Single-photon and resonance-enhanced multiphoton threshold ionization of the allyl radical

Abstract

Pulsed-field-ionization zero-kinetic-energy photoelectron spectra of jet-cooled allyl radical (C3H5) have been recorded following single-photon and resonant multiphoton excitation. Simulations based on an orbital ionization model and rovibronic photoionization selection rules reliably describe the observed intensity distributions in the photoelectron spectra obtained from single-photon excitation from the ground state and resonant multiphoton excitation via the 3s and the 3p Rydberg states. More than 30 transitions to vibrational levels of the cation were identified and assigned on the basis of predictions from ab initio calculations.

Exploring the Excited-State Dynamics of Hydrocarbon Radicals, Biradicals, and Carbenes Using Time-Resolved Photoelectron Spectroscopy and Field-Induced Surface Hopping Simulations

“…Comparing the IEs, the value for the allyl radical (8.1309 eV 106 ) is as expected about 1.60 eV lower than the one of propene (IE=9.73 eV 107 ). The additional methyl group lowers the IE once more by at least 0.3 eV (2MA: 7.88 eV, E-1MA: 7.48 eV, Z-1MA: 7.59 eV) 94 .…”

Vibronic structure of the 3s Rydberg state of the 2-methylallyl radical

“…The very sharp rise of the PIE curves and the fact that only a single band is visible in the PFI-ZEKE photoelectron spectra together with the different ionization energies strongly suggests that the bands visible in the 1+1 REMPI spectrum correspond to vibronically allowed transitions to the 3s Rydberg state in 2-methylallyl. This is similar to the allyl radical, where the 3s Rydberg state also has a geometry that is very similar to that of the cationic ground state leading to Dm = 0 transitions that are particularly intense in the PFI-ZEKE photoelectron spectra [10]. The wave numbers of several vibrational levels of the C 4 D 7 cation inferred from the PIE curves are listed in Table 5 and they generally agree to within the estimated experimental uncertainty to the predictions made at the HCTH147/TZ2P level of theory, see also Table 2.…”

“…We recently investigated the vibronic structure of the allyl radical in the energy range of its 3s Rydberg state [10,11], which is expected to have a similar electronic structure as the 2-methylallyl radical. The prominent and complex vibronic structure observed following one-photon excitation was shown to arise from vibronically allowed transitions to the e Bð 2 A 1 Þ 3s Rydberg state and transitions to the e C ð 2 B 2 Þ 3p y Rydberg and the short-lived e Eð 2 B 1 Þ 3p x Rydberg state with no evidence for transitions to valence excited states.…”

Photoionisation of the tropyl radical

“…Ionisation energies have been determined from vibrationally resolved photoelectron spectra for several open-shell species ranging from allyl [22] and propargyl [23] to indenyl (C 9 H 7 ) [24], cyclopropenylidene [25] and fulvenallenyl [26]. In the case of allyl [27–28] and propargyl [29] they are in excellent agreement with high-resolution laser studies. Such data are important for the derivation of bond dissociation energies and heats of formation of radicals, but also aid in the in situ detection of radicals in flames by photoionisation [30].…”