Kidwell Nathanael M, Mehta-Hurt Deepali N, Korn Joseph A, Sibert Edwin L, Zwier Timothy S
Department of Chemistry, Purdue University, West Lafayette, Indiana 47907-2084, USA.
Department of Chemistry and Theoretical Chemistry Institute, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
J Chem Phys. 2014 Jun 7;140(21):214302. doi: 10.1063/1.4879550.
The alkyl and aromatic CH stretch infrared spectra of inden-2-ylmethyl (I2M, C10H9) and trihydronaphthyl (THN, C10H11) radicals have been recorded under jet-cooled conditions in the ground (D0) and first electronically excited (D1) states using resonant ion-dip infrared (RIDIR) spectroscopy. Previously, the vibronic spectroscopy of a series of C10H9 and C10H11 hydronaphthyl radicals were investigated and their thermochemical properties were evaluated with isomer specificity [J. A. Sebree et al., J. Phys. Chem. A 11, 6255-6262 (2010)]. We show here that one of the m/z 129 spectral carriers characterized in that work was misidentified as 2-hydronaphthyl (2-HN) radical, appearing in a discharge of 1,2-dihydronaphthalene in close proximity to 1-hydronaphthyl radical. The D0-RIDIR spectrum in the alkyl CH stretch region positively identifies the m/z 129 isomer as I2M, whose two-color resonant two-photon ionization (2C-R2PI) spectrum was recently reported by Schmidt and co-workers [T. P. Troy et al., Chem. Sci. 2, 1755-1765 (2011)]. Here, we further characterize the I2M and THN radicals by recording their gas phase IR spectra in the alkyl and aromatic CH stretch regions, and explore the spectroscopic consequences of electronic excitation on the CH stretch absorptions. A local-mode CH stretch Hamiltonian incorporating cubic stretch-bend coupling between anharmonic CH stretches and CH2 scissor modes is utilized to describe their Fermi resonance interactions. Excellent agreement between the experimental and theoretical results facilitates the interpretation of the D0- and D1-state RIDIR spectra of I2M, revealing that upon excitation the alkyl CH stretches decrease in frequency by 70 cm(-1), while the allyl-like CH stretches experience a modest blueshift. In comparison, the photophysics of THN are strikingly different in that the IR transitions that possess vibrational motion along the CβH and CδH bonds are absent in the D1-RIDIR spectrum yet are predicted to be present from the theoretical model. Several hypotheses are considered to account for the perturbations to these vibrations.
在喷射冷却条件下，利用共振离子偶极红外（RIDIR）光谱，记录了茚-2-基甲基（I2M，C10H9）和三氢萘基（THN，C10H11）自由基在基态（D0）和第一电子激发态（D1）下的烷基和芳香族CH伸缩红外光谱。此前，对一系列C10H9和C10H11氢萘基自由基的振动光谱进行了研究，并以异构体特异性评估了它们的热化学性质[J. A. Sebree等人，《物理化学杂志A》11，6255 - 6262（2010）]。我们在此表明，该研究中表征的m/z 129光谱载体之一被错误地鉴定为2-氢萘基（2-HN）自由基，它出现在1,2-二氢萘放电中，紧邻1-氢萘基自由基。烷基CH伸缩区域的D0-RIDIR光谱明确将m/z 129异构体鉴定为I2M，其双色共振双光子电离（2C-R2PI）光谱最近由施密特及其同事报道[T. P. Troy等人，《化学科学》2，1755 - 1765（2011）]。在此，我们通过记录I2M和THN自由基在烷基和芳香族CH伸缩区域的气相红外光谱，进一步对它们进行表征，并探讨电子激发对CH伸缩吸收的光谱学影响。利用一个包含非谐CH伸缩与CH2剪刀模式之间立方伸缩-弯曲耦合的局域模式CH伸缩哈密顿量来描述它们费米共振相互作用。实验结果与理论结果的出色吻合有助于对I2M的D0态和D1态RIDIR光谱进行解释，揭示出激发后烷基CH伸缩频率降低70 cm⁻¹，而烯丙基样CH伸缩经历适度蓝移。相比之下，THN的光物理性质显著不同之处在于，在D1-RIDIR光谱中不存在沿CβH和CδH键具有振动运动的红外跃迁，但理论模型预测这些跃迁应该存在。考虑了几个假设来解释对这些振动的扰动。
