The spectroscopy and thermochemistry of phenylallyl radical chromophores

The resonant two-color two-photon ionization and laser induced fluorescence excitation spectra of the 1-phenylallyl (cinnamyl) and inden-2-ylmethyl radicals are reported. The 1-phenylallyl radical is found to fluoresce with low yield, permitting only a coarse dispersed fluorescence spectrum, while the inden-2-ylmethyl radical yields sufficient fluorescence to obtain ground-state vibrational frequencies and two-dimensional fluorescence spectra. Computed ionization energies and thermochemical properties including radical stabilization energies are reported for a range of resonance-stabilized radicals, including the phenylpropargyl, vinylpropargyl and phenylallyl radicals

THE GAS-PHASE SPECTRA OF RESONANCE-STABILIZED RADICALS AND THE RED RECTANGLE EMISSION

Author Institution: School of Chemistry, The University of Sydney, NSW 2006, AustraliaAlpha aromatic radicals may explain some of the emission features of Red Rectangle (RR), a nearby protoplanetary nebulae. Erosion of amorphous hydrogenated carbon may lead to resonance-stabilized products by breaking aliphatic side-chains to aromatic ``islands''. The resulting radicals may be excited by starlight to give rise to the characteristic emissions. As a part of the ongoing research nderline{\textbf{130}}(10), 3137 (2009).} nderline{\textbf{113}}, 10279 (2009).} and in order to investigate this hypothesis, the gas-phase excitation and emission spectra of some of these radicals have been identified in a molecular beam using laser induced fluorescence (LIF) spectroscopy. Resonance-stabilized 1-naphthylmethyl, 2-naphthylmethyl and acenaphthenyl radicals were produced from the discharge of 1-methylnaphthalene, 2-methylnaphthalene and acenaphthene precursors in argon, respectively. In order to determine the ground state vibrational energies of these species, their fluorescence bands were dispersed. The results are consistent with the Density Functional Theory (DFT) calculated ground state frequencies. As a complementary experiment, and to further confirm the identity of the spectral carriers, resonant two color two photon ionization (R2C2PI) spectra were also recorded. The origin bands of all these three molecules show up in the 5790 - 5840\,{\AA} range of the spectrum, the well-known RR emission region

Electronic Spectroscopy of the 1,3-Cyclopentadiene Cation (C₅H₆⁺)

The gas-phase electronic spectrum of the 1,3-cyclopentadiene radical cation (C₅H₆⁺) has been investigated using resonance-enhanced photodissociation of mass-selected C₅H₆⁺–Ar complexes in a tandem mass spectrometer. The D₁(²B₁) ← D₀(²A₂) band system spans the 460–620 nm range, while the D₂(²B₁) ← D₀(²A₂) band system appears between 320 and 370 nm. The band origins for the two systems are estimated to occur at 16 560 ± 25 and 27 808 ± 25 cm^–1, respectively. The D₁ ← D₀ band system exhibits a distinctive series of broad peaks, which, with the aid of molecular vibrational frequencies and geometries calculated using time-dependent density functional theory, are assigned to progressions in totally symmetric ring deformation modes. The broadening arises from the Franck–Condon activity of low-frequency out-of-plane vibrational modes, unresolved rotational contours, and possibly homogeneous lifetime broadening caused by rapid internal conversion to the ground electronic state

Excitation and Emission Spectra of Jet-Cooled Naphthylmethyl Radicals

Gas phase excitation and emission spectra of three naphthylmethyl radical chromophores are presented. These resonance-stabilized species, 1-naphthylmethyl, 2-naphthylmethyl, and α-acenaphthenyl, each possessing an sp2 carbon adjacent to a naphthalene mo

Hydroxyl Addition to Aromatic Alkenes: Resonance-Stabilized Radical Intermediates

The spectra of 1-indanyl-based resonance-stabilized radicals containing a hydroxyl group are identified in an electrical discharge containing indene and its alkylated derivatives. It is argued that such species form by addition of a discharge-nascent hydroxyl radical, formed from trace water, to the π bond on the five-membered ring of the parent molecule. The spectral carriers are identified by analysis of their excitation and emission spectra guided by the results from quantum chemical calculations. All three hydroxylated radicals are found to exhibit origin bands in the 21300 cm^–1 region: the 2-hydroxy-indan-1-yl radical at 21364 cm^–1, the 2-hydroxy-2-methyl-indan-1-yl radical at 21337 cm^–1, and the 2-ethyl-2-hydroxy-indan-1-yl radical exhibiting two origins of similar intensity at 21287 and 21335 cm^–1

Excitation Spectra of the Jet-Cooled 4‑Phenylbenzyl and 4‑(4′-Methylphenyl)benzyl Radicals

The excitation spectra of jet-cooled 4-phenylbenzyl and 4-(4′-methylphenyl)­benzyl radicals have been identified by a combination of resonant two-color two-photon ionization mass spectrometry and quantum chemical methods. Both radicals exhibit progressions in the biphenyl torsional mode, peaking near ν = 17. The lowest observed peak for 4-phenylbenzyl was observed at 18598 cm^–1 and is estimated to be the ν = 3 of the progression, while the lowest observed peak for the 4-(4′-methylphenyl)­benzyl radical was observed at 18183 cm^–1 and is possibly the origin. The spectra are discussed and compared to other biphenyl and benzyl chromophores