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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Determination of the Absolute Photoionization Cross Sections of CH3 and I Produced from a Pyrolysis Source, by Combined Synchrotron and Vacuum Ultraviolet Laser Studies
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Determination of the Absolute Photoionization Cross Sections of CH3 and I Produced from a Pyrolysis Source, by Combined Synchrotron and Vacuum Ultraviolet Laser Studies

机译：同步加速器和真空紫外激光研究确定热解源产生的CH3和I的绝对光电离截面

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A pyrolysis source coupled to a supersonic expansion has been used to produce the CH3 radical from two precursors, iodomethane CH3I and nitromethane CH3NO2. The relative ionization yield of CH3 has been recorded at the SOLEIL Synchrotron Radiation source in the range 9.0-11.6 eV, and its ionization threshold has been modeled by taking into account the vibrational and rotational temperature of the radical in the molecular beam. The relative photoionization yield has been normalized to an absolute cross section scale at a fixed wavelength (118.2 nm, σi CH3 ) 6.7-1.8 +2.4 Mb, 95% confidence interval) in an independent laboratory experiment using the same pyrolysis source, a vacuum ultraviolet (VUV) laser, and a carefully calibrated detection chain. The resulting absolute cross section curve is in good agreement with the recently published measurements by Taatjes et al.,1 although with an improved signal-to-noise ratio. The absolute photoionization cross section of CH3I at 118.2 nm has also been measured to be σi CH3I ) (48.2 ( 7.9) Mb, in good agreement with previous electron impact measurements. Finally, the photoionization yield of the iodine atom in its ground state 2P3/2 has been recorded using the synchrotron source and calibrated for the first time on an absolute cross section scale from our fixed 118.2 nm laser measurement, i I2P3/2 ) 74-23 +33 Mb (95% confidence interval). The ionization curve of atomic iodine is in good agreement, although with slight variations, with the earlier relative ionization yield measured by Berkowitz et al.2 and is also compared to an earlier calculation of the iodine cross section by Robicheaux and Greene.3 It is demonstrated that, in the range of pyrolysis temperature used in this work, all the ionization cross sections are temperature-independent. Systematic care has been taken to include all uncertainty sources contributing to the final confidence intervals for the reported results.
机译：与超音速膨胀耦合的热解源已用于由两种前体碘甲烷CH3I和硝基甲烷CH3NO2产生CH3自由基。在SOLEIL同步辐射源处记录的CH3的相对电离产率在9.0-11.6 eV范围内，并且通过考虑分子束中自由基的振动和旋转温度对CH3的电离阈值进行了建模。在独立的实验室实验中，使用相同的热解源，真空紫外光，在相对固定波长（118.2 nm，σiCH3）6.7-1.8 +2.4 Mb，95％置信区间）上，将相对光电离产率标准化为绝对截面比例。 （VUV）激光和精心校准的检测链。所得的绝对截面曲线与Taatjes等人[1]最近发表的测量结果非常吻合，尽管信噪比有所改善。 CH3I在118.2 nm处的绝对光电离截面也被测量为σiCH3I）（48.2（7.9）Mb，与先前的电子撞击测量结果非常吻合，最后，碘原子在其基态2P3 /下的光电离产率2是使用同步加速器源记录的，并通过我们固定的118.2 nm激光测量值i I2P3 / 2）74-23 +33 Mb（95％置信区间）在绝对截面尺度上进行了首次校准。原子碘的电离曲线虽然变化很小，但与Berkowitz等人[2]测得的相对电离得率较早，并与Robicheaux和Greene [3]较早计算出的碘截面进行了比较。证明了在这项工作中使用的热解温度范围内，所有电离截面均与温度无关。已经采取系统的谨慎措施，将所有不确定性源纳入报告结果的最终置信区间。

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