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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >UV-Absorption Spectra of the Radical Transients Generated from the 193-nm Photolysis of Allene,Propyne,and 2-Butyne
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UV-Absorption Spectra of the Radical Transients Generated from the 193-nm Photolysis of Allene,Propyne,and 2-Butyne

机译：丙二烯，丙炔和2-丁炔在193 nm光解中产生的自由基瞬态的紫外吸收光谱

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摘要

The 193-nm photochemistry of allene (H_2C=C=CH_2),propyne (H_3C-Cident toCH),and 2-butyne (H_3C-Cident toC-CH_3) has been examined,and the UV spectral region between 220 and 350 nm has been surveyed for UV-absorption detection of transient species generated from the photolysis of these molecules.Time-resolved UV-absorption spectroscopy was used for detection of transient absorption.Gas chromatographic/mass spectroscopic (GC/MS) analysis of the photolyzed samples were employed for identification of the final photodissociation products.An emphasis of the study has been on the examination of possibilities of formation of different C_3H_3 isomeric radicals,that is,propargyl (H_2CCCH) or propynyl (H_3CCC),from the 193-nm photolysis of these molecules.Survey of the UV spectral region,following the 193-nm photolysis of dilute mixtures of allene/He resulted in detection of a strong absorption band around 230 nm and a weaker band in the 320-nm region with a relative intensity of about 8:1.The time-resolved absorption traces after the photolysis event show an instantaneous rise,followed by a simple decay.The spectral features,observed in this work,following 193-nm photolysis of allene are in good agreement with the previously reported spectrum of H_2-CCCH radical in the 240- and 320-nm regions and are believed to originate primarily from propargyl radicals.In comparison,the spectra obtained from the 193-nm photolysis of dilute mixtures of HCCCH_3/He and CH_3-CCCH_3/He were nearly identical,consisting of two relatively broad bands centered at about 240- and 320-nm regions with a relative intensity of about 2:1,respectively.In addition,the time-resolved absorption traces after photolysis of propyne and 2-butyne samples,both in the 240 and 320 nm regions,indicated an instant rise followed by an additional slower absorption rise.The distinct differences between the results of allene with those of propyne and 2-butyne suggest the observed absorption features following 193-nm photolysis of these molecules are likely to be composite with contributions from a number of transient species other than propargyl radicals.Propyne and 2-butyne are structurally similar.The methyl (CH_3) and propynyl (CH_3Cident toC) radicals are likely to be among the photodissociation products of 2-butyne,and similarly,propynyl is likely to be a photodissociation product of propyne.GC/MS product analysis of photolyzed 2-butyne/He mixtures indicates the formation of C_2H_6 (formed from the combination of CH_3 radicals),and a number of C_6H_6 and C_4H_6 isomers formed from self- and cross reactions of C_3H_3 and CH_3 radicals,including 1,5-hexadiyne and 2,4-hexadyine,that are potential products of combination reactions of propargyl as well as propynyl radicals.
机译：研究了193nm的丙二烯（H_2C = C = CH_2），丙炔（H_3C-Cident toCH-3）的光化学，并且在220至350 nm之间的紫外光谱区具有对这些分子的光解产生的瞬态物质进行了紫外吸收检测，使用了时间分辨紫外吸收光谱检测了瞬态吸收，并采用了气相色谱/质谱（GC / MS）分析光解样品用于鉴定最终的光解离产物。研究的重点是从这些分子的193 nm光解中检查形成不同的C_3H_3异构基团，即炔丙基（H_2CCCH）或炔丙基（H_3CCC）的可能性。在对193.nm的丙二烯/ He稀混合物进行光解之后，对UV光谱区域进行了调查，结果发现在230 nm附近有一个强吸收带，在320 nm附近则有一个较弱的带，相对强度约为8： 1.t在光解事件之后的ime分辨的吸收迹线显示出瞬时上升，随后是简单的衰减。在这项工作中观察到，在193 nm的丙二烯光解之后的光谱特征与先前报道的H_2-CCCH自由基光谱高度吻合相比之下，从HCCCH_3 / He和CH_3-CCCH_3 / He的稀混合物的193nm光解获得的光谱几乎相同，由以下组成：炔丙基。两个相对较宽的谱带分别位于约240和320 nm区域，相对强度分别约为2：1。此外，在丙炔和2-丁炔样品的光解后，时间分辨吸收迹线分别在240和240 nm中。 320 nm区域，表明立即上升，随后吸收吸收又出现了缓慢的下降。丙二烯与丙炔和2-丁炔的结果之间的明显差异表明，在193 nm照片下观察到的吸收特征这些分子的裂解很可能是由炔丙基自由基以外的许多瞬态物种贡献的复合物。丙炔和2-丁炔在结构上相似。甲基（CH_3）和丙炔基（CH_3Cident toC）自由基可能在光解离中2-丁炔的产物，类似地，丙炔可能是丙炔的光解产物。光解2-丁炔/ He混合物的GC / MS产物分析表明，形成了C_2H_6（由CH_3自由基的组合形成），并且由C_3H_3和CH_3自由基的自和交叉反应形成的C_6H_6和C_4H_6异构体的数量，包括1,5-己二炔和2,4-己基，它们是炔丙基和丙炔基结合反应的潜在产物。

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