Isomer-specific vibronic structure of the 9-, 1-, and 2-anthracenyl radicals via slow photoelectron velocity-map imaging.

Polycyclic aromatic hydrocarbons, in various charge and protonation states, are key compounds relevant to combustion chemistry and astrochemistry. Here, we probe the vibrational and electronic spectroscopy of gas-phase 9-, 1-, and 2-anthracenyl radicals (C14H9) by photodetachment of the corresponding cryogenically cooled anions via slow photoelectron velocity-map imaging (cryo-SEVI). The use of a newly designed velocity-map imaging lens in combination with ion cooling yields photoelectron spectra with <2 cm(-1) resolution. Isomer selection of the anions is achieved using gas-phase synthesis techniques, resulting in observation and interpretation of detailed vibronic structure of the ground and lowest excited states for the three anthracenyl radical isomers. The ground-state bands yield electron affinities and vibrational frequencies for several Franck-Condon active modes of the 9-, 1-, and 2-anthracenyl radicals; term energies of the first excited states of these species are also measured. Spectra are interpreted through comparison with ab initio quantum chemistry calculations, Franck-Condon simulations, and calculations of threshold photodetachment cross sections and anisotropies. Experimental measures of the subtle differences in energetics and relative stabilities of these radical isomers are of interest from the perspective of fundamental physical organic chemistry and aid in understanding their behavior and reactivity in interstellar and combustion environments. Additionally, spectroscopic characterization of these species in the laboratory is essential for their potential identification in astrochemical data

Isomer-specific vibronic structure of the 9-, 1-, and 2-anthracenyl radicals via slow photoelectron velocity-map imaging.

Polycyclic aromatic hydrocarbons, in various charge and protonation states, are key compounds relevant to combustion chemistry and astrochemistry. Here, we probe the vibrational and electronic spectroscopy of gas-phase 9-, 1-, and 2-anthracenyl radicals (C14H9) by photodetachment of the corresponding cryogenically cooled anions via slow photoelectron velocity-map imaging (cryo-SEVI). The use of a newly designed velocity-map imaging lens in combination with ion cooling yields photoelectron spectra with <2 cm(-1) resolution. Isomer selection of the anions is achieved using gas-phase synthesis techniques, resulting in observation and interpretation of detailed vibronic structure of the ground and lowest excited states for the three anthracenyl radical isomers. The ground-state bands yield electron affinities and vibrational frequencies for several Franck-Condon active modes of the 9-, 1-, and 2-anthracenyl radicals; term energies of the first excited states of these species are also measured. Spectra are interpreted through comparison with ab initio quantum chemistry calculations, Franck-Condon simulations, and calculations of threshold photodetachment cross sections and anisotropies. Experimental measures of the subtle differences in energetics and relative stabilities of these radical isomers are of interest from the perspective of fundamental physical organic chemistry and aid in understanding their behavior and reactivity in interstellar and combustion environments. Additionally, spectroscopic characterization of these species in the laboratory is essential for their potential identification in astrochemical data

Interactions between water and 1-butyl-1-methylpyrrolidinium ionic liquids.

International audienceWe report experimental results on the diffusivity of water in two ionic liquids obtained using the pulsed-gradient spin-echo NMR method. Both ionic liquids have the same cation, 1-butyl-1-methylpyrrolidinium, but different trifluoromethyl-containing anions. One has a strongly hydrophobic anion, bis(trifluoromethylsulfonyl)amide, while the second has a hydrophilic anion, trifluoromethylsulfonate. Transport of water in these ionic liquids is much faster than would be predicted from hydrodynamic laws, indicating that the neutral water molecules experience a very different friction than the anions and cations at the molecular level. Temperature-dependent viscosities, conductivities, and densities are reported as a function of water concentration to further analyze the properties of the ionic liquid-water mixtures. These results on the properties of water in ionic liquids should be of interest to researchers in diverse areas ranging from separations, solubilizing biomass and energy technologies

Vibrational and Electronic Structure of the α- and β‑Naphthyl Radicals via Slow Photoelectron Velocity-Map Imaging

Slow photoelectron velocity-map imaging (SEVI) spectroscopy has been used to study the vibronic structure of gas-phase α- and β-naphthyl radicals (C₁₀H₇). SEVI of cryogenically cooled anions yields spectra with <4 cm^–1 resolution, allowing for the observation and interpretation of congested vibrational structure. Isomer-specific photoelectron spectra of detachment to the radical ground electronic states show detailed structure, allowing assignment of vibrational fundamental frequencies. Transitions to the first excited states of both radical isomers are also observed; vibronic coupling and photodetachment threshold effects are considered to explain the structure of the excited bands

Non-Adiabatic Effects on Excited States of Vinylidene Observed with Slow Photoelectron Velocity-Map Imaging

High-resolution slow photoelectron velocity-map imaging spectra of cryogenically cooled <i>X̃</i>²<i>B</i>₂ H₂CC^– and D₂CC^– in the region of the vinylidene triplet excited states are reported. Three electronic bands are observed and, with the assistance of electronic structure calculations and quantum dynamics on ab initio-based near-equilibrium potential energy surfaces, are assigned as detachment to the ã ³<i>B</i>₂ (T₁), <i>b̃</i> ³<i>A</i>₂ (T₂), and <i>Ã</i> ¹<i>A</i>₂ (S₁) excited states of neutral vinylidene. This work provides the first experimental observation of the <i>Ã</i> singlet excited state of H₂CC. While regular vibrational structure is observed for the <i>ã</i> and <i>Ã</i> electronic bands, a number of irregular features are resolved in the vicinity of the <i>b̃</i> band vibrational origin. High-level ab initio calculations suggest that this anomalous structure arises from a conical intersection between the <i>ã</i> and <i>b̃</i> triplet states near the <i>b̃</i> state minimum, which strongly perturbs the vibrational levels in the two electronic states through nonadiabatic coupling. Using the adiabatic electron affinity of H₂CC previously measured to be 0.490(6) eV by Ervin and co-workers [<i>J. Chem. Phys.</i> <b>1989</b>, <i>91</i>, 5974], term energies for the excited neutral states of H₂CC are found to be <i>T</i>₀(<i>ã</i> ³<i>B</i>₂) = 2.064(6), <i>T</i>₀(<i>b̃</i> ³<i>A</i>₂) = 2.738(6), and <i>T</i>₀(<i>Ã</i> ¹<i>A</i>₂) = 2.991(6) eV

Electron-Transfer Dynamics for a Donor–Bridge–Acceptor Complex in Ionic Liquids

Intramolecular photoinduced electron transfer from an <i>N</i>,<i>N</i>-dimethyl-<i>p</i>-phenylenediamine donor bridged by a diproline spacer to a coumarin 343 acceptor was studied using time-resolved fluorescence measurements in three ionic liquids and in acetonitrile. The three ionic liquids have the bis­[(trifluoromethyl)­sulfonyl]­amide anion paired with the tributylmethylammonium, 1-butyl-1-methylpyrrolidinium, and 1-decyl-1-methylpyrrolidinium cations. The dynamics in the two-proline donor–bridge–acceptor complex are compared to those observed for the same donor and acceptor connected by a single proline bridge, studied previously by Lee et al. (J. Phys. Chem. C 2012, 116, 5197). The increased conformational freedom afforded by the second bridging proline resulted in multiple energetically accessible conformations. The multiple conformations have significant variations in donor–acceptor electronic coupling, leading to dynamics that include both adiabatic and nonadiabatic contributions. In common with the single-proline bridged complex, the intramolecular electron transfer in the two-proline system was found to be in the Marcus inverted regime

Encoding of vinylidene isomerization in its anion photoelectron spectrum

Vinylidene-acetylene isomerization is the prototypical example of a 1,2-hydrogen shift, one of the most important classes of isomerization reactions in organic chemistry. This reaction was investigated with quantum state specificity by high-resolution photoelectron spectroscopy of the vinylidene anions H2CCˉ and D2CCˉ and quantum dynamics calculations. Peaks in the photoelectron spectra are considerably narrower than in previous work and reveal subtleties in the isomerization dynamics of neutral vinylidene, as well as vibronic coupling with an excited state of vinylidene. Comparison with theory permits assignment of most spectral features to eigenstates dominated by vinylidene character. However, excitation of the ν6 in-plane rocking mode in H2CC results in appreciable tunneling-facilitated mixing with highly vibrationally excited states of acetylene, leading to broadening and/or spectral fine structure that is largely suppressed for analogous vibrational levels of D2CCThe experimental part of this research was funded by the Air Force Office of Scientific Research (FA9550-16-1-0097 to D.M.N.) and the Australian Research Council Discovery Project (DP160102585 to S.T.G.). M.L.W. thanks the National Science Foundation for a graduate research fellowship. Experimental data are available in the supplementary materials. Theoretical work was funded by the National Natural Science Foundation of China (91441107 to J.M.), the Air Force Office of Scientific Research (FA9550-15-1- 0305 to H.G.), and the National Science Foundation (CHE-1361121 to D.R.Y.). R.W.F. gratefully acknowledges the Department of Energy, Office of Science, Chemical Sciences Geosciences and Biosciences Division of the Basic Energy Sciences Office (DE-FG0287ER13671). W.C.L. thanks the National Science Foundation JILA Physics Frontier Center (PHY1128544), and G.B. acknowledges the Spanish Ministry of Economy and Competitiveness (EEBB-I-16-11350 and BES-2013-063562)