Photolysis of Ketene at 193 nm and the Rate Constant for H + HCCO at 297 K

Abstract

The 193 nm photolysis of ketene was studied by measuring the amount of atomic hydrogen produced when very dilute ketene/Ar and ketene/H 2 mixtures were irradiated by a single pulse from an ArF excimer laser. Absolute concentrations of atomic hydrogen were monitored over a time interval of 0-2.5 ms by using Lyman-R atomic resonance absorption spectroscopy (ARAS). Four different photodissociation channels of ketene were identified: H 2 CCO + hν gives (a) CH 2 ( 3 B 1 ) + CO; (b) CH 2 ( 1 A 1 ) + CO; (c) HCCO + H; and (d) C 2 O(b 1 Σ + ) + H 2 . The quantum yields for each channel were measured as φ a ) 0.628, φ b ) 0.193, φ c ) 0.107, and φ d ) 0.072, respectively. To explore the secondary chemistry that occurred when using higher pressure H 2 CCO/Ar mixtures, a mechanism was constructed that used well-documented reactions and, for most processes, rate constants that had already been accurately determined. Modeling studies using this mechanism showed the [H] profile to be determined largely by the rate of the reaction H + HCCO f CH 2 + CO. An excellent fit to all of the experimental data was obtained when k 2 ) (1.7 ( 0.3) × 10 -10 cm 3 molecule -1 s -1 .

Photochemistry and Vibrational Spectroscopy of the Trans and Cis Conformers of Acetic Acid in Solid Ar

“…This behavior is in agreement with the fact that ketene can also be photolyzed with 193-nm radiation. 43 The estimated CO:CD 2 dCdO ratio is ∼20:1, even in the earlier stages of photolysis. This means that the photolysis channel leading to production of ketene is minor or its formation rate is comparable with its decomposition in the present experimental conditions.…”

Absolute Rate Coefficient of the HCCO + NO Reaction over the Range T = 297−802 K

“…14 Of these reactions, those involving the ketenyl radical, HCCO, play a central role, 14 particularly the rapid reaction of ketenyl with atomic hydrogen, 15,16 which leads to highly reactive CH 17 and CH 2 (ã 1 A 1 ); 18 These radicals are known to undergo rapid reactions with many hydrocarbons, notably C 2 H 2 , [19][20][21][22] leading to higher unsaturated hydrocarbons, which are the building blocks of polycyclic aromatic hydrocarbons. 23,24 In combustion, HCCO is formed mainly by oxidation of ethyne, [25][26][27][28][29] and thought to be removed mainly by reaction with O 2 , H, O, OH, and NO.…”

Kinetics of HCCl + NOx reactions

“…Most of the methylene radicals are formed in the triplet ground state, and a small (<0.1) yield of CCO radicals was also observed [22]. In our calibration, typical conditions were 70 mTorr of CH 2 CO, 0.…”

“…Channel (4a) is the major product, with φ 4a = 0.81, and φ 4b = 0.11 [22]. Most of the methylene radicals are formed in the triplet ground state, and a small (<0.1) yield of CCO radicals was also observed [22].…”

“…An alternative approach was therefore used: Ketene (CH 2 CO) molecules were photolyzed at 193 nm. Although the dissociation of ketene at this wavelength is somewhat complicated, two products dominate [21,22]:…”