Intense, hyperthermal source of organic radicals for matrix-isolation spectroscopy

Zhang, Xu; Friderichsen, Anders V.; Nandi, Sreela; Ellison, G. Barney; David, Donald E.; McKinnon, J. Thomas; Lindeman, T. G.; Dayton, David C.; Nimlos, Mark R.

doi:10.1063/1.1574397

Cited by 83 publications

(115 citation statements)

References 63 publications

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“…We have studied the thermal cracking of CH 3 CHO in a heated microtubular (µtubular) reactor, 19,20 a 1 mm i.d. x 2 cm long SiC tube that can be heated to temperatures up to 1700 K. A dilute sample of acetaldehyde is mixed with an inert carrier gas and passed through the heated SiC tube.…”

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confidence: 99%

The products of the thermal decomposition of CH3CHO

Vasiliou

Piech

Zhang

et al. 2011

The Journal of Chemical Physics

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We have used a heated 2 cm × 1 mm SiC microtubular (μtubular) reactor to decompose acetaldehyde: CH3CHO + Δ → products. Thermal decomposition is followed at pressures of 75–150 Torr and at temperatures up to 1675 K, conditions that correspond to residence times of roughly 50–100 μs in the μtubular reactor. The acetaldehyde decomposition products are identified by two independent techniques: vacuum ultraviolet photoionization mass spectroscopy (PIMS) and infrared (IR) absorption spectroscopy after isolation in a cryogenic matrix. Besides CH3CHO, we have studied three isotopologues, CH3CDO, CD3CHO, and CD3CDO. We have identified the thermal decomposition products CH3 (PIMS), CO (IR, PIMS), H (PIMS), H2 (PIMS), CH2CO (IR, PIMS), CH2=CHOH (IR, PIMS), H2O (IR, PIMS), and HC≡CH (IR, PIMS). Plausible evidence has been found to support the idea that there are at least three different thermal decomposition pathways for CH3CHO; namely, radical decomposition: CH3CHO + Δ → CH3 + [HCO] → CH3 + H + CO; elimination: CH3CHO + Δ → H2 + CH2=C=O; isomerization/elimination: CH3CHO + Δ → [CH2=CH–OH] → HC≡CH + H2O. An interesting result is that both PIMS and IR spectroscopy show compelling evidence for the participation of vinylidene, CH2=C:, as an intermediate in the decomposition of vinyl alcohol: CH2=CH–OH + Δ → [CH2=C:] + H2O → HC≡CH + H2O.

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confidence: 99%

The products of the thermal decomposition of CH3CHO

Vasiliou

Piech

Zhang

et al. 2011

The Journal of Chemical Physics

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“…Another unexpected change involves the (spectroscopically also well founded) 16.8% increase of the C−C stretching force constant on ionization of the allyl radical. To explain that, it turns out to be judicious to consider the of f-diagonal element of the force constant matrix, which represents the interaction of the two C−C stretches.…”

Section: ■ Discussionmentioning

confidence: 99%

“…800°C in the case of allyl iodide, and 950°C in the case of benzyl iodide. The yields of radicals were optimized with the help of a time-of-flight mass spectrometer as described by Zhang et al 16 The resulting molecular beam was trapped on a CsI plate held at 10 K in a closed-cycle cryostat. IR spectra were recorded by a Bomem DA3 interferometer at 0.5 cm −1 resolution.…”

Section: ■ Materials and Methodsmentioning

confidence: 99%

Carbocations Generated under Stable Conditions by Ionization of Matrix-Isolated Radicals: The Allyl and Benzyl Cations

2013

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Carbocations are crucial intermediates in many chemical reactions; hence, considerable effort has gone into investigating their structures and properties, for example, in superacids, in salts, or in the gas phase. However, studies of the vibrational structure of carbocations are not abundant, because their infrared spectra are difficult to obtain in superacids or salts (where furthermore the cations may be perturbed by counterions), and the generation of gas-phase carbocations in discharges usually produces several species. We have applied the technique of ionizing neutral compounds by X-irradiation of cryogenic Ar matrices to radicals embedded in such matrices, thus producing closed-shell cations that can be investigated leisurely, and in the absence of counterions or other perturbing effects, by various forms of spectroscopy. This Article describes the first set of results that were obtained by this approach, the IR spectra of the allyl and the benzyl cation. We use the information obtained in this way, together with previously obtained data, to assess the changes in chemical bonding between the allyl and benzyl radicals and cations, respectively.

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“…The dosing nozzle for CH 2 Br production is the hyperthermal nozzle described elsewhere [11]. Briefly, this consists of a resistively heated 1 mm diameter SiC tube at the output of a Parker General Valve Series 9 pulsed solenoid valve (100 Hz frequency and about 1 ms pulse width).…”

Section: Methodsmentioning

confidence: 99%