IR/UV double resonant spectroscopy of the methyl radical: Determination of ν3 in the 3pz Rydberg state

Fu, Hui; Hu, Yongjun; Bernstein, E. R.

doi:10.1063/1.2135772

Cited by 20 publications

(27 citation statements)

References 43 publications

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“…The magnitude of the wavenumber separation in the CH3 spectra is consistent with the wavenumber shift of the 3 1 1 band from the 0 0 0 band reported in IR/UV double resonance studies 44 and the additional features are assigned to a sequence in the degenerate CH stretch (ν3, e′), 3 ″ ' where n′ = n″ = 1, 2, 3……”

Section: State-selective Photodissociation Of Ch3nh2 and Cd3nh2supporting

confidence: 85%

Formation of Vibrationally Excited Methyl Radicals Following State-Specific Excitation of Methylamine

2014

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The photochemistry of methylamine has been investigated following state-specific excitation of the S1 state. 2+1 resonance-enhanced multiphoton ionization was used to detect nascent methyl radical products via the 3p 2 A2″-X̃2A2″ electronic transition. Methyl radicals were formed at all photolysis wavelengths used over the range 222 -240 nm. The nascent products showed significant rotational excitation and several quanta of vibrational excitation in ν3, the degenerate C-H stretch. The partially deuterated methyl-d3-amine isotopologue yielded methyl-d3 fragments with vibrational distributions entirely consistent with those measured for the fully protiated species; no mixed isotopologues were detected.Energetic constraints require that the vibrationally excited methyl radicals be produced in conjunction with electronic ground state NH2 X̃2B1 radicals on the S0 surface, negating the previous interpretation that dissociation occurs on the upper adiabat. New ab initio calculations characterizing the C-N bond cleavage coordinate confirm the presence of a barrier to dissociation on S1 that is insurmountable at the photolysis wavelengths used in this work. We propose a "semi-direct" mechanism in which frustrated aminyl H-atom loss on the upper adiabatic potential energy surface leads to internal conversion at the exitchannel conical intersection at extended N-H distance on its return. It is proposed that C-N bond cleavage then occurs promptly and non-statistically on the S0 surface.

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Section: State-selective Photodissociation Of Ch3nh2 and Cd3nh2supporting

confidence: 85%

Formation of Vibrationally Excited Methyl Radicals Following State-Specific Excitation of Methylamine

2014

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“…Azomethane (CH 3 NNCH 3 ), a gas at room temperature, has been used as a thermal source of methyl radicals . The kinetics of its decomposition closely mirror those for 2‐methoxyfuran, with some experiments suggesting a faster rate of decomposition and others a slower rate.…”

Section: Computational Resultsmentioning

confidence: 99%

A Quantum Chemical Study of the Abnormal Reactivity of 2‐Methoxyfuran

Simmie

Somers

Yasunaga

et al. 2013

Int J of Chemical Kinetics

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The gas-phase pyrolytic and oxidative chemistry of furans has received much attention recently because of their potential as platform chemicals and biofuels. Typically these compounds exhibit very strong ring carbon to H or CH 3 bonds. 2-Methoxyfuran had been reported to be exceptionally unstable in comparison to related substituted heterocycles in pyrolytic experiments. The origins of its reactivity are shown to be due to the very weak O-CH 3 , which at 189.5 ± 1.9 kJ mol −1 is some 200 kJ mol −1 weaker than C-H bonds in the molecule. We show that the reported reactivity is somewhat overestimated but that does not alter the fact that 2-methoxyfuran is exceptionally unstable. It may prove to be a useful alternative to azomethane as a thermal source of methyl radicals. C

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“…Acetone has a large absorption cross section at 193 nm, ϳ 10 −17 cm 2 . Dissociation of acetone at 193 nm produces only the methyl radical and CO. 21,22 Sample contact time in the quartz tube is estimated between 50 and 100 s. 23 O 2 concentration is as high as 30%, which is sufficient to assure rapid conversion of CH 3 to CH 3 OO ͓reaction ͑5͔͒.…”

Section: A Generation Of Alkyl Peroxy Radicalsmentioning

confidence: 99%

Generation and detection of alkyl peroxy radicals in a supersonic jet expansion

Bernstein

2006

The Journal of Chemical Physics

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Alkyl peroxy radicals are synthesized in a supersonic jet expansion by the initial production of alkyl radicals and subsequent reaction with molecular oxygen. Parent ions CH3OO+/CD3OO+ are observed employing vacuum ultraviolet (VUV) single photon ionizationtime-of-flight mass spectroscopy (TOFMS). Employing infrared (IR) + VUV photofragmentation detected spectroscopy, rotationally resolved infrared spectra of jet-cooled CH3OO and CD3OO radicals are recorded for the A 2A' <-- X 2A" transition by scanning the IR laser frequency while monitoring the CH3 + and CD3 + ion signals generated by the VUV laser. The band origins of the A 2A'<--X 2A" transition for CH3OO and CD3OO are identified at 7381 and 7371 cm(-1), respectively. Rotational simulation for the CH3OO and CD3OO 0(0) 0 transitions of A<--X yields a rotational temperature for these radicals of approximately 30 K. With the aid of ab initio calculations, two and five vibrational modes for the A 2A' excited electronic state are assigned for CH3OO and CD3OO radicals, respectively. Both experimental and theoretical results suggest that the ground electronic state of the ions of ethyl and propyl peroxy radicals are not stable although their ionization energies (IE) are less than 10.5 eV. The C2H5OO+/C3H7OO+ cations can readily decompose to C2H5 +/C3H7 + and O2. This is partially responsible for the inability of IR+VUV photofragmentation spectroscopy to detect the near IR A<--X electronic transition for these radicals.

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IR/UV double resonant spectroscopy of the methyl radical: Determination of ν3 in the 3pz Rydberg state

Cited by 20 publications

References 43 publications

Formation of Vibrationally Excited Methyl Radicals Following State-Specific Excitation of Methylamine

Formation of Vibrationally Excited Methyl Radicals Following State-Specific Excitation of Methylamine

A Quantum Chemical Study of the Abnormal Reactivity of 2‐Methoxyfuran

Generation and detection of alkyl peroxy radicals in a supersonic jet expansion

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