Mabbs Richard, Surber Eric, Sanov Andrei
Department of Chemistry, University of Arizona, Tucson, AZ 85721-0041, USA.
J Chem Phys. 2005 Feb 1;122(5):54308. doi: 10.1063/1.1839861.
Photoelectron spectra and angular distributions in 267 nm detachment of the I(-)Ar, I(-)H(2)O, I(-)CH(3)I, and I(-)CH(3)CN cluster anions are examined in comparison with bare I(-) using velocity-map photoelectron imaging. In all cases, features are observed that correlate to two channels producing either I((2)P(3/2)) or I((2)P(1/2)). In the photodetachment of I(-) and I(-)Ar, the branching ratios of the (2)P(1/2) and (2)P(3/2) channels are observed to be approximately 0.4, in both cases falling short of the statistical ratio of 0.5. For I(-)H(2)O and I(-)CH(3)I, the (2)P(1/2) to (2)P(3/2) branching ratios are greater by a factor of 1.6 compared to the bare iodide case. The relative enhancement of the (2)P(1/2) channel is attributed to dipole effects on the final-state continuum wave function in the presence of polar solvents. For I(-)CH(3)CN the (2)P(1/2) to (2)P(3/2) ratio falls again, most likely due to the proximity of the detachment threshold in the excited spin-orbit channel. The photoelectron angular distributions in the photodetachment of I(-), I(-)Ar, I(-)H(2)O, and I(-)CH(3)CN are understood within the framework of direct detachment from I(-). Hence, the corresponding anisotropy parameters are modeled using variants of the Cooper-Zare central-potential model for atomic-anion photodetachment. In contrast, I(-)CH(3)I yields nearly isotropic photoelectron angular distributions in both detachment channels. The implications of this anomalous behavior are discussed with reference to alternative mechanisms, affording the solvent molecule an active role in the electron ejection process.
利用速度映射光电子成像技术，研究了I(-)Ar、I(-)H₂O、I(-)CH₃I和I(-)CH₃CN团簇阴离子在267nm光解离时的光电子能谱和角分布，并与裸I(-)进行了比较。在所有情况下，均观察到与产生I((2)P(3/2))或I((2)P(1/2))的两个通道相关的特征。在I(-)和I(-)Ar的光解离中，(2)P(1/2)和(2)P(3/2)通道的分支比约为0.4，两种情况下均低于统计比值0.5。对于I(-)H₂O和I(-)CH₃I，(2)P(1/2)与(2)P(3/2)的分支比相比裸碘化物情况大1.6倍。(2)P(1/2)通道的相对增强归因于在极性溶剂存在下对末态连续波函数的偶极效应。对于I(-)CH₃CN，(2)P(1/2)与(2)P(3/2)的比值再次下降，最可能是由于激发自旋轨道通道中解离阈值的接近。I(-)、I(-)Ar、I(-)H₂O和I(-)CH₃CN光解离中的光电子角分布可在从I(-)直接解离的框架内得到理解。因此，使用用于原子阴离子光解离的Cooper-Zare中心势模型的变体对相应的各向异性参数进行建模。相比之下，I(-)CH₃I在两个解离通道中产生几乎各向同性的光电子角分布。参照替代机制讨论了这种异常行为的影响，赋予溶剂分子在电子喷射过程中一个积极作用。
