Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan.
J Chem Phys. 2017 Jun 28;146(24):244302. doi: 10.1063/1.4986536.
The region 1273-1290 cm of the ν fundamental of the simplest Criegee intermediate, CHOO, has been measured using a quantum cascade laser transient absorption spectrometer, which offers greater sensitivity and spectral resolution (<0.004 cm) than previous works based on thermal light sources. Gas phase CHOO was generated from the reaction of CHI + O at 298 K and 4 Torr. The analysis of the absorption spectrum has provided precise values for the vibrational frequency and the rotational constants, with fitting errors of a few MHz. The determined ratios of the rotational constants, A'/A″ = 0.9986, B'/B″ = 0.9974, and C'/C″ = 1.0010, and the relative intensities of the a- and b-type transitions, 90:10, are in good agreement with literature values from a theoretical calculation using the MULTIMODE approach, based on a high-level ab initio potential energy surface. The low-K (=K) lines can be fitted extremely well, but rotational perturbations by other vibrational modes disrupt the structure for K = 4 and K ≥ 6. Not only the spectral resolution but also the detection sensitivity of CHOO IR transitions has been greatly improved in this work, allowing for unambiguous monitoring of CHOO in kinetic studies at low concentrations.
使用量子级联激光瞬态吸收光谱仪测量了最简单的 Criegee 中间体 CHOO 的 ν 基频的 1273-1290cm 区域，该光谱仪的灵敏度和光谱分辨率（<0.004cm）高于以前基于热光源的工作。气相 CHOO 是通过 CHI + O 在 298K 和 4 托下的反应产生的。吸收光谱的分析提供了振动频率和转动常数的精确值，拟合误差为几兆赫。确定的转动常数比值 A'/A″=0.9986，B'/B″=0.9974，C'/C″=1.0010，以及 a-和 b-型跃迁的相对强度 90:10，与使用 MULTIMODE 方法基于高水平从头算势能面的理论计算的文献值非常吻合。低-K（=K）线可以很好地拟合，但其他振动模式的转动微扰破坏了 K=4 和 K≥6 的结构。这项工作不仅大大提高了 CHOO IR 跃迁的光谱分辨率，而且提高了检测灵敏度，允许在低浓度下进行动力学研究时对 CHOO 进行明确监测。
