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Acetaldehyde cations (CH 3 CHO + ) were prepared using single-photon vacuum ultraviolet ionization of CH 3 CHO in a molecular beam and the fragmentation dynamics explored over the photolysis wavelength range 390–210 nm using velocity-map ion imaging and photofragment yield (PHOFY) spectroscopy. Four fragmentation channels are characterized: CH 3 CHO + → C 2 H 3 O + + H (I), CH 3 CHO + → HCO + + CH 3 (II), CH 3 CHO + → CH 3 + + HCO (III), CH 3 CHO + → CH 4 + + CO (IV). Channels (I), (II), and (IV) are observed across the full photolysis wavelength range while channel (III) is observed only at λ < 317 nm. Maximum fragment ion yields are obtained at ∼250 nm. Ion images were recorded over the range 316–228 nm, which corresponds to initial excitation to the B̃ 2 A′ and C̃ 2 A′ states of CH 3 CHO + . The speed and angular distributions are distinctly different for each detected ion and show evidence of both statistical and dynamical fragmentation pathways. At longer wavelengths, fragmentation via channel (I) leads to modest translational energies ( E T ), consistent with dissociation over a small barrier and production of highly internally excited CH 3 CO + . Additional components with E INT greater than the CH 3 CO + secondary dissociation threshold appear at shorter wavelengths and are assigned to fragmentation products of vinyl alcohol cation or oxirane cation formed by isomerization of energized CH 3 CHO + . The E T distribution observed for channel (III) products peaks at zero but is notably colder than that predicted by phase space theory, particularly at longer photolysis wavelengths. The colder-than-statistical E T distributions are attributed to contributions from secondary fragmentation of energized CH 3 CO + formed via channel (I), which are attenuated by CH 3 CHO + isomerization at shorter wavelengths. Fragmentation via channels (II) and (IV) results in qualitatively similar outcomes, with evidence of isotropic statistical components at low- E T and anisotropic components due to excited state dynamics at higher E T .
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Characterizing the multi-dimensional reaction dynamics of dihalomethanes using XUV-induced Coulomb explosion imaging
Site-selective probing of iodine 4d orbitals at 13.1 nm was used to characterize the photolysis of CH2I2 and CH2BrI initiated at 202.5 nm. Time-dependent fragment ion momenta were recorded using Coulomb explosion imaging mass spectrometry and used to determine the structural dynamics of the dissociating molecules. Correlations between these fragment momenta, as well as the onset times of electron transfer reactions between them, indicate that each molecule can undergo neutral three-body photolysis. For CH2I2, the structural evolution of the neutral molecule was simultaneously characterized along the C–I and I–C–I coordinates, demonstrating the sensitivity of these measurements to nuclear motion along multiple degrees of freedom.
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- Award ID(s):
- 2309238
- PAR ID:
- 10522625
- Author(s) / Creator(s):
- ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; more »
- Publisher / Repository:
- AIP
- Date Published:
- Journal Name:
- The Journal of Chemical Physics
- Volume:
- 159
- Issue:
- 14
- ISSN:
- 0021-9606
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1063/5.0172749
