Electronic decoherence induced by intramolecular vibrational motions in a betaine dye molecule
Electronic decoherence induced by intramolecular vibrational motions in a betaine dye molecule
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DOI：
10.1021/jp037031b
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发表时间：
2004-05-27
影响因子：
3.3
通讯作者：
Rossky, PJ
中科院分区：
文献类型：
--
作者：
Hwang, H;Rossky, PJ
研究了甜菜碱分子（4-（1-吡啶基）苯酚盐）中仅由分子内振动引起的电子退相干。分析是基于核重叠/相函数（NOPF），出现在电子约化密度矩阵。要做到这一点，在基态和第一激发态的几何优化和振动的正常模式分析。根据替代近似的相干耗散时间得到，包括分析频移和杜辛斯基旋转的作用。几何优化揭示了地面和第一激发态的中心扭转角之间的巨大差异，与倾斜的几何结构的吡啶环也观察到在第一激发态。然而，杜辛斯基旋转矩阵似乎几乎是对角的，只有少数相当多的非对角元素。我们发现，低频扭转运动不作出任何显着的贡献的衰减的NOPF。频移对NOPF衰变的影响比杜辛斯基旋转更大，但最简单的自旋玻色子模型本身就能很好地描述相干衰变。在与主要高斯衰减相比的时间长的时候，我们也观察到由相位递归调制的指数衰减，但是指数衰减仅在松弛的最后10 - 20%中占主导地位。计算出的相干耗散时间所产生的分子内振动运动的3.7 A是远远短于估计的贡献，由于典型的溶剂分子的退相干时间，表明在溶质分子的核运动可以有更多的影响，总的电子退相干比溶剂分子，即使是一个电荷转移系统，如本案例。
Electronic decoherence induced only by intramolecular vibrational motions is investigated in a betaine molecule, pyridinium N-phenoxide betaine [4-(1-pyridinio)phenolate], having 60 vibrational modes. The analysis is based on the nuclear overlap/phase function (NOPF) that appears in the electronic reduced density matrix. To do so, geometry optimizations and vibrational normal-mode analysis in the ground state and the first excited state are performed. Coherence dissipation times according to alternative approximations are obtained, including analysis of the role of frequency shifts and Duschinsky rotation. Geometry optimization reveals a large difference between the central torsional angles of the ground and the first excited state, with a tilted geometry of the pyridinium ring also observed in the first excited state. Nevertheless, the Duschinsky rotation matrix appears nearly diagonal with only a few considerable off-diagonal elements. We find that the low frequency torsional motion does not make any significant contribution to the decay of the NOPF. Frequency shifts have more effect on the decay of the NOPF than the Duschinsky rotation does, but the simplest spin-boson model alone describes coherence decay quite well. At times long compared to the main Gaussian decay, we also observe an exponential decay modulated by phase recurrence, but the exponential decay is dominant only for the last 10-20% of the relaxation. The calculated coherence dissipation time arising from intramolecular vibrational motions of 3.7 A is much shorter than an estimate of the contribution to the decoherence time due to typical solvent molecules, indicating that nuclear motions in a solute molecule can have more influence on the total electronic decoherence than do solvent molecules even for a charge-transfer system such as the present case.