An experimental and theoretical investigation of the competition between chemical reaction and relaxation for the reactions of 1CH2 with acetylene and ethene: implications for the chemistry of the giant planets
An experimental and theoretical investigation of the competition between chemical reaction and relaxation for the reactions of 1CH2 with acetylene and ethene: implications for the chemistry of the giant planets
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DOI：
10.1039/c004131a
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发表时间：
2010-01-01
影响因子：
3.4
通讯作者：
Harvey, Jeremy N.
中科院分区：
文献类型：
--
作者：
Gannon, Kelly L.;Blitz, Mark A.;Harvey, Jeremy N.
用激光诱导荧光法测定了亚甲基第一激发态（a（1）A（1）（CH_2）-C ~（-1））与乙炔和乙烯反应生成H原子的分支比随温度的变化关系，反应温度为195，250和298 K，总压近似为1 Torr，将所述信号与从校准反应观察到的信号进行比较。与乙炔反应时，H的产率从0.28（195 K）增加到0.53（250 K），再增加到0.88（298 K）。（CH_2）-C-1与乙烯反应的H原子产率表现出类似的行为，产率分别为0.35（195 K），0.51（250 K）和0.71（298 K）。副产物炔丙基（C3 H3）和烯丙基（C3 H5）分别由化学活化的C3 H4和C3 H6中间体解离而成，是在外行星和土卫六大气中形成高级烃（包括苯）的重要物质。H原子的产生与电子弛豫竞争以形成基态亚甲基（（XB 1）-B-3，（CH 2）-C-3）和与碰撞稳定化竞争以形成C3 H4和C3 H6。主方程的计算表明，在实验条件下，（CH_2）-C_1与乙炔的反应中碰撞稳定化不明显，反应平衡是由于电子弛豫引起的。用非绝热过渡态理论研究了（CH_2）-C_1与乙炔的反应。计算结果与实验结果基本吻合，一般在误差范围内，并再现了电子弛豫的负温度依赖性。本文讨论了（CH_2）-C ~（-1）与惰性气体、氢气、乙炔和乙烯反应的绝对速率系数与温度的关系以及化学反应与电子弛豫的分支比的关系。
The temperature dependence of the branching ratios for H atom production from the reactions of the first excited state of methylene (a(1)A(1) (CH2)-C-1) with acetylene and ethene have been measured at similar to 1 Torr total pressure and temperatures of 195, 250 and 298 K by monitoring the production of H atoms using laser induced fluorescence, comparing the signal to that observed from a calibration reaction. For the reaction with acetylene the yield of H increases from 0.28 (195 K) to 0.53 (250 K) to 0.88 at 298 K. The H atom yield from the reaction of (CH2)-C-1 with ethene shows similar behaviour, the yields being 0.35 (195 K), 0.51 (250 K) and 0.71 (298 K). The co-products, propargyl (C3H3) and allyl (C3H5) are formed from the dissociation of chemically activated C3H4 and C3H6 intermediates respectively, and are important species in the formation of higher hydrocarbons, including benzene, in the atmospheres of the outer planets and Titan. H atom production is in competition with electronic relaxation to form ground state methylene ((XB1)-B-3, (CH2)-C-3) and collisional stabilization to form C3H4 and C3H6. Master equation calculations have been carried out to demonstrate that for the reaction of (CH2)-C-1 with acetylene, collisional stabilization is insignificant under experimental conditions and hence the balance of reaction is due to electronic relaxation. Non-adiabatic transition state theory has been applied to the reaction of (CH2)-C-1 with acetylene. The calculations show reasonable agreement with experiment, generally being within the combined errors, and reproduce the negative temperature dependence for electronic relaxation. The implications of the temperature dependence of the absolute rate coefficients for (CH2)-C-1 reactions with inert gases, hydrogen, acetylene and ethene and of the branching ratios between chemical reaction and electronic relaxation are discussed.