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

Abstract

The resonance-stabilized 2-methylallyl radical, 2-MA, is considered as a possible intermediate in the formation of polycyclic aromatic hydrocarbons (PAHs) in combustion processes. In this work, we report on its contribution...

IR/UV Double Resonance Study of the 2‐Phenylallyl Radical and its Pyrolysis Products

“…Two further distinct bands are identified at 767 and 786 cm −1 , originating from an out‐of‐plane wagging mode and the symmetric CH 2 out‐of‐plane bending vibration. Note, that the latter is in excellent agreement with the wavenumber of the CH 2 out‐of‐plane bending mode of the related 2‐methylallyl radical [6] . Several further bands of smaller and medium intensity are predicted in the higher wavenumber region by the computation, but are difficult to identify in the experimental spectrum due to the low S/N ratio.…”

“…Recently, we investigated the high temperature chemistry of the 2‐methylallyl [6] (2‐MA) and 1‐ and 3‐phenylpropargyl radicals [7] (1‐ and 3‐PPR) in a microreactor. While 2‐MA exhibits a methyl group instead of phenyl, PPR and 2 are composed of three C 3 units that play an important role in the formation of aromatic hydrocarbons [41] .…”

“…Hence, the spectroscopic identification of RSR and the investigation of their chemistry is of considerable interest. Here, we focus on reactions of the 2‐phenylallyl radical, 2 in Scheme 1, and compare its high temperature chemistry with the one of the related 2‐methylallyl [6] and phenylpropargyl radicals [7] . While for its isomer 1‐phenylallyl, a study of the D 1 ←D 0 transition by laser‐induced fluorescence has been reported, [8] no spectroscopic information is available so far on 2 .…”

“…It is particularly well suited for the isomer‐selective characterization of aromatic molecules and PAH, which generally absorb in the UV. Recently, we employed IR/UV spectroscopy to record IR spectra of isolated RSR with relevance to combustion and to monitor their chemical reactions, among them phenylpropargyl, [7] benzyl, [16] ortho ‐benzyne [17] and 2‐methylallyl [6] . In contrast, small molecules without a UV chromophore are difficult to detect by IR/UV, thus complementary photoionization data are helpful, as shown for the ortho ‐benzyne self‐reaction [17] .…”

Stacking Is Favored over Hydrogen Bonding in Azaphenanthrene Dimers

“…Here, we use IR/UV ion dip spectroscopy in combination with high-level quantum chemical calculations to characterize the geometry of dimers of benzo­[f]­quinoline and phenanthridine. IR/UV spectroscopy has been previously successfully applied to characterize biomolecules, − rotaxanes, and reactive intermediates. − More recently, stacked acenaphthene and naphthalene dimers and their solvated clusters were studied, − but the IR/UV approach has not yet been employed to study the competition between stacked and hydrogen-bonded structures in molecular clusters.…”