Cooperative triple-proton/hydrogen atom relay in 7-azaindole(CH3OH)2 in the gas phase: remarkable change in the reaction mechanism from vibrational-mode specific to statistical fashion with increasing internal energy.
Cooperative triple-proton/hydrogen atom relay in 7-azaindole(CH3OH)2 in the gas phase: remarkable change in the reaction mechanism from vibrational-mode specific to statistical fashion with increasing internal energy.
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DOI：
10.1021/jp070359a
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发表时间：
2007-05
期刊：
影响因子：
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通讯作者：
Kenji Sakota;N. Inoue;Y. Komoto;H. Sekiya
中科院分区：
文献类型：
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作者：
Kenji Sakota;N. Inoue;Y. Komoto;H. Sekiya
7-氮杂吲哚-甲醇1：2簇合物[7 Al（CH（3）OH）2]在气相中发生了沿着氢键网络的激发态三质子/氢原子转移（ESTPT/HT）.通过对7Al（CH（3）OH）2-d（n）（n = 0-3）的共振增强多光子电离（REMPI）谱和7Al（CH（3）OH）2-d（0）的荧光激发谱的测量，研究了ESTPT/HT动力学.通过比较7Al（CH（3）OH）2-d（0）和7Al（CH（3）OH）2-d（3）在REMPI谱中电子振动带的强度比，我们得到了7Al（CH（3）OH）2-d（0）的加速因子f（a）（low）的下限，它是S（1）中电子振动态激发反应速率与零点态激发反应速率的比值。对于同相分子间伸缩振动（σ（1））及其泛音，f（a）（低）值为2.7 +/- 0.83和4.0 +/- 1.2（2 σ（1））分别在激发光谱中的181 cm（-1）和359 cm（-1）处观察到，而在228 cm（-1）处的振动（nu（2）/sigma（1）或nu（3）/sigma（1））的值为1.1 +/-0.83。因此，振动模式特定的ESTPT/HT发生在低能区（600 cm（-1））。分子内环模的激发在744 cm（-1）处的7Al的（nu（intra））显著提高了反应速率（f（a）（低）= 4.4 +/-0.98），但是对于在926 cm（-1）处的v（intra）+ sigma（1）的激发，f（a）（低）的增加并不显著（f（a）（低）= 5.0 +/-1.6），尽管激发了西格马（1）模式。这些结果表明，7Al（CH（3）OH）2-d（0）的ESTPT/HT反应直接从内能小于约600 cm（-1）的光激发态进行，但当内能较大时，反应从等能振动能重分布态进行.这显示了7Al（CH（3）OH）2中ESTPT/HT的一个显著特征：随着内能的增加，反应机理的性质从特定的振动模式转变为统计模式。7Al（CH（3）OH）2-d（0）中的氢键网络用有向图表示。这表明ESTPT/HT是合作现象的最简单的例子之一。
The 7-azaindole-methanol 1:2 cluster [7AI(CH(3)OH)2] undergoes excited-state triple-proton/hydrogen atom transfer (ESTPT/HT) along the hydrogen-bonded network in the gas phase. The measurements of the resonance-enhanced multiphoton ionization (REMPI) spectra of 7AI(CH(3)OH)2-d(n) (n = 0-3), where subscript n indicates the number of deuterium, and the fluorescence excitation spectrum of 7AI(CH(3)OH)2-d(0) allowed us to investigate the ESTPT/HT dynamics. By comparing the intensity ratios of the vibronic bands between 7AI(CH(3)OH)2-d(0) and 7AI(CH(3)OH)2-d(3) in REMPI spectra, we obtained the lower limit of an acceleration factor (f(a)(low)) of 7AI(CH(3)OH)2-d(0), which is the ratio of the reaction rate for the excitation of a vibronic state to that of the zero-point state in S(1). The f(a)(low) values are 2.7 +/- 0.83 and 4.0 +/- 1.2 for an in-phase intermolecular stretching vibration (sigma(1)) and its overtone (2sigma(1)) observed at 181 cm(-1) and 359 cm(-1) in the excitation spectrum, respectively, while that of the vibration (nu(2)/sigma(1) or nu(3)/sigma(1)) at 228 cm(-1) is 1.1 +/- 0.83. Thus, vibrational-mode-specific ESTPT/HT occurs in the low-energy region (600 cm(-1)). The excitation of an intramolecular ring mode (nu(intra)) of 7AI at 744 cm(-1) substantially enhances the reaction rate (f(a)(low) = 4.4 +/- 0.98), but the increase of f(a)(low) is not prominent for the excitation of v(intra) + sigma(1) at 926 cm(-1) (f(a)(low) = 5.0 +/- 1.6), although the sigma(1) mode is excited. These results suggest that the ESTPT/HT reaction in 7AI(CH(3)OH)2-d(0) directly proceeds from the photoexcited states with the internal energy less than approximately 600 cm(-1), but it occurs from the isoenergetically vibrational-energy redistributed states when the internal energy is large. This shows a remarkable feature of ESTPT/HT in 7AI(CH(3)OH)2; the nature of the reaction mechanism changes from vibrational-mode specific to statistical fashion with increasing the internal energy. The hydrogen-bonded network in 7AI(CH(3)OH)2-d(0) is represented by a directed graph. This shows that ESTPT/HT is one of the simplest examples of cooperative phenomena.