Polarized Matrix Infrared Spectra of Cyclopentadienone: Observations, Calculations, and Assignment for an Important Intermediate in Combustion and Biomass Pyrolysis

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• 作者：Thomas K. Ormond ; Adam M. Scheer ; Mark R. Nimlos ; David J. Robichaud ; John W. Daily ; John F. Stanton ; G. Barney Ellison
• 刊名：Journal of Physical Chemistry A
• 出版年：2014
• 出版时间：January 30, 2014
• 年：2014
• 卷：118
• 期：4
• 页码：708-718
• 全文大小：552K
• ISSN：1520-5215

文摘

A detailed vibrational analysis of the infrared spectra of cyclopentadienone (C₅H₄鈺怬) in rare gas matrices has been carried out. Ab initio coupled-cluster anharmonic force field calculations were used to guide the assignments. Flash pyrolysis of o-phenylene sulfite (C₆H₄O₂SO) was used to provide a molecular beam of C₅H₄鈺怬 entrained in a rare gas carrier. The beam was interrogated with time-of-flight photoionization mass spectrometry (PIMS), confirming the clean, intense production of C₅H₄鈺怬. Matrix isolation infrared spectroscopy coupled with 355 nm polarized UV for photoorientation and linear dichroism experiments was used to determine the symmetries of the vibrations. Cyclopentadienone has 24 fundamental vibrational modes, 螕_vib = 9a₁ 3a₂ 4b₁ 8b₂. Using vibrational perturbation theory and a deperturbation鈥揹iagonalization method, we report assignments of the following fundamental modes (cm^鈥?) in a 4 K neon matrix: the a₁ modes of X虄 ¹A₁ C₅H₄鈺怬 are found to be 谓₁ = 3107, 谓₂ = (3100, 3099), 谓₃ = 1735, 谓₅ = 1333, 谓₇ = 952, 谓₈ = 843, and 谓₉ = 651; the inferred a₂ modes are 谓₁₀ = 933, and 谓₁₁ = 722; the b₁ modes are 谓₁₃ = 932, 谓₁₄ = 822, and 谓₁₅ = 629; the b₂ fundamentals are 谓₁₇ = 3143, 谓₁₈ = (3078, 3076) 谓₁₉ = (1601 or 1595), 谓₂₀ = 1283, 谓₂₁ = 1138, 谓₂₂ = 1066, 谓₂₃ = 738, and 谓₂₄ = 458. The modes 谓₄ and 谓₆ were too weak to be detected, 谓₁₂ is dipole-forbidden and its position cannot be inferred from combination and overtone bands, and 谓₁₆ is below our detection range (<400 cm^鈥?). Additional features were observed and compared to anharmonic calculations, assigned as two quantum transitions, and used to assign some of the weak and infrared inactive fundamental vibrations.