High-Resolution Rovibrational Spectroscopy of Jet-Cooled Phenyl Radical: The ν 19 Out-of-Phase Symmetric CH Stretch
High-Resolution Rovibrational Spectroscopy of Jet-Cooled Phenyl Radical: The ν 19 Out-of-Phase Symmetric CH Stretch
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喷射冷却苯基自由基的高分辨率旋转振动光谱：δ 19 异相对称 CH 拉伸
DOI：
10.1021/jp400702p
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发表时间：
2013
期刊：
影响因子：
--
通讯作者：
Nesbitt, David J.
中科院分区：
文献类型：
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作者：
Buckingham, Grant T.;Chang, Chih-Hsuan;Nesbitt, David J.
通过狭缝超音速放电膨胀源中的亚多普勒红外光谱研究了苯基自由基，通过≤6 MHz（0.0002 cm-1）与McMahon等人的微波基态组合差异的一致性明确确认了最高频率b2异相C-H对称拉伸振动（ν19）的归属[Astrophys. J.2003，590，L61-64]。对亚多普勒光谱中超过100个分辨的振转峰进行最小二乘分析得到沃森哈密顿量，得到精确的激发态旋转常数和振动带原点（ν0= 3071.8915（4）cm-1），这与Ellison及其同事关于Ar基质隔离研究的令人惊讶的小红移（0.9 cm-1）一致[J. Am. 2001，123，1977]。核自旋质量和惯性缺陷证实了苯基自由基的振动平均平面性和2A 1振子对称性，对转动常数的分析与由于σ C自由基中心的部分自旋再杂化引起的碳骨架的适度C2 v畸变一致。最重要的是，尽管有原子数（N= 11）和振动模式（3 N- 6 = 27），苯基自由基表现出一个非常干净的喷射冷却的高分辨率红外光谱，没有证据表明分子内振动弛豫（IVR）现象，如局域或非局域扰动，由于强耦合附近的暗态。这为高分辨率红外光谱在其他芳烃自由基体系中的应用提供了有力的支持。
Phenyl radical has been studied via sub-Doppler infrared spectroscopy in a slit supersonic discharge expansion source, with assignments for the highest frequency b2out-of-phase C–H symmetric stretch vibration (ν19) unambiguously confirmed by ≤6 MHz (0.0002 cm–1) agreement with microwave ground state combination differences of McMahon et al. [Astrophys. J.2003,590, L61–64]. Least squares analysis of over 100 resolved rovibrational peaks in the sub-Doppler spectrum to a Watson Hamiltonian yields precision excited-state rotational constants and a vibrational band origin (ν0= 3071.8915(4) cm–1) consistent with a surprisingly small red-shift (0.9 cm–1) with respect to Ar matrix isolation studies of Ellison and co-workers [J. Am. Chem. Soc.2001,123, 1977]. Nuclear spin weights and inertial defects confirm the vibrationally averaged planarity and2A1rovibronic symmetry of phenyl radical, with analysis of the rotational constants consistent with a modestC2vdistortion of the carbon backbone frame due to partial sp rehybridization of the σ C radical-center. Most importantly, despite the number of atoms (N= 11) and vibrational modes (3N– 6 = 27), phenyl radical exhibits a remarkably clean jet cooled high-resolution IR spectrum that shows no evidence of intramolecular vibrational relaxation (IVR) phenomena such aslocalornonlocalperturbations due to strongly coupled nearby dark states. This provides strong support for the feasibility of high-resolution infrared spectroscopy in other aromatic hydrocarbon radical systems.