Photoabsorption Spectroscopy Research Articles

Impact of side-chain length on alternating current mobility of charge carriers in regioregular poly(3-alkylthiophene) films

The charge carrier mobility in films of regioregular polythiophenes substituted by n-alkyl side-chains, of butyl, hexyl, octyl, decyl, and dodecyl, was investigated by flash-photolysis time-resolved microwave conductivity (FP-TRMC), and transient photoabsorption spectroscopy excited at 355nm. The charge carrier concentration was estimated from inspecting radical anions of perylenecarboxydiimide (PDI), which also acts as an efficient electron acceptor to improve the yield of photocarrier generation. We discuss the dependence of side-chain length in terms of decay dynamics, quantum yield of charge carrier generation, and alternating current (ca. 9GHz) mobility, which exceeded 0.12cm2/(Vs).

The vacuum UV photoabsorption spectroscopy of vinyl fluoride (C 2H 3F): The vibrational fine structure and its analysis

The vacuum UV photoabsorption spectrum of C 2H 3F has been examined in detail between 6 eV and 25 eV photon energy by using synchrotron radiation. The analysis of the data is supported by ab initio quantum mechanical calculations applied to valence and Rydberg excited states of C 2H 3F. At 7.6 eV the π → π ∗ and the 2a″ → 3s transitions are observed. An analysis is proposed and applied to the mixed fine structure belonging to these transitions. For the π → π ∗ transition one single long vibrational progression is observed with hcω e = 95 ± 7 meV (766 ± 56 cm −1) and its adiabatic excitation energy is 6.892 eV (55 588 cm −1). The 2a″ → 3s transition is characterized by a single short progression with hcω e = 167 ± 10 meV (1350 ± 80 cm −1) starting at 6.974 eV (56 249 cm −1). From the present ab initio calculations these two wavenumbers best correspond to the vibrational modes v 9 (CH 2 rock in-plane, FCC-bend) and v 6 (CH 2 rock in-plane, CF stretch) calculated at 615 cm −1 in the π ∗ state and 1315 cm −1 in the ( 2A″)3s Rydberg state respectively. The C C stretching could not be excluded. The dense structured spectrum observed between 8.0 eV and 10.5 eV has been analyzed in terms of vibronic transitions to Rydberg states all converging to the C 2 H 3 F + ( X ∼ A ″ ) ionic ground state. An analysis of the associated complex fine structure of the individual Rydberg states has been attempted providing average values of the wavenumbers, e.g., for the ( 2A″)3p Rydberg state hcω 9 = 60 ± 1 meV (or 484 ± 8 cm −1), hcω 7 = 151 ± 7 meV (or 1218 ± 60 cm −1), hcω 4 = 191 ± 3 meV (or 1540 ± 24 cm −1). The assignment of hcω = 105 ± 5 meV (or 823 ± 40 cm −1) is discussed. These experimental values are in good agreement with the theoretical predictions for C 2H 3F + [R. Locht, B. Leyh, D. Dehareng, K. Hottmann, H. Baumgärtel, Chem. Phys. (in press)]. Above 10.5 eV and up to 25 eV several broad and strong bands are tentatively assigned to transitions to valence (V–V) and/or Rydberg (V–R) states converging to excited ionic states of C 2H 3F.

Multielectron structure and dynamics in scaled-energy Stark photoabsorption and recurrence spectra

We use the $4s{[3/2]}_{2}^{o}$ metastable state of atomic argon created by charge-transfer collisions between a 5 keV ${\text{Ar}}^{+}$ beam and K vapor to perform laser scaled-energy Stark photoabsorption and recurrence spectroscopy of even-parity Rydberg states, detected by field ionization and forced autoionization, in a region of the spectrum that contains two distinct perturbations. We apply a uniform electric field that changes with the frequency of the laser to maintain a constant scaled energy relative to the first ionization limit of the atom, associated with the ion core in a ${^{2}P}_{3/2}$ configuration. Local perturbations to the Rydberg series $(15\ensuremath{\le}n\ensuremath{\le}28)$ occur due to ${n}^{\ensuremath{'}}=8$ and 10 Stark states that belong to the series converging to the second ionization threshold with the ion core in a ${^{2}P}_{1/2}$ configuration. The resulting absorption spectra show multielectron effects due to configuration interaction and angular momentum coupling. These effects have dynamical implications in the recurrence spectrum. In particular, the variations in the Stark structure of the absorption spectrum result in a recurrence spectrum that shows two prominent multielectron features. One is the presence of recurrence peaks with scaled actions less than that of the hydrogenic primitive orbit. We attribute this to excitation in which both the ion core and the Rydberg electron absorb energy during photoexcitation. The second multielectron effect observed is recurrence peaks that occur at the sum of scaled actions of the primitive orbit (and its repetitions) associated with the pair of perturbations and a hydrogenic closed classical orbit. We attribute these peaks to core-changing inelastic scattering of the Rydberg electron with the ionic core due to angular momentum coupling. For comparison, we measured the regular autoionizing Rydberg series of argon between the first and second ionization thresholds, where no perturbing resonances exist.

Application of Polymer Solubility Theory to Solution Phase Dispersion of Single-Walled Carbon Nanotubes

Single-walled carbon nanotubes below 1.5 μm in length are effectively rigid rod-like polymers, but polymer solubility theory has not yet been applied to their solution phase dispersion despite its success in modeling other polymer systems. In this work, we experimentally determine the solubility of arc discharge single-walled carbon nanotubes (SWNT) covalently functionalized with aryl carboxylic acid or aryl hydroxyl groups in aqueous solution using UV−vis−nIR photoabsorption spectroscopy. Empirically, stable suspension is observed when the optical density at 632 nm is above 0.05. The critical level of functionalization required for surfactant-free aqueous suspension is found to be >1.5 and >5.1 functional groups per 100 carbons for the carboxylic acid and hydroxyl aryl groups, respectively. Solubility parameters are estimated by using established polymer solubility theory (Fedors and Refined Solubility Parameter group additivity models), molecular simulations (Maiti Dissipative Particle Dynamics), or a combination of both (Maiti-RSP and Maiti-Fedors). Flory−Huggins interaction parameters are calculated for suspensions of both chemistries in water and dimethyl formamide (DMF). Comparison of experiment and model indicates that the combined Maiti-RSP model best describes increasing solubility with increasing functionalization.

Study of higher excited states of some polyatomic molecules relevant for plasma physics and environment

Studies of higher excited states of some polyatomic molecules relevant for plasma physics and environment have been presented. Spectra of chlorofluorocarbons are discussed together with their influence on ozone layer depletion and global warming. Tetrahydrofuran molecule was studied by photoabsorption and electron energy loss spectroscopy while the states are assigned following extensive ab initio calculations. Nitrous oxide and hydrogen sulphide spectra are discussed in terms of identifying valence and Rydberg character of excited states.

Iodopentafluorobenzene: Electronic state spectroscopy by high-resolution vacuum ultraviolet photoabsorption and photoelectron spectroscopy

The electronic transitions of iodopentafluorobenzene (C 6F 5I) have been investigated experimentally for the first time by high-resolution photoabsorption spectroscopy in the energy range 3.6–10.7 eV. The character of the valence excited states has been discussed taking into account calculations available in the literature. The ionisation energies of the molecule in its electronic ground state have been measured by high-resolution He(I) photoelectron spectroscopy. The energies of the ionic bands are shifted by about 0.5 eV compared to the earliest literature values but they agree with the most recently published measurements. All the spectra presented in this paper represent highest resolution measurements of their kind for iodopentafluorobenzene. The absolute photoabsorption cross-sections have been used to model photolysis rates and residence times in the terrestrial atmosphere.

Photoabsorption resonances of Na20, Na21Cl and Na22Cl2 clusters

Plasma resonance profiles in the visible part of the spectrum were measured by photoabsorption spectroscopy for the clusters Na 20 , Na 21 Cl and Na 22 Cl 2 in a beam. The resonance positions in Na 20 and Na 21 Cl are close, suggesting that the Cl - ion does not locate at the center of the metallic droplet and does not strongly modify the effective valence electron density. The spectrum of Na 22 Cl 2 is noticeably dissimilar to the other two, raising the possibility of structural differences and/or incomplete charge transfer.

Valence shell electronic spectroscopy of isoprene studied by theoretical calculations and by electron scattering, photoelectron, and absolute photoabsorption measurements

The first ab initio calculations (vertical energies and oscillator strengths) are reported for the neutral electronic transitions of isoprene (2-methyl-1,3-butadiene), CH(2)CHC(CH(3))CH(2). The VUV photoabsorption spectroscopy of the molecule is presented in the energy range 4.6 to 10.8 eV (270-125 nm) with the highest resolution yet reported above 6.05 eV, revealing new spectral features. Valence and Rydberg transitions have been assigned in accordance with the theoretical results and the associated vibronic series have been analysed. The absolute photoabsorption cross sections at energies below 6.89 eV have been used to calculate the photolysis lifetime of isoprene in the upper stratosphere (20-50 km). Electron energy loss spectroscopy (EELS) measurements have enabled further photoabsorption cross sections to be derived in the range 9-28 eV. The first ab initio calculations have been carried out to determine excitation energies to the lowest energy ionic states of isoprene. The calculations are compared with the He(i) photoelectron spectrum (8 to 17 eV) and new vibrational structure is observed in the first photoelectron band.

Structure and predissociation of the 3pσuD Σ3u+ Rydberg state of N2: First extreme-ultraviolet and new near-infrared observations, with coupled-channels analysis

The 3psigma(u)D (3)Sigma(u) (+) Rydberg state of N(2) is studied experimentally using two high-resolution spectroscopic techniques. First, the forbidden D (3)Sigma(u) (+)-X (1)Sigma(g) (+) transition is observed for the first time via the (0,0) band of (14)N(2) and the (1,0) band of (15)N(2), using 1 extreme-ultraviolet +1 ultraviolet two-photon-ionization laser spectroscopy. Second, the Rydberg-Rydberg transition D (3)Sigma(u) (+)-E (3)Sigma(g) (+) is studied using near-infrared diode-laser photoabsorption spectroscopy, thus extending the previous measurements of Kanamori et al. [J. Chem. Phys. 95, 80 (1991)], to higher transition energies, and thereby revealing the (2,2) and (3,3) bands. The combined results show that the D(v=0-3) levels exhibit rapidly increasing rotational predissociation as v increases, spanning nearly four orders of magnitude. The D-state level structure and rotational predissociation signature are explained by means of a coupled-channels model which considers the electrostatically coupled (3)Pi(u) Rydberg-valence manifold, together with a pure-precession L-uncoupling rotational interaction between the 3psigma(u)D (3)Sigma(u) (+) and 3ppi(u)G (3)Pi(u) Rydberg p-complex components.

Optical observation of the C, 3sσgF3, and 3pπuG3 Π3u states of N2

High-resolution laser-based one extreme-ultraviolet (EUV)+one UV two-photon ionization spectroscopy and EUV photoabsorption spectroscopy have been employed to study spin-forbidden Π3u-X Σ1g+(v,0) transitions in N142 and N152. Levels of the C Π3u valence and 3sσgF3 and 3pπuG3 Π3u Rydberg states are characterized, either through their direct optical observation, or, indirectly, through their perturbative effects on the Π1u and Σ1u+ states, which are accessible in dipole-allowed transitions. Optical observation of the G3-X(0,0) and (1,0) transitions is reported for the first time, together with evidence for six new vibrational levels of the C state. Following the recent observation of the F3-X(0,0) transition at rotational resolution [J. P. Sprengers et al., J. Chem. Phys. 123, 144315 (2005)], the F3(v=1) level is found to be responsible for a local perturbation in the rotational predissociation pattern of the b′ Σ1u+(v=4) state. Despite their somewhat fragmentary nature, these new observations provide a valuable database on the Π3u states of N2 and their interactions which will help elucidate the predissociation mechanisms for the nitrogen molecule.

Neutral and charged excitations in carbon fullerenes from first-principles many-body theories

We investigate the accuracy of first-principles many-body theories at the nanoscale by comparing the low-energy excitations of the carbon fullerenes C(20), C(24), C(50), C(60), C(70), and C(80) with experiment. Properties are calculated via the GW-Bethe-Salpeter equation and diffusion quantum Monte Carlo methods. We critically compare these theories and assess their accuracy against available photoabsorption and photoelectron spectroscopy data. The first ionization potentials are consistently well reproduced and are similar for all the fullerenes and methods studied. The electron affinities and first triplet excitation energies show substantial method and geometry dependence. These results establish the validity of many-body theories as viable alternative to density-functional theory in describing electronic properties of confined carbon nanostructures. We find a correlation between energy gap and stability of fullerenes. We also find that the electron affinity of fullerenes is very high and size independent, which explains their tendency to form compounds with electron-donor cations.

Evolutions in time and space of laser ablated species by dual-laser photoabsorption spectroscopy

An atmospheric aluminum laser induced plasma is investigated by means of absorption and emission spectroscopies in the near ultraviolet range. The absorbed radiation is produced by a second aluminum laser induced plasma, which is generated at adjustable time delay. The measurements of both ground and resonant state number densities are derived from the fitting of the experimental 308.21 nm (P21/20−D23/2) and 396.15 nm (P23/20−S21/2) line absorption profiles on the numerical solution of the radiative transfer equation. Owing to the dominant role played by the Stark effect in the line broadening and shifting, the calculation also provides the evolution in time and in space of the free electron density along the line of sight. More classically, the same method is applied to the emission profiles which exhibit strong self-absorbed shapes. The reliability of the results derived from both absorption and emission experiments is analyzed and the origin of the asymmetric shape of the absorption lines is discussed.

Electronic states of neutral and ionized tetrahydrofuran studied by VUV spectroscopy and ab initio calculations

The electronic spectroscopy of isolated tetrahydrofuran (THF) in the gas phase has been investigated using high-resolution photoabsorption spectroscopy in the 5.8–10.6 eV with absolute cross-section measurements derived. In addition, an electron energy loss spectrum was recorded at 100 eV and 10° over the 5–11.4 eV range. The He(I) photoelectron spectrum was also collected to quantify ionisation energies in the 9–16.1 eV spectral region. These experiments are supported by the first high-level ab initio calculations performed on the excited states of the neutral molecule and on the ground state of the positive ion. The excellent agreement between the theoretical results and the measurements allows us to solve several discrepancies concerning the electronic state spectroscopy of THF. The present work reconsiders the question of the lowest energy conformers of the molecule and its population distribution at room temperature.

Electronic spectroscopy of bromopentafluorobenzene by high-resolution vacuum ultraviolet photoabsorption, electron impact, and photoelectron spectroscopies

The electronic transitions of bromopentafluorobenzene (C6F5Br) have been investigated by high-resolution photoabsorption spectroscopy in the energy range 4–10.8eV. In addition, the electron energy loss spectrum (EELS) was recorded in non-strictly electric dipolar interaction conditions (40eV incident energy, 10° scattering angle) over the range 4–13.0eV. The present spectra provide the first experimental data on the electronic states of bromopentafluorobenzene. The characteristics of the electronic excited states are discussed and the terrestrial atmospheric photolysis rates have been derived from the absolute photoabsorption cross-sections. The ionisation energies of the occupied molecular orbitals have been measured by high-resolution He(I) photoelectron spectroscopy, allowing a precise value of 9.679±0.002eV to be derived for the ionic ground state.

Hydrogen bonding in methanol clusters probed by inner-shell photoabsorption spectroscopy in the carbon and oxygen K-edge regions

Hydrogen bonding in methanol clusters has been investigated by using inner-shell photoabsorption spectroscopy and density functional theory (DFT) calculations in the carbon and oxygen K-edge regions. The partial-ion-yield (PIY) curves of H(CH(3)OH)(n)(+) were measured as the soft x-ray absorption spectra of methanol clusters. The first resonance peak in the PIY curves, which is assigned to the sigma*(O-H) resonance transition, exhibits a 1.20 eV blueshift relative to the total-ion-yield (TIY) curves of molecular methanol in the oxygen K-edge region, while it exhibits a shift of only 0.25 eV in the carbon K-edge region. Decreased intensities of the transitions to higher Rydberg orbitals were observed in the PIY curves of the clusters. The drastic change in the sigma*(O-H) resonance transition is interpreted by the change in the character of the sigma*(O-H) molecular orbital at the H-donating OH site due to the hydrogen-bonding interaction.

Electronic State Spectroscopy of c-C5F8 Explored by Photoabsorption, Electron Impact, Photoelectron Spectroscopies and Ab Initio Calculations

The electronic transitions and resonance-enhanced vibrational excitations of octafluorocyclopentene (c-C5F8) have been investigated using high-resolution photoabsorption spectroscopy in the energy range 6-11 eV. In addition, the high-resolution electron energy loss spectrum (HREELS) was recorded under the electric dipolar excitation conditions (100 eV incident energy, approximately 0 degrees scattering angle) over the 5-14 eV energy loss range. A He(I) photoelectron spectrum (PES) has also been recorded between 11 and 20 eV, allowing us to derive a more precise value of (11.288 +/- 0.002) eV for the ground neutral state adiabatic ionization energy. All spectra presented in this paper represent the first and highest resolution data yet reported for octafluorocyclopentene. Ab initio calculations have been performed for helping in the assignment of the spectral bands for both neutral excited states and ionic states.

The enhanced signal of subgap centers in tip-probing photoabsorption spectroscopy with an assist of a subsidiary light

We found that photoabsorption spectra (PASs) of a n-type Si exhibit a pronounced sub-bandgap peak when the sample was probed by a scanning tunneling microscope tip in a recently introduced scheme of Fourier transform (FT) spectroscopy. The peak, not observable in the conventional scheme of lock-in detection, emerged when, simulating the multiplex light illumination in the FT scheme, the sample was illuminated with a suprabandgap light in addition to the spectroscopic subgap lights. We concluded that this peculiar phenomenon is due to the optical neutralization of ionized donors by the subgap light which reduces, rather than increases, the surface photovoltage induced by the subsidiary suprabandgap lights. The use of such a subsidiary light in addition to spectroscopic lights will serve to enhance the sensitivity for tip-probing PAS detection of sub-bandgap centers.

Syntheses, structures and photophysical properties of iron containing hydroxyapatite prepared by a modified pseudo-body solution

It is known that bones and teeth are mostly composed of hydroxyapatite (HAp) and iron is present in them as a trace element. In order to search for helpful information for understanding the behavior of trace iron element in bones and teeth, very small amounts of iron containing HAp(FeHAp) were synthesized from a modified pseudo-body solution at low temperature. The effects of iron on the structural and photo-absorption properties of FeHAp were characterized by XRD, the Rietveld structural refinement, TEM and UV-vis photo-absorption spectroscopy. The results suggested that Fe(III) ions with high spin could get into the apatite structure and FeHAp with a pure apatitic phase could be obtained. At the same time, iron could modify the photo-absorption property of FeHAp. Compared with the pure HAp material, the prepared iron containing materials showed obviously photo-absorption property in the UV light region.

The VUV electronic spectroscopy of acetone studied by synchrotron radiation

The electronic state spectroscopy of acetone (CH3)2CO has been investigated using high-resolution VUV photoabsorption spectroscopy in the energy range 3.7-10.8 eV. New vibronic structure has been observed, notably in the low energy absorption band assigned to the 1(1)A(1) --> 1(1)A2 (ny --> pi*) transition. The local absorption maximum at 7.85 eV has been tentatively attributed to the 4(1)A1 (pi --> pi*) transition. Six Rydberg series converging to the lowest ionisation energy (9.708 eV) have been assigned as well as a newly-resolved ns Rydberg series converging to the first ionic excited state (12.590 eV). Rydberg orbitals of each series have been classified according to the magnitude of the quantum defect (delta) and are extended to higher quantum numbers than in the previous analyses.

Inner‐shell photoabsorption spectroscopy of push–pull nitroanilines—Theoretical and experimental studies at N 1s region

AbstractOscillator strengths for N 1s excitation spectra of the gas‐phase aniline and nitrobenzene, and the solid‐phase meta‐ and para‐nitroanilines have been derived from the total electron yield and total ion yield spectra acquired by tunable synchrotron radiation. Ab initio calculations carried out within the improved virtual orbital method and equivalent ionic core virtual orbital model have been used to aid spectral interpretation. The Rydberg‐valency mixture has also been evaluated for all compounds. These results are compared to those acquired with the extended hückel molecular orbital method [Goeta et al., Chem Mater, 2000, 12, 3342]. The building block model has been used to simulate the nitroanilines spectra. The sensitivity of core excitation spectroscopy to intramolecular nitroanilines charge transfer and the N 1s → π* spectral features dependence upon the substitution pattern (meta or para) have been confirmed, as already verified for the gas‐phase inner‐shell energy loss spectra for the same molecules [Turci et al., Can J Chem, 1996, 74, 851]. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008