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Role of Torsion-Vibration Coupling in the Overtone Spectrum and Vibrationally Mediated Photochemistry of CH3OOH and HOOH
The Journal of Physical Chemistry A ( IF 2.7 ) Pub Date : 2017-11-27 00:00:00 , DOI: 10.1021/acs.jpca.7b09778
Laura C. Dzugan 1 , Jamie Matthews 2 , Amitabha Sinha 3 , Anne B. McCoy 4
The Journal of Physical Chemistry A ( IF 2.7 ) Pub Date : 2017-11-27 00:00:00 , DOI: 10.1021/acs.jpca.7b09778
Laura C. Dzugan 1 , Jamie Matthews 2 , Amitabha Sinha 3 , Anne B. McCoy 4
Affiliation
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The yield of vibrationally excited OH fragments resulting from the vibrationally mediated photodissociation of methyl hydroperoxide (CH3OOH) excited in the vicinity of its 2νOH and 3νOH stretching overtones is compared with that resulting from excitation of the molecule to states with three quanta in the CH stretches and to the state with two quanta in the OH stretch and one in the OOH bend (2νOH + νOOH). We find that the OH fragment vibrational state distribution depends strongly on the vibrational state of CH3OOH prior to photodissociation. Specifically, dissociation from the CH stretch overtones and the stretch/bend combination band involving the OH stretch and OOH bend produced significantly less vibrationally excited OH fragments compared to that produced following excitation of CH3OOH to an overtone in the OH stretch. While the absence of vibrationally excited OH photoproducts following excitation of the CH overtone is not surprising, the lack of vibrationally excited OH following excitation to the 2νOH+νOOH combination band is unexpected given that photodissociation following excitation to the lower-energy 2νOH state produces OH products in v = 1 as well as in its ground state. This trend persists even when the electronic photodissociation wavelength is changed from 532 to 355 nm and thus suggests that the observed disparity arises from differences in the nature of the initially populated vibrational states. This lack of vibrationally excited OH products likely reflects the enhanced intramolecular vibrational energy redistribution associated with the stretch/bend combination level compared to the pure OH stretch overtone. Consistent with this hypothesis, photodissociation from the stretch/bend combination level of the smaller HOOH molecule produces more vibrationally excited OH fragments compared to that resulting from the corresponding state of CH3OOH. These results are investigated using second-order vibrational perturbation theory based on an internal coordinate representation of the normal modes. Consistent with the observations, the first-order correction to the wave function shows stronger coupling of the 2νOH+νOOH state to states with torsion excitation compared to the other bands considered in this study.
中文翻译：
扭转振动耦合在CH 3 OOH和HOOH的泛音光谱和振动介导的光化学中的作用
从甲基氢过氧化物的振动介导的光解产生振动激发OH片段（CH收率3 OOH）在其2ν附近激发OH和3ν OH拉伸泛音与比较从分子状态的激发产生具有三个量子在的CH伸展和到状态具有两个量子在OH拉伸，一个在OOH弯曲（2ν OH +ν OOH）。我们发现OH碎片的振动状态分布在很大程度上取决于CH 3的振动状态光解离之前的OOH。具体而言，与将CH 3 OOH激发至OH拉伸中的泛音后产生的振动相比，与CH拉伸泛音和涉及OH拉伸和OOH弯曲的拉伸/弯曲结合带的离解产生的振动激发的OH片段明显更少。而没有振动激发OH的光化之后的CH泛音的激发并不奇怪，缺乏振动激发OH以下激发到2ν OH +ν OOH组合带是意想不到鉴于以下激发到较低能量2ν光解OH状态生产v的OH产品= 1以及处于其基态。即使当电子光解离波长从532 nm变为355 nm时，这种趋势仍然存在，因此表明观察到的差异是由于初始填充的振动状态的性质不同而引起的。与纯OH拉伸泛音相比，缺少振动激发的OH产物可能反映了与拉伸/弯曲组合水平相关的增强的分子内振动能重新分布。与此假设相一致，与较小的HOOH分子的拉伸/弯曲结合能级相比，光解离会产生更多的振动激发的OH碎片，而CH 3的相应状态却会产生更多的振动激发的OH碎片。哦 这些结果是使用二阶振动摄动理论基于正态模式的内部坐标表示来研究的。与观测相一致，2ν的第一阶校正波函数示出了更强的耦合OH +ν OOH相比在本研究中考虑的其他频带的状态到状态与扭转激励。
更新日期：2017-11-27
中文翻译：
扭转振动耦合在CH 3 OOH和HOOH的泛音光谱和振动介导的光化学中的作用
从甲基氢过氧化物的振动介导的光解产生振动激发OH片段（CH收率3 OOH）在其2ν附近激发OH和3ν OH拉伸泛音与比较从分子状态的激发产生具有三个量子在的CH伸展和到状态具有两个量子在OH拉伸，一个在OOH弯曲（2ν OH +ν OOH）。我们发现OH碎片的振动状态分布在很大程度上取决于CH 3的振动状态光解离之前的OOH。具体而言，与将CH 3 OOH激发至OH拉伸中的泛音后产生的振动相比，与CH拉伸泛音和涉及OH拉伸和OOH弯曲的拉伸/弯曲结合带的离解产生的振动激发的OH片段明显更少。而没有振动激发OH的光化之后的CH泛音的激发并不奇怪，缺乏振动激发OH以下激发到2ν OH +ν OOH组合带是意想不到鉴于以下激发到较低能量2ν光解OH状态生产v的OH产品= 1以及处于其基态。即使当电子光解离波长从532 nm变为355 nm时，这种趋势仍然存在，因此表明观察到的差异是由于初始填充的振动状态的性质不同而引起的。与纯OH拉伸泛音相比，缺少振动激发的OH产物可能反映了与拉伸/弯曲组合水平相关的增强的分子内振动能重新分布。与此假设相一致，与较小的HOOH分子的拉伸/弯曲结合能级相比，光解离会产生更多的振动激发的OH碎片，而CH 3的相应状态却会产生更多的振动激发的OH碎片。哦 这些结果是使用二阶振动摄动理论基于正态模式的内部坐标表示来研究的。与观测相一致，2ν的第一阶校正波函数示出了更强的耦合OH +ν OOH相比在本研究中考虑的其他频带的状态到状态与扭转激励。
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