Ultraviolet Photodissociation of the N-Methylpyridinium Ion: Action Spectroscopy and Product Characterization

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• 作者：Christopher S. Hansen ; Benjamin B. Kirk ; Stephen J. Blanksby ; Adam J. Trevitt
• 刊名：Journal of Physical Chemistry A
• 出版年：2013
• 出版时间：October 24, 2013
• 年：2013
• 卷：117
• 期：42
• 页码：10839-10846
• 全文大小：397K
• 年卷期：v.117,no.42(October 24, 2013)
• ISSN：1520-5215

文摘

The ultraviolet photodissociation of gas-phase N-methylpyridinium ions is studied at room temperature using laser photodissociation mass spectrometry and structurally diagnostic ion鈥搈olecule reaction kinetics. The C₅H₅N鈥揅H₃⁺ (m/z 94), C₅H₅N-CD₃⁺ (m/z 97), and C₅D₅N鈥揅H₃⁺(m/z 99) isotopologues are investigated, and it is shown that the N-methylpyridinium ion photodissociates by the loss of methane in the 36鈥?00 鈥?43鈥?00 cm^鈥? (280 鈥?230 nm) region. The dissociation likely occurs on the ground state surface following internal conversion from the S₁ state. For each isotopologue, by monitoring the photofragmentation yield as a function of photon wavenumber, a broad vibronically featured band is recorded with origin (0鈥?) transitions assigned at 38 130, 38 140 and 38 320 cm^鈥? for C₅H₅N鈥揅H₃⁺ C₅H₅N-CD₃+ and C₅D₅N鈥揅H₃⁺, respectively. With the aid of quantum chemical calculations (CASSCF(6,6)/aug-cc-pVDZ), most of the observed vibronic detail is assigned to two in-plane ring deformation modes. Finally, using ion鈥搈olecule reactions, the methane coproduct at m/z 78 is confirmed as a 2-pyridinylium ion.