193-nm photodissociation of acryloyl chloride to probe the unimolecular dissociation of CH2CHCO radicals and CH2CCO

Abstract

The work presented here uses photofragment translational spectroscopy to investigate the primary and secondary dissociation channels of acryloyl chloride (CH2==CHCOCl) excited at 193 nm. Three primary channels were observed. Two C-Cl fission channels occur, one producing fragments with high kinetic recoil energies and the other producing fragments with low translational energies. These channels produced nascent CH2CHCO radicals with internal energies ranging from 23 to 66 kcal/mol for the high-translational-energy channel and from 50 to 68 kcal/mol for the low-translational-energy channel. We found that all nascent CH2CHCO radicals were unstable to CH2CH + CO formation, in agreement with the G3//B3LYP barrier height of 22.4 kcal/mol to within experimental and computational uncertainties. The third primary channel is HCl elimination. All of the nascent CH2CCO coproducts were found to have enough internal energy to dissociate, producing CH2C: + CO, in qualitative agreement with the G3//B3LYP barrier of 39.5 kcal/mol. We derive from the experimental results an upper limit of 23 +/- 3 kcal/mol for the zero-point-corrected barrier to the unimolecular dissociation of the CH2CHCO radical to form CH2CH + CO.

Infrared absorption of 3-propenonyl (⋅CH2CHCO) radical generated upon photolysis of acryloyl chloride [CH2CHC(O)Cl] in solid para-H2

“…According to Szpunar et al, the major channel upon photolysis of CH 2 CHC(O)Cl in a molecular beam at 193 nm is the fission of the C−Cl bond; all C 2 H 3 CO radicals thus produced have enough internal energy to undergo subsequent dissociation to form CH 2 CH + CO. 15 A minor channel for formation of HCl + CH 2 CCO was also observed, and all CH 2 CCO (propadienone) underwent secondary dissociation to form CH 2 C: + CO. Because energy quenching is expected to be efficient in solid p-H 2 , the primary products C 2 H 3 CO and CH 2 CCO might be stabilized under our experimental conditions; hence CH 2 CCO and three possible conformers, s-cis-CH 2 CHĊO, s-trans-CH 2 CHĊO, and ·CH 2 CHCO, of C 2 H 3 CO are the possible carriers of the newly observed lines in group X.…”

“…5 Extensive experimental investigations on CH 2 CHC(O)Cl have been conducted. These include structural and spectral studies, [6][7][8][9][10][11] pyrolysis, 12 photolysis, [13][14][15][16][17][18] and photoionization. 19 Quantum-chemical calculations were also performed to predict the enthalpy, vibrational frequencies, electronic states, and reaction paths for isomerization and dissociation of CH 2 CHC(O)Cl.…”

“…19 Quantum-chemical calculations were also performed to predict the enthalpy, vibrational frequencies, electronic states, and reaction paths for isomerization and dissociation of CH 2 CHC(O)Cl. 10,15,17,19,20 Szpunar et al employed photofragment translational spectroscopy to investigate the primary and secondary dissociation channels of CH 2 CHC(O)Cl excited at 193 nm. 15 They observed two C−Cl fission channels that produced C 2 H 3 CO with large and small kinetic energies, respectively, but the C 2 H 3 CO radicals produced in both channels had sufficient internal energy to undergo secondary decomposition so that only products C 2 H 3 + CO were detected.…”

Theoretical rate coefficients for allyl+HO2 and allyloxy decomposition

“…Thus, it is unlikely that the dominant source of CO in the experiments is from this channel. Instead, the CO probably resulted from (i) HCO decomposition and (ii) H-abstraction from acrolein to form an unsaturated acyl radical, CH 2 @CHC(@O), which decomposes to vinyl + CO [37][38][39]. Although allyl + HO 2 can go directly to allyloxy + OH via chemical activation, it is unlikely that the allyloxy fragment will have sufficient internal energy to fragment immediately on the same time scale, since the barrier for decomposition to acrolein + H is $7 kcal/ mol above allyl + HO 2 in energy.…”

Two HCl-Elimination Channels and Two CO-Formation Channels Detected with Time-Resolved Infrared Emission upon Photolysis of Acryloyl Chloride [CH2CHC(O)Cl] at 193 nm

“…Extensive experimental investigations on the photolysis of CH 2 CHC(O)Cl have been reported. 5,6,7,8,9,10 The major photodissociation channel is the fission of its C−Cl bond to produce a C 2 H 3 CO radical, which is also a crucial intermediate in reactions between O atom and propargyl (C 3 H 3 ) radical in combustion and atmospheric chemistry. 11 Szpunar et al investigated the dynamics of photodissociation of CH 2 CHC(O)Cl in a molecular beam with light at 193 nm using photofragment-translational spectroscopy.…”