Time-resolved photoelectron spectroscopy of the allyl radical: The lifetimes of the ultraviolet bands

Abstract

Articles you may be interested in Gas-phase photodissociation of CH3COCN at 308 nm by time-resolved Fourier-transform infrared emission spectroscopy J. Chem. Phys. 136, 044302 (2012) We report ͓1ϩ1Ј͔ picosecond time-resolved pump-probe photoelectron spectra of the UV bands of the allyl radical. The experiments are performed in a molecular beam of allyl radicals, generated by supersonic jet flash pyrolysis. Photoelectron spectroscopy in a magnetic bottle is shown to be a suitable method for investigating the photophysics of organic radicals. Lifetimes were obtained for all vibronic bands between 250 and 238 nm previously assigned by MPI spectroscopy to the electronically excited B 2 A 1 , C 2 B 1 , and D 2 B 2 states, with values ranging from 20 ps to 9 ps. The nonradiative decay is due to internal conversion to the electronic ground state. Information on the structure of the allyl cation is deduced from the photoelectron spectrum.

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

“…The poor signal-to-noise ratio of this trace arises from the short excited state lifetime of only 12 ps for that state compared to the B -state origin that has a lifetime of 22 ps. 13 From the average wave number of these three intense cationic origin bands we obtain a value of 65 581.3͑80͒ cm −1 for the first ionization energy of the allyl radical, in excellent agreement with the value obtained from the one-photon VUV PFI-ZEKE photoelectron spectrum ͑see Sec. IV A and Ref.…”

“…Slightly higher values, ranging up to 8.15 eV, were reported in later works. [13][14][15][16] The most recent measurements of the adiabatic ionization energy of allyl carried out by pulsed-fieldionization zero-kinetic-energy ͑PFI-ZEKE͒ photoelectron spectroscopy using multiphoton 14 and single-photon excitation schemes 17,18 yielded values differing by as much as 22 meV. These measurements provided important information on the vibrational energy level structure of C 3 H 5 + .…”

The allyl radical revisited: a theoretical study of the electronic spectrum

“…It has the features of describing the vibrational structure of some of the low-lying Rydberg states of this molecule but misses a complete identification of the electronic states in the Rydberg region. The significant problems with assignment of the electronic spectrum of this simple molecule are due to the closeness in energy of the states [8]. In particular, in the Rydberg region there is an overlap with valence excited states, as we show in this Letter.…”

Excited-state decay of hydrocarbon radicals, investigated by femtosecond time-resolved photoionization: Ethyl, propargyl, and benzyl

“…This was demonstrated for the allyl radical ͑C 3 H 5 ͒, where time-resolved photoelectron spectroscopy showed that the electronically excited radicals return to the ground state surface within 20 ps or less by internal conversion in a two-step process. 8,9 Allyl subsequently dissociates, preferentially to allene+ H, following a mechanism appropriately modeled by statistical reaction theories. 10 In alkyl radicals on the other hand it is questionable whether purely statistical models can explain the observed dissociation rates: An investigation of the hydrogen atom loss from ethyl radical ͑C 2 H 5 ͒ upon excitation into the 2 2 AЈ state, nominally the 3s Rydberg state, yielded a rate constant more than four orders of magnitude slower than expected from simple RRKM calculations.…”