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首页> 外文期刊>The Journal of Chemical Physics >Bond-selective photofragmentation of jet-cooled HOD at 193 nm: Vibrationally mediated photochemistry with zero-point excitation
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Bond-selective photofragmentation of jet-cooled HOD at 193 nm: Vibrationally mediated photochemistry with zero-point excitation

机译：射流冷却的HOD在193 nm处的键选择性光碎裂：零点激发的振动介导的光化学

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Photofragment yields are reported for supersonically cooled H2O, D2O, and HOD via one photon, 193 nm photolysis in a slit jet expansion, with OH and OD fragments monitored by laser induced fluorescence methods. Detailed analysis of the dependence of OH vs OD photofragment signals on isotopic composition is used to extract relative photolysis cross sections and branching ratios for bond-selective cleavage in HOD, H2O, and D2O samples. Specified relative to the 193 nm cross sections for H2O --> H + OH, the ratios are 0.392(20), 0.032(20), and 0.0157(19) for (i) HOD --> H + OD, (ii) HOD --> D + OH and D2O --> D + OD channels, respectively. Specifically, these results indicate a propensity for H-OD vs D-OH bond cleavage in HOD of 12(8):1, This strong H/D isotopic selectivity reflects extreme non-Franck-Condon photolysis out of classically of forbidden regions of the ground-state wave function, i,e., bond-selective photochemistry mediated solely by zero-point vibrational excitation. However, when compared with theoretical predictions from full three-dimensional quantum scattering calculations on the ground ((X) over tilde (1)A(1)) and excited ((A) over bar B-1(1)) potential-energy surfaces (PES) of water, the observed HOD branching ratio is found to be too low by an order of magnitude. These results provide additional evidence that photodissociation of water in the extreme non-Franck-Condon region is not adequately explained by current theoretical models and suggest 1:hat contributions from other electronic surfaces may be important. (C) 1998 American Institute of Physics. [S0021-9606(98)01140-4]. [References: 31]
机译：通过狭缝射流扩展中的一个光子，193 nm光解，报道了超声冷却的H2O，D2O和HOD的光碎产率，其中OH和OD碎片通过激光诱导的荧光方法进行监测。 OH与OD光碎片信号对同位素组成的依赖性的详细分析可用于提取HOD，H2O和D2O样品中键选择裂解的相对光解截面和支化比率。相对于H2O-> H + OH的193 nm截面而言，（i）HOD-> H + OD，（ii）的比率为0.392（20），0.032（20）和0.0157（19）。 HOD-> D + OH和D2O-> D + OD通道。特别地，这些结果表明HOD中H-OD与D-OH键的断裂倾向为12（8）：1。这种强H / D同位素选择性反映了非Franck-Condon光解在经典禁区中的极端分解。基态波函数，即仅由零点振动激发介导的键选择光化学。但是，与从地面（在波浪号（1）A（1）上的（X）和激发的（B-1（1）条上的（A））在地面上进行的完整三维量子散射计算的理论预测相比）在水表面（PES）上，发现观察到的HOD支化率太低一个数量级。这些结果提供了额外的证据，即当前的理论模型无法充分解释极端非弗朗克-康登地区的水的光解离，并表明：1：其他电子表面的帽子贡献可能很重要。 （C）1998美国物理研究所。 [S0021-9606（98）01140-4]。 [参考：31]

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