Excited‐State Dynamics of the 2‐Methylallyl Radical

Abstract

Radically exciting! The excited-state dynamics of the 2-methylallyl radical are studied by time-resolved photoionization. The radical, which is relevant for combustion processes, is generated by pyrolysis from the corresponding bromide. The lifetime of the electronically excited B state was measured to be 14 ps and shorter.

The gas-phase infrared spectra of the 2-methylallyl radical and its high-temperature reaction products

“…This precursor has been shown before to efficiently generate 2 at high number density. 9,11 The 1-methylallyl isomer is not produced from this precursor, as concluded from TPES. 13 The precursor was seeded in 2.0 bar of argon (mole fraction ≈ 5%) and a pulsed jet was produced using a solenoid valve (20 Hz) with a resistively heated SiC-tube (microreactor) 32 of 35 mm length, an inner diameter of 1 mm and a heated region of 8 mm, to cleave the precursor molecules.…”

“…34 A lifetime of 9.3 ps was reported for this band. 11 The width of the vibrational bands in the IR/UV spectrum is likely caused by the rotational temperature of the pyrolytically generated species and by power broadening due to the high power IR radiation. The excellent agreement with the computation (blue line) and previous work [14][15][16] proves that 2 is the only carrier of the spectrum and no isomerization takes place.…”

“…7 Furthermore, the CH + C 3 H 6 reaction could be a substantial source for C 4 H 7 radicals in the interstellar medium. 8 Unsurprisingly, numerous studies on isolated 1- and 2-MA generated mostly by pyrolysis have been reported, including resonance-enhanced multiphoton ionization (REMPI), 9,10 time-resolved spectroscopy, 11,12 photofragment spectroscopy to identify the unimolecular dissociation products 10 and threshold photoelectron spectroscopy (TPES) to obtain ionization energies (IE) of 7.88 eV (2-MA), 7.48 ( E -1-MA) and 7.59 eV ( Z -1-MA). 13 Some information on the vibrational frequencies of 2 is available from infrared spectroscopy in a rare gas matrix 14,15 and from resonance Raman spectroscopy in the gas-phase.…”

Ultrafast primary processes of the stable neutral organic radical, 1,3,5-triphenylverdazyl, in liquid solution

“…1 This is because carbon, oxygen, or nitrogen-centered radicals are generally highly reactive and their rather short ground-state lifetimes invariably preclude an in-depth spectroscopic analysis of their photoinduced processes. [2][3][4][5][6] A feature that appears to be common for most hydrocarbon radicals is a rapid non-radiative excited-state decay that is often followed by the unimolecular loss of a hydrogen atom from high-lying vibrational states in the electronic ground state. 2 In such studies, small organic radicals like ethyl, t-butyl, propargyl, benzyl, allyl, or methylallyl can be generated by flash photolysis or pyrolysis of suitably labile precursors and the primary processes following electronic excitation can be recorded in a pump-probe experiment employing e.g.…”

“…Therefore, most of our knowledge of the excited state dynamics of organic compounds with unpaired electrons stems from experiments conducted on gas phase samples or molecular beam ensembles. [2][3][4][5][6] To our knowledge, nothing is known so far about the dynamics of electronically excited neutral organic radicals in liquid solutions and the dynamical interactions with a condensed-phase solvation environment. a multi-photon ionization/mass-spectrometric detection scheme.…”