Valence Photoionization and Autoionization of the Formyl Radical

Abstract

We have used 308 nm photolysis of acetaldehyde to measure a photoionization spectrum of the formyl (HCO) radical between 8 and 11.5 eV using an 11 meV FWHM photoionization energy resolution. We have confirmed that the formyl radical is the carrier of the spectrum by generating an identical spectrum of the HCO product in the Cl + H 2 CO reaction. The spectrum of HCO and its deuterated isotopologue (DCO) have several resolved autoionizing resonances above the Franck−Condon envelope, which we assign to autoionization after initial excitation into neutral 3sσ and 3p Rydberg states converging to the first triplet excited state of HCO + (a3 A′). The quantum defects for these states are δ 3sσ = 1.06 ± 0.02 and δ 3p = 0.821 ± 0.019. We report absolute photoionization crosssection measurements of σ HCO PI (9.907 eV) = 4.5 ± 0.9 Mb, σ HCO PI (10.007 eV) = 4.8 ± 1.0 Mb, σ HCO PI (10.107 eV) = 6.0 ± 1.2 Mb, σ HCO PI (10.107 eV) = 5.7 ± 1.2 Mb, and σ HCO PI (10.304 eV) = 10.6 ± 2.2 Mb relative to the photoionization cross section of the methyl radical. The absolute cross-section measurements are a factor of ∼1.5 larger than those determined in past studies, although the presence of strong autoionizing features supports a dependence on photoionization energy resolution. We propose that the semiempirical model of Xu and Pratt for estimation of free radical photoionization cross sections is more accurate when applied with a reference species containing the same atoms as the free radical rather than isoelectronic species with different atoms.

Quantification of Key Peroxy and Hydroperoxide Intermediates in the Low-Temperature Oxidation of Dimethyl Ether

“…CHO is detectable at our ionization energies, yet we do not observe it. We cannot detect CO because doing so would require E VUV > 14 eV, where our mass spectrometer would be saturated by ion counts from O 2 .…”

Stress-Alteration Enhancement of the Reactivity of Aluminum Nanoparticles in the Catalytic Decomposition of exo-Tetrahydrodicyclopentadiene (JP-10)

“…To decipher the catalytic effects of the SA-AlNPs at the molecular level, comprehensive knowledge of the nascent products formed in the molecular beam requires a detailed analysis of distinct isomer-selective PIE curves. Overall, the identified products (Table S1, Figure ) in this study − belong to the class of closed-shell hydrocarbons, hydrocarbon radicals, and oxygenated species (Figure and Figure ) including oxygenated radicals. The detection of the oxygenated products in the absence of any external supply of molecular oxygen ensures the active surface chemistry involving the oxygen-atom transfer from the aluminum oxide layer (Al 2 O 3 ) to the JP-10 molecule, as observed in the case of the UN-AlNPs …”

Efficient Oxidative Decomposition of Jet-Fuel exo-Tetrahydrodicyclopentadiene (JP-10) by Aluminum Nanoparticles in a Catalytic Microreactor: An Online Vacuum Ultraviolet Photoionization Study

“…This is achieved through an extraction and detailed analysis of distinct PIE curves followed by a comparison with the products corresponding to the pure JP-10 pyrolysis . Overall, 63 products were identified in each of the oxidation events, − which are constituted of four major classes: (i) oxidized molecules, (ii) oxidized radicals, (iii) closed-shell hydrocarbons, and (iv) hydrocarbon radicals. Table provides an overview of these molecular classes, including their ionization energies and appearance temperature range.…”