在狭缝超声速膨胀中丙炔基自由基（H2CCCH）的亚多普勒红外光谱。

Sub-Doppler infrared spectroscopy of propargyl radical (H2CCCH) in a slit supersonic expansion.

作者信息

Chang Chih-Hsuan, Nesbitt David J

机构信息

JILA, National Institute of Standards and Technology, University of Colorado, Boulder, Colorado 80309, USA and Department of Chemistry and Biochemistry, University of Colorado at Boulder, Boulder, Colorado 80309, USA.

出版信息

J Chem Phys. 2015 Jun 28;142(24):244313. doi: 10.1063/1.4922931.

DOI:10.1063/1.4922931

PMID:26133434

Abstract

The acetylenic CH stretch mode (ν1) of propargyl (H2CCCH) radical has been studied at sub-Doppler resolution (∼60 MHz) via infrared laser absorption spectroscopy in a supersonic slit-jet discharge expansion, where low rotational temperatures (Trot = 13.5(4) K) and lack of spectral congestion permit improved determination of band origin and rotational constants for the excited state. For the lowest J states primarily populated in the slit jet cooled expansion, fine structure due to the unpaired electron spin is resolved completely, which permits accurate analysis of electron spin-rotation interactions in the vibrationally excited states (εaa = - 518.1(1.8), εbb = - 13.0(3), εcc = - 1.8(3) MHz). In addition, hyperfine broadening in substantial excess of the sub-Doppler experimental linewidths is observed due to nuclear spin-electron spin contributions at the methylenic (-CH2) and acetylenic (-CH) positions, which permits detailed modeling of the fine/hyperfine structure line contours. The results are consistent with a delocalized radical spin density extending over both methylenic and acetylenic C atoms, in excellent agreement with simple resonance structures as well as ab initio theoretical calculations.

摘要

通过红外激光吸收光谱法，在超声速狭缝射流放电膨胀中以亚多普勒分辨率（约60兆赫兹）研究了炔丙基（H2CCCH）自由基的乙炔基碳氢键伸缩模式（ν1）。在该实验中，低转动温度（Trot = 13.5(4) K）以及缺乏光谱拥塞现象，使得能够更精确地确定激发态的谱带起源和转动常数。对于在狭缝射流冷却膨胀中主要占据的最低J态，由于未成对电子自旋导致的精细结构被完全分辨出来，这使得能够对振动激发态中的电子自旋 - 转动相互作用进行精确分析（εaa = - 518.1(1.8)，εbb = - 13.0(3)，εcc = - 1.8(3) 兆赫兹）。此外，由于亚甲基（-CH2）和乙炔基（-CH）位置的核自旋 - 电子自旋贡献，观察到超精细展宽大大超过了亚多普勒实验线宽，这使得能够对精细/超精细结构线轮廓进行详细建模。结果与延伸到亚甲基和乙炔基碳原子上的离域自由基自旋密度一致，与简单共振结构以及从头算理论计算结果非常吻合。