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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Local Ionization in 2-Phenylethyl-N,N-dimethylamine: Charge Transfer and Dissociation Directly after Ionization
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Local Ionization in 2-Phenylethyl-N,N-dimethylamine: Charge Transfer and Dissociation Directly after Ionization

机译：2-苯基乙基-N，N-二甲基胺中的局部电离：电离后直接进行电荷转移和离解

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The 2-phenylethyl-N,N-dimethylamine (PENNA) radical cation offers two functional groups for a positive charge to reside, the benzyl ring and the substituted amine group. Previously published HeI photoelectron spectra (PES) and our B3LYP data of the cation ground state agree that the amine site has the lowest ionization energy (IE). In this work we present evidence that by resonant laser multiphoton ionization the electron is removed from the phenyl site. B3LYP calculations of the neutral molecule predict that by far the most stable structure is the nonsymmetric unfolded anti conformer and that no other conformer should be significantly populated. This is confirmed by the S_0-S_1 resonant two-photon ionization (R2PI) spectrum in which one conformer is found to be predominant. The presence of the vibrational fingerprint of the phenyl chromophore and the absolute energetic position of the R2PI spectrum clearly show the local character of the first photoexcitation. Surprisingly, the R2PI mass spectra taken via S_1 resonances show strong fragmentation. The parent-to-fragment-ion ratio is about 1:10 and mostly independent to laser intensity. The metastable character of the decay excludes a fragmentation caused by cation photoabsorption. The strong dissociation directly after ionization is explained by (i) a local ionization at the phenyl chromophore, (ii) a fast charge transfer (CT) to the lower-energetic amine site, and (iii) a subsequent metastable dissociation. A first detailed analysis of the ionization process indicates that intersite R2PI ionization between local states is a one-photon two-electron process which is expected to be improbable and that a failure of local ionization only happens in cases of mixed intermediate S_1 states or mixed cation states. PENNA with two possible charge sites spaced by a -CH_2-CH_2- bridge is an ideal model system to study the dynamics of a downhill charge transfer after local ionization to the first excited cation state as presented in a forthcoming paper.
机译：2-苯基乙基-N，N-二甲基胺（PENNA）自由基阳离子提供两个用于带正电荷的官能团，即苄环和取代的胺基。先前发布的HeI光电子能谱（PES）和我们的阳离子基态的B3LYP数据都认为胺位具有最低的电离能（IE）。在这项工作中，我们提供证据表明，通过共振激光多光子电离，电子从苯基位置被去除。中性分子的B3LYP计算预测，到目前为止，最稳定的结构是非对称的未折叠抗构象异构体，并且不应显着填充其他构象异构体。这由S_0-S_1共振双光子电离（R2PI）光谱证实，在该光谱中发现一个构象体占主导地位。苯基发色团的振动指纹和R2PI光谱的绝对能量位置的存在清楚地表明了第一次光激发的局部特征。出人意料的是，通过S_1共振获得的R2PI质谱图显示出很强的碎片。母体与碎片离子之比约为1:10，并且大部分与激光强度无关。衰减的亚稳态特征排除了阳离子光吸收引起的碎裂。直接电离后的强离解可以通过（i）苯基发色团上的局部电离，（ii）快速电荷转移（CT）到低能胺位点以及（iii）随后的亚稳解离来解释。对电离过程的首次详细分析表明，局部状态之间的位点间R2PI电离是单光子双电子过程，预计这是不可能的，并且局部电离失败仅在混合的中间S_1状态或混合阳离子的情况下发生状态。 PENNA具有两个可能的电荷位点，它们之间由-CH_2-CH_2-桥隔开，是一种理想的模型系统，如即将发表的论文中所述，它是研究局部电离到第一个激发阳离子状态后下坡电荷转移动力学的方法。

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