of the complex at 248 nm and 352 nm remain
constant at low complex concentrations, indicating that we successfully synthesized
the complex which composes of only one ozone and one chlorine. At 308 nm, both
ozone and chlorine have considerable absorption cross sections. The result shows that
the absorption cross section ratios of the complex to chlorine and ozone monomers
are 2.070.12 and 3.550.39, respectively. And it also implies that the cross section
ratio of the complex over the sum of the monomer’s cross sections is 1.30.16. At 248
nm and 352 nm, cross section ratios of the complex to the monomer sum are
0.970.05 and 0.770.04, respectively. We may conclude that for the ozone-chlorine
complex, the van der Waals interaction perturbs the absorption spectra of monomers.

並列關鍵字

van der waals complex ； absorption cross section ； molecular beam

參考文獻

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