Xu Hong, Pratt S T
Argonne National Laboratory, Argonne, Illinois 60439, United States.
J Phys Chem A. 2015 Jul 16;119(28):7548-58. doi: 10.1021/acs.jpca.5b00860. Epub 2015 Jun 1.
We have determined the I (2)P3/2 and (2)P1/2 branching fractions following the photodissociation of methyl iodide (CH3I) via a number of vibronic bands associated with the B̃ ((2)E3/2)6s Rydberg state at excitation wavelengths between 201.2 and 192.7 nm. Vacuum ultraviolet light at 118.2 nm was used to ionize both the product iodine atoms and the methyl radical cofragments, and velocity map ion imaging was used to determine the product translational energy distributions and angular distributions. The known relative photoionization cross sections for I (2)P3/2 and (2)P1/2 at 118.2 nm were used to determine the corresponding branching fractions. The results extend our earlier work at 193 nm by Xu et al. (J. Chem. Phys. 2013, 139, 214310), and complement the closely related work of González et al. (J. Chem. Phys. 2011, 135, 021102). We find that for most of the excited vibronic levels of the B̃ state studied, the I (2)P3/2 branching ratio is small, but nonzero, and that this channel is associated with internally excited CH3 radicals. The results are discussed in relation to the recent theoretical results of Alekseyev et al. (J. Chem. Phys. 2011, 134, 044303).
我们通过与B̃((2)E3/2)6s里德堡态相关的多个振转带，在201.2至192.7纳米的激发波长下，测定了碘化甲烷（CH3I）光解离后的I(2)P3/2和(2)P1/2分支比。利用118.2纳米的真空紫外光使产物碘原子和甲基自由基共碎片离子化，并采用速度成像技术来确定产物的平动能分布和角分布。利用已知的I(2)P3/2和(2)P1/2在118.2纳米处的相对光电离截面来确定相应的分支比。这些结果扩展了Xu等人（《化学物理杂志》，2013年，139卷，214310页）在193纳米处的早期工作，并补充了González等人（《化学物理杂志》，2011年，135卷，021102页）的密切相关工作。我们发现，对于所研究的B̃态的大多数激发振转能级，I(2)P3/2分支比很小但不为零，且该通道与内部激发的CH3自由基相关。结合Alekseyev等人（《化学物理杂志》，2011年，134卷，044303页）最近的理论结果对这些结果进行了讨论。
