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Research is presented demonstrating that the lowest frequency Raman (molecular) vibrations of known fullerenes are quadrupolar in nature, and can be rationalized in terms of the 5-fold degenerate Dg oscillation of an isotropic spherical shell.

Research is presented describing the use of Raman spectroscopy to demonstrate that all fullerene cages have monopolar breathing vibrations.

The synthesis and analysis of the furanoid- (C120, C130) and the bisfuranoid-linked (C120O2) fullerene cages are presented. The compounds were prepared by the solid-state reaction between C60O and C70. Three isomers were isolated for C130O. The results of Raman spectrocopy showed that thec compounds were solids with microcrystalline structures. Semiempirical calculations of ground state energetics and vibrational frequencies were also performed.

A photodissociation study of metastable tetraanionic phthalocyanine molecules isolated in a Penning trap is reported. The experimental setup is described in detail and measurements are performed which indicate that electronic spectroscopy can be routinely performed at a reasonable duty cycle.

Spontaneous electron loss from Ni(Pc (SO3) sub 4) (super 4-) and Cu(Pc(SO3) sub 4 (super 4-) studied in a UHV Penning trap at ambient temperature is described. The electron detachment energy should be lower for the C (sub 2v) isomer than for the other isomers.

We have observed that C60+ ions isolated in cryogenic matrices show distinct near-IR photoluminescence upon excitation in the near-IR range. By contrast, UV photoexcitation does not lead to measurable luminescence. Near-IR C60+ photoluminescence is a one-photon process. The emission is mainly concentrated in one band and corresponds to ²A1u ← ²E1g relaxation. We present experimental data for the Stokes shift, power, and temperature dependencies as well as the quantum efficiency of the photoluminescence. Our findings may be relevant for astronomy, considering recent unequivocal assignment of five diffuse interstellar bands to near-IR absorption bands of C60+. [ABSTRACT FROM AUTHOR]

We compare the intersystem crossing rate, k ISC , of Rose Bengal (RB) in an aqueous pH 12 solution with the corresponding relaxation rates of four different RB-derived anion and dianion species isolated in the gas phase: the doubly deprotonated dianion ([RB-2H] 2- ), the singly deprotonated monoanion ([RB-H] - ), and the corresponding singly negatively charged sodium and cesium adducts ([RB-2H + Na] - and [RB-2H + Cs] - , respectively). Each of them was probed following photoexcitation of their first singlet excited states (S 1 ) at or near room temperature. The solution was studied by transient absorption spectroscopy, whereas the mass-selected anions were characterized by time-resolved photoelectron spectroscopy─all with ca. 50 femtosecond temporal resolution. [RB-H] - shows an S 1 lifetime of ca. 80 ps; the solution ensemble, thought to consist primarily of solvated dianion chromophores, shows a similar lifetime of ca. 70 ps. By contrast, the isolated dianion, [RB-2H] 2- , has a much longer lifetime. Superimposed on S 1 decay attributable mainly to intersystem crossing, all four isolated anions also show some rapid oscillatory features of the transient photoelectron signal on a 4-5 ps timescale after excitation. Interestingly, an analogous phenomenon is also seen in the transient absorption measurements. We attribute it to a librational oscillation as the S 1 state, initially populated in the S 0 geometry, relaxes into its excited state equilibrium structure. Some implications of these observations for RB photophysics and interpretation of solution measurements are discussed─also in terms of density functional theory and time-dependent density functional theory calculations of ground and excited states.

The structures of platinum cluster anions P t 6 - - P t 13 - have been investigated by trapped ion electron diffraction. Structures were assigned by comparing experimental and simulated scattering functions using candidate structures obtained by density functional theory computations, including spin-orbit coupling. We find a structural evolution from planar structures ( P t 6 - , P t 7 - ) and amorphous-like structures ( P t 7 - - P t 9 - ) to structures based on distorted tetrahedra ( P t 9 - - P t 11 - ). Finally, P t 12 - and P t 13 - are based on hcp fragments. While the structural parameters are well described by density functional theory computations for all clusters studied, the predicted lowest energy structure is found in the experiment only for P t 6 - . For larger clusters, higher energy isomers are necessary to obtain a fit to the scattering data.

We present a study of the structural evolution of tantalum cluster anions Ta n - , 6 ≤ n ≤ 13 using a combination of trapped ion electron diffraction (TIED) experiments with a variety of electronic structure methods. A genetic algorithm has been employed to establish a set of likely structures for each cluster, their geometries and energetics have been studied by density functional theory (DFT), random phase approximation, and two-component (2C) DFT methods, which include spin-orbit coupling. We find octahedral structures for Ta 6 - and Ta 8 - as well as structures based on the pentagonal bipyramid (Ta 7 - and Ta 9 - ). Ta 10 - -Ta 12 - are defective icosahedral structures and Ta 13 - is a distorted icosahedron. For most clusters, we find a good agreement between the theoretically predicted ground-state structures, especially those determined by the 2C method and the TIED results.

A series of cationic molecular fragments (C n + , n = 11, 12, 15, 16, 18, and 21), produced by electron-impact ionization of C 60 in the gas phase, were each mass-selected and accumulated in cryogenic Ne matrices. Optical absorption measurements in the UV-vis and IR spectral ranges reveal linear carbon chain structures. In particular, we have observed the known electronic transitions of linear C 11 , C 15 , and C 21 . The NIR transitions of linear C 15 - , C 16 - , and C 18 - have also been detected, indicating that soft-landing of the corresponding cations can also involve charge-changing. Newly observed electronic absorptions at 410.3 and 429.9 nm have been assigned to linear C 18 absorptions at 438.2, 443.5, 422.3, and 433.7 nm, to linear C 15 + , and absorption at 395.5 nm, to linear C 16 . Increasing deposition energy leads to fragmentation upon impact. This is indicated by absorptions of C 10 (313, 316.3 nm), when depositing C n + ( n = 11, 15, 16) as well as C 12 (332 nm) or C 14 (347.4, 356.6 nm), when depositing C 15 + or C 16 + , respectively. These were previously assigned to cyclic isomers. We reassign them to linear isomers here on the basis of plausibility arguments. The observations have been supported by time-dependent density functional theory calculations for ring and chain isomers of C n +/-/0 , 10 ≤ n ≤ 20 up to the vacuum-UV range. The electronic absorptions of carbon chains are at least 1 order of magnitude stronger than all NIR electronic absorptions of C 60 + , which have recently been attributed to several of the diffuse interstellar bands. Considering that fullerene multifragmentation yields long carbon chains that have very strong absorptions both in the UV-vis and IR spectral regions, these systems appear to be good candidates to be observed in regions of space containing fullerenes.

We have observed that C 60 + ions isolated in cryogenic matrices show distinct near-IR photoluminescence upon excitation in the near-IR range. By contrast, UV photoexcitation does not lead to measurable luminescence. Near-IR C 60 + photoluminescence is a one-photon process. The emission is mainly concentrated in one band and corresponds to 2 A 1u ← 2 E 1g relaxation. We present experimental data for the Stokes shift, power, and temperature dependencies as well as the quantum efficiency of the photoluminescence. Our findings may be relevant for astronomy, considering recent unequivocal assignment of five diffuse interstellar bands to near-IR absorption bands of C 60 + .

Although the sequencing of protonated proteins and peptides with tandem mass spectrometry has blossomed into a powerful means of characterizing the proteome, much less effort has been directed at their deprotonated analogues, which can offer complementary sequence information. We present a unified approach to characterize the structure and intermolecular interactions present in the gas-phase pentapeptide leucine-enkephalin anion by several vibrational spectroscopy schemes as well as by ion-mobility spectrometry, all of which are analyzed with the help of quantum-chemical computations. The picture emerging from this study is that deprotonation takes place at the C terminus. In this configuration, the excess charge is stabilized by strong intramolecular hydrogen bonds to two backbone amide groups and thus provides a detailed picture of a potentially common charge accommodation motif in peptide anions.

The photophysics of chromophores is strongly influenced by their environment. Solvation, charge state, and adduct formation significantly affect ground and excited state energetics and dynamics. The present study reports on fluorescence emission of rhodamine B cations (RhBH + ) and derivatives in the gas phase. Substitution of the acidic proton of RhBH + by alkali metal cations, M + , ranging from lithium to cesium leads to significant and systematic blue shifts of the emission. The gas-phase structures and singlet transition energies of RhBH + and RhBM + , M = Li, Na, K, Rb, and Cs, were investigated using Hartree-Fock theory, density functional methods, second-order Møller-Plesset perturbation theory, and the second-order approximate coupled-cluster model CC2. Comparison of experimental and theoretical results highlights the need for improved quantum chemical methods, while the hypsochromic shift observed upon substitution appears best explained by the Stark effect due to the inhomogeneous electric field generated by the alkali ions.

We present structures and photoelectron spectra of Mn(III) and Cu(II) meso-tetra(4-sulfonatophenyl)porphyrin (TPPS) multianions, as well as of homomolecular dimers and trimers thereof. The structural assignments are based on a combination of mass spectrometry, ion mobility measurements, and semiempirical as well as density functional theory (DFT) calculations. Depending on the type of central metal atom, two completely different dimer structural motifs are found. With a central Mn(III), the monomeric units are connected via sulfonic-acid-manganese bonds resulting in a tilted stack arrangement of porphyrin rings. With Cu(II) as the central atom, the sulfonic acid groups preferentially bind to the sodium counterions, resulting in a flat dimer structure with coplanar porphyrins. Photoelectron spectra were recorded for monomers, dimers, and trimers, each in a number of different negative charge states as determined by protonation degree (+nH). In some cases, e.g., [Cu(II)TPPS](4-), [(Mn(III)TPPS)2 + H](5-), and [(Mn(III)TPPS)3 + 3H](6-), we observe electron detachment energies close to zero, or even slightly negative. In all cases, we find a large repulsive Coulomb barrier. The observed trends in detachment energies can be interpreted in terms of a simple electrostatic model.

We present gas-phase dispersed photoluminescence spectra of europium(III) 9-hydroxyphenalen-1-one (HPLN) complexes forming adducts with alkali metal ions ([Eu(PLN)3M](+) with M = Li, Na, K, Rb, and Cs) confined in a quadrupole ion trap for study. The mass selected alkali metal cation adducts display a split hypersensitive (5)D0 → (7)F2 Eu(3+) emission band. One of the two emission components shows a linear dependence on the radius of the alkali metal cation whereas the other component displays a quadratic dependence thereon. In addition, the relative intensities of both components invert in the same order. The experimental results are interpreted with the support of density functional calculations and Judd-Ofelt theory, yielding also structural information on the isolated [Eu(PLN)3M](+) chromophores.

C60(+) ions were produced by electron-impact ionization of sublimed C60, collimated into an ion beam, turned 90° by an electrostatic deflector to separate them from neutrals, mass filtered by a radio frequency quadrupole, and co-deposited with Ne on a cold 5 K gold-coated sapphire substrate. Infrared absorption spectroscopy revealed the additional presence of C60 and C60(-) in the as-prepared cryogenic matrixes. To change the C60(+)/C60(-) ratio, CCl4 or CO2 electron scavengers were added to the matrix gas. Also taking into account DFT calculations, we have identified nine new previously unpublished IR absorptions of C60(+) and seven of C60(-) in Ne matrixes. Our measurements are in very good agreement with DFT calculations, predicting D5d C60(+) and D3d C60(-) ground states. The new results may be of interest regarding the presence of C60 and C70 (as well as ions thereof) in Space.

The near-infrared (NIR) polymethine dye Styryl-13 emitting at approximately 925 nm has recently been suggested as a reference fluorophore for determining the quantum yield (QY) of the NIR photoluminescence of dispersed single-walled carbon nanotubes (SWNTs). Ju et al. reported the QY for SWNTs to be as high as 20% on the basis of 11% QY for Styryl-13 in methanol (Science 2009, 323, 1319). We directly compared the fluorescence of Styryl-13 and Styryl-20 (emitting at approximately 945 nm) with that of the standard fluorophore Rhodamine 6G using a spectrometer with a broad visible-NIR detection range. QYs of 2.0 (4.5) and 0.52 (0.80)% were determined for Styryl-13 and Styryl-20 in methanol (propylene carbonate), respectively. Correspondingly, the above-mentioned photoluminescence efficiency of SWNTs appears to be strongly overestimated. We also discuss singlet oxygen as an alternative NIR reference. A total QY of 1.4% was measured for the emission of singlet oxygen at 1275 nm, as photosensitized by C70 fullerene in air-saturated carbon tetrachloride.