Molecular-beam experiments for photodissociation of propenal at 157 nm and quantum-chemical calculations for migration and elimination of hydrogen atoms in systems C3H4O and C3H3O

Abstract

We investigated the dynamics of photodissociation of propenal (acrolein, CH(2)CHCHO) at 157 nm in a molecular beam and of migration and elimination of hydrogen atoms in systems C(3)H(4)O and C(3)H(3)O using quantum-chemical calculations. Compared with the previous results of photodissociation of propenal at 193 nm, the major difference is that the C(3)H(3)O fragment present at the 193-nm photolysis disappears at the 157-nm photolysis whereas the C(3)H(2)O fragment absent at 193 nm appears at 157 nm. Optimized structures and harmonic vibrational frequencies of molecular species with gross formula C(3)H(2-4)O were computed at the level of B3LYP/6-311G(d,p) and total energies of those molecules at optimized structures were computed at the level of CCSD(T)/6-311+G(3df,2p). Based on the calculated potential-energy surfaces, we deduce that the C(3)H(3)O fragment observed in the photolysis of propenal at 193 nm is probably CHCCHOH ((2)A") and/or CH(2)CCOH ((2)A") produced from an intermediate hydroxyl propadiene (CH(2)CCHOH) following isomerization. Adiabatic and vertical ionization potentials of eight isomers of C(3)H(3)O and two isomers of C(3)H(2)O were calculated; CHCCHOH ((2)A") and CH(2)CCOH ((2)A") have ionization potentials in good agreement with the experimental value of ∼7.4 eV. We also deduce that all the nascent C(3)H(3)O fragments from the photolysis of propenal at 157 nm spontaneously decompose mainly to C(2)H(3) + CO and C(3)H(2)O + H because of the large excitation energy. This work provides profound insight into the dynamics of migration and elimination of hydrogen atoms of propenal optically excited in the vacuum-ultraviolet region.

Multiplexed Photoionization Mass Spectrometry Investigation of the O(3P) + Propyne Reaction

“…49 Table 2). 56 It is clear that none of the AIE values reported by Chin et al match the observed onset of signal at 9.1 eV in the present work. However, Chin et al considered only transitions to singlet cation states and reported difficulties finding a minimum for the energetically lowest-lying singlet methylketenyl cation (CH 3 CCO + ), as calculations instead converged to a CH 2 CHCO + structure.…”

Combination Reactions of Propargyl Radical with Hydroxyl Radical and the Isomerization and Dissociation of trans-Propenal

“…In addition, two other isomerization processes arising from IS1-cis to IS4 (CH 2 CHCOH) and IS9 (CHCHCHOH) can also take place via transition states T1/4 and T1/9 with relative energies of −24.78 and −14.48 kcal/mol, respectively. These two processes were not investigated previously in the studies of Lee and co-workers − as well as Sharath et al It is straightforward to see that IS4 is created when H atom moves from CH group to the C-centered atom, while an H-shift from CH 2 group to that carbon will form IS9. Although three species IS5-trans (−107.65 kcal/mol), IS4 (−52.73 kcal/mol), and IS9 (−29.99 kcal/mol) are generated from IS1-cis with the same mechanisms, the first one is formed more easily than the other ones due to the relative energy of T1/5 is lower than that of T1/4 as well as T1/9.…”

“…All geometric structures involved in the C 3 H 3 + OH system including reactants, intermediate states, transition states, and products optimized at the M06-2X/aug-cc-pVTZ level of theory are exhibited in Figure 3S in the SI file. Energies of all species (intermediate/transition states and products) relative to the reactants calculated at the CCSD­(T)/CBS//M06-2X/aug-cc-pVTZ+ZPE level have been compared against those predicted by Lee and co-workers − at the CCSD­(T)/6-311+G­(3df,2p)//B3LYP/6-311G­(d,p) level and the experimental data as well as data from NIST (), as shown in Table 1S. It is easy to see that there is a good agreement between our computed results and the literature data, e.g., the calculated enthalpy changes of reaction pathways giving products P4 (C 2 H 4 + CO), P5 (C 2 H 2 + HCHO), P8 (C 2 H 3 + HCO), P10 (CH 2 CHCO + H), and P12 (C 2 H 2 + CO + H 2 ) are −107.88, −64.07, −12.52, −18.49, and −66.55 kcal/mol, respectively, which agree closely with the experimental values of −104.68, −62.38, −10.88, −20.38, and −64.58 kcal/mol, respectively; the maximum deviation between our results and experimentally reported data of those product channels is 3.2 kcal/mol which is considered to be a regular deviation of the available calculational methodology (see Table 1S).…”

“…Many experimental and theoretical studies − were performed by the photolysis and quantum chemical predictions relied on the ground and excited-state potential energy surfaces of cis-/trans-propenal (CH 2 CHCHO), an intermediate state which can be created from the C 3 H 3 + OH reaction. Specifically, in the 308–473 K temperature range and pressures ranging from 1 to 64 Torr, C 2 H 3 + HCO and C 2 H 4 + CO were considered to be major decomposition paths of propenal at internal energy (IE) of ∼91 kcal/mol given by Coomber and Pitts, while four product pairs of CH 2 CH + HCO, CH 2 CHCO + H, CH 2 CH 2 + CO, and CH 3 CH + CO were confirmed to be favorable dissociation channels of propenal in the IE range from 85.6 to ∼91 kcal/mol reported by Gardner et al The HCO appearance rate was experimentally determined by employing laser-induced fluorescence based on the photodissociation of propenal at ∼95 kcal/mol published by Jen and Chen .…”

“…This reaction path will also be clarified in the current study. Lee and co-workers − established mechanisms for the isomerization/dissociation reactions of propenal utilizing photofragment translational spectroscopy and selective VUV as well as the CCSD­(T)/6-311+G­(3df,2p)//B3LYP/6-311G­(d,p) quantum-chemical method. Microcanonical RRKM and VTST rate constants for the channels involved were also predicted, followed by the branching ratio evaluations for products of the ground state potential-energy surface.…”