Infrared spectroscopic signature of a hydroperoxyalkyl radical (•QOOH)
Infrared spectroscopic signature of a hydroperoxyalkyl radical (•QOOH)
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DOI：
10.1063/5.0076505
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发表时间：
2022-01-07
影响因子：
4.4
通讯作者：
Lester, Marsha I.
中科院分区：
文献类型：
--
作者：
Hansen, Anne S.;Bhagde, Trisha;Lester, Marsha I.
利用红外作用光谱表征了挥发性有机物氧化过程中瞬时形成的典型碳中心氢过氧烷基自由基（& BH 2;QOOH）。The&Bounce;异丁烷氧化反应中生成的QOOH自由基2-过氧化氢-2-甲基丙-1-基（2-hydroperoxy-2-methylprop-1-yl，简写为&BCH_2（CH_3）（2）COOH），是在实验室条件下由叔丁基过氧化氢（TBHP）抽氢生成的。在2950 ~ 7050 cm（-1）处观察到喷射冷却和稳定化的& BQOOH自由基的红外光谱特征，其能量低于和高于导致OH自由基和环醚产物的过渡态势垒。所观察到的&Besides; QOOH特征包括泛音OH和CH伸缩跃迁、涉及OH或CH伸缩和较低频率模式的组合带以及基频OH和CH伸缩跃迁。大多数特征来自于一个单一的振动跃迁，在10 K的转动温度下很好地模拟了能带轮廓。在每种情况下，OH产品产生的单分子衰减的振动激活的BQOOH的紫外激光诱导荧光检测。观察到的QOOH IR跃迁的非谐频率使用二阶振动微扰理论计算，2 + 1模型，重点是耦合的OH拉伸与两个低频扭转，以及最近预测的统计QOOH单分子衰变率，包括重原子隧穿。大多数观察到的振动跃迁的& BH 2;QOOH很容易区分的TBHP前体。独特的IR跃迁的& BHQOOH，包括强大的基本OH拉伸，提供了一个通用的手段检测& BHQOOH在受控的实验室和现实世界的条件下。
Infrared (IR) action spectroscopy is utilized to characterize a prototypical carbon-centered hydroperoxyalkyl radical (& BULL;QOOH) transiently formed in the oxidation of volatile organic compounds. The & BULL;QOOH radical formed in isobutane oxidation, 2-hydroperoxy-2-methylprop-1-yl, & BULL;CH2(CH3)(2)COOH, is generated in the laboratory by H-atom abstraction from tert-butyl hydroperoxide (TBHP). IR spectral features of jet-cooled and stabilized & BULL;QOOH radicals are observed from 2950 to 7050 cm(-1) at energies that lie below and above the transition state barrier leading to OH radical and cyclic ether products. The observed & BULL;QOOH features include overtone OH and CH stretch transitions, combination bands involving OH or CH stretch and a lower frequency mode, and fundamental OH and CH stretch transitions. Most features arise from a single vibrational transition with band contours well simulated at a rotational temperature of 10 K. In each case, the OH products resulting from unimolecular decay of vibrationally activated & BULL;QOOH are detected by UV laser-induced fluorescence. Assignments of observed & BULL;QOOH IR transitions are guided by anharmonic frequencies computed using second order vibrational perturbation theory, a 2 + 1 model that focuses on the coupling of the OH stretch with two low-frequency torsions, as well as recently predicted statistical & BULL;QOOH unimolecular decay rates that include heavy-atom tunneling. Most of the observed vibrational transitions of & BULL;QOOH are readily distinguished from those of the TBHP precursor. The distinctive IR transitions of & BULL;QOOH, including the strong fundamental OH stretch, provide a general means for detection of & BULL;QOOH under controlled laboratory and real-world conditions.