Laser-induced Fluorescence Studies Research Articles

Evidence for the Specific Species of Benzyltriethoxysilane Derivatives with a High-Coordination Silicon Atom

Evidence for the specific species of benzyltriethoxysilane derivatives with a high-coordination silicon atom is presented. Nanosecond laser flash photolyses of benzyltriethoxysilane and triethoxysilyldiphenylmethane have been studied in polar and nonpolar solvents. For the transient absorption spectra of benzyltriethoxysilane and triethoxysilyldiphenylmethane in methanol, a characteristic band attributed to the benzyl radical or diphenylmethyl radical was observed at around 317 and 330 nm, with a second-order decay rate constant of 5.7 × 10(9) and 4.2 × 10(9) M(-1) s(-1), respectively. While in cyclohexane, an absorption band attributable to the specific species with a high-coordination silicon atom was observed at around 330 nm with a first-order decay rate constant of 5.7 × 10(4) and 1.2 × 10(4) s(-1) for benzyltriethoxysilane and triethoxysilyldiphenylmethane, respectively. A two-step laser-induced fluorescence study of triethoxysilyldiphenylmethane supports the assignment that the transient absorption bands observed at around 330 nm in methanol and in cyclohexane are ascribed to the diphenylmethyl radical and the specific species of triethoxysilyldiphenylmethane with a high-coordination silicon atom, respectively. The candidates for this specific species with a high-coordination silicon atom have been calculated by means of the TD-DFT method and SAC-CI method, and their molecular structures were discussed.

Laser-induced fluorescence study of medieval frescoes by Giusto de’ Menabuoi

Abstract Laser-induced fluorescence (LIF) is a powerful remote and non-invasive analysis technique that has been successfully applied to the real-time diagnosis of historical artworks. Hyperspectral images collection on fresco's and their false colours processing allowed to reveal features invisible to the naked eye and to obtain specific information on pigments composition and consolidants utilization, the latter also related to former restorations. This report presents the results obtained by ENEA LIF scanning system during a field campaign conducted in June 2010 on fresco's by Giusto de’ Menabuoi in the Padua Baptistery. The data collected by LidArt allowed the detection of Paraloid B72 and Movilith/Primal AC33, guiding the restorers in their conservation actions.

Laser-induced fluorescence study of spin–orbit quenching of Cl(2P1/2) by H2, D2, and HD gases

Employing ultraviolet laser flash photolysis in combination with pulsed vacuum ultraviolet laser induced-fluorescence spectroscopy room-temperature rate constants kQ,H2=(5.8±0.6)×10−11cm3s−1, kQ,D2=(5.6±0.6)×10−12cm3s−1, and kQ,HD=(2.7±0.3)×10−11cm3s−1 for electronically non-adiabatic quenching of spin–orbit excited Cl(2P1/2) atoms in collisions with H2, D2, and HD gases were determined, which allow for comparison with results of recent quantum-scattering calculations [14,15].

Insights on the CN B 2Σ+ + Ar potential from ultraviolet fluorescence excitation and infrared depletion studies of the CN–Ar complex

UV laser-induced fluorescence and IR-UV fluorescence depletion studies have been used to characterize the intermolecular levels of the CN-Ar complex in the excited state correlating with CN B (2)Σ(+) + Ar. Additional CN-Ar features are identified to lower wavenumber than reported previously. Fluorescence depletion spectra are recorded to confirm that these CN-Ar features and other higher energy features in the B-X spectrum originate from a common ground state level. The UV depletion is induced by IR excitation of CN-Ar from the ground state zero-point level to a hindered internal rotor state (n(K) = 1(1)) in the CN overtone region. The lowest energy feature in the B-X spectrum at 25,714.1 cm(-1) is assigned as a transition to the zero-point level of the B state and also yields its binding energy, D(0) = 186(2) cm(-1), which is in excellent accord with theoretical predictions. The next feature approximately 40 cm(-1) higher is attributed to overlapping transitions to intermolecular levels with bend (v(b)(K)=1(1)) or stretch (v(s) = 1) excitation. Yet higher features (previously reported) are also assigned, based on their transition type and wavenumber, which are consistent with the intermolecular energy level pattern computed theoretically. Finally, the intensity profile of the lowest energy features in the B-X spectrum reflects the predicted change in the CN (B (2)Σ(+), X (2)Σ(+)) + Ar potentials upon electronic excitation from a weakly anisotropic potential about the linear N≡C-Ar configuration in the ground state to a more strongly bound linear C≡N-Ar structure in the excited B electronic state.

A laser-induced fluorescence study of the jet-cooled nitrous oxide cation (N2O+)

Laser-induced fluorescence and wavelength resolved emission spectra of the à (2)Σ(+) - X̃ (2)Π(i) electronic transition of the jet-cooled nitrous oxide cation have been recorded. The ions were produced in a pulsed electric discharge at the exit of a supersonic expansion using a precursor mixture of N(2)O in high pressure argon. Both spin-orbit components of the 0(0) (0) band were studied at high resolution and rotationally analyzed to provide precise molecular constants for the combining states. Emission spectra were obtained by laser excitation of the 0(0) (0), 2(0) (1), 3(0) (1), and 2(0) (2) absorption bands, providing extensive data on the ground state bending, stretching, and combination vibrational levels. These data were fitted to a Renner-Teller model including spin-orbit, anharmonic, and Fermi resonance terms. The observed energy levels and fitted parameters were found to be comparable to those in the literature predicted from an ab initio potential energy surface.

Laser induced fluorescence study on the growth of maize plants

The laser induced fluorescence (LIF) spectra from plants give accurate information on the influences of ultraviolet A (UV-A) and ultraviolet B (UV-B) radiation on the growth of maize plants. In this paper, a thorough LIF study has been done on maize plants grown under controlled conditions. The maize (Zea mays) seeds were planted and exposed to UV-A and UV-B radiation from 0 to10 hours. The decrease in the ratios of peaks of LIF confirm a decrease in the height, diameter of stem, number of leaves in the plants exposed to UV-B and UV-A with the increase in the time of exposure.

Complexation of novel diglycolamide functionalized calix[4]arenes: Unusual extraction behaviour, transport, and fluorescence studies

Three diglycolamide functionalized calix[4]arenes (calix[4]-nDGA) were synthesized and evaluated for their extraction behaviour towards lanthanide/actinide ions. Exceptionally high D(Am) and D(Pu) values indicate these radiotoxic elements can be selectively removed from nuclear waste solutions. Transport and laser induced fluorescence studies indicated strong complexation of the trivalent metal ions with the calix[4]-4DGA ligand.

Laser-induced fluorescence studies of HfF+ produced by autoionization

Autoionization of Rydberg states of HfF, prepared using the optical-optical double resonance technique, holds promise to create HfF(+) in a particular Zeeman level of a rovibronic state for an electron electric dipole moment search. We characterize a vibronic band of Rydberg HfF at 54 cm(-1) above the lowest ionization threshold and directly probe the state of the ions formed from this vibronic band by performing laser-induced fluorescence on the ions. The Rydberg HfF molecules show a propensity to decay into only a few ion rotational states of a given parity and are found to preserve their orientation qualitatively upon autoionization. We show empirically that we can create 30% of the total ion yield in a particular ∣J(+), M(+)<linear span> state and present a simplified model describing autoionization from a given Rydberg state that assumes no angular dynamics.

Trends in Ln(III) Sorption to Quartz Assessed by Molecular Dynamics Simulations and Laser-Induced Fluorescence Studies

Molecular dynamics simulations were performed to examine trends in trivalent lanthanide [Ln(III)] sorption to ≡SiOH0 and ≡SiO– sites on the 001 surface of α-quartz across the 4f period. Complementary laser-induced fluorescence studies examined Eu(III) sorption to α-quartz at a series of ionic strengths from 1 × 10–4 M to 0.5 M such that properties of the surface-sorbed species could be extrapolated to zero ionic strength, the conditions under which the simulations are performed. Such extrapolation allows for a more direct comparison of the data and enables a molecular understanding of the surface-sorbed species and the role of the ion surface charge density upon the interfacial reactivity. Potential of mean force molecular dynamics as well as simulations of presorbed Ln(III) species agrees with the spectroscopic study of Eu(III) sorption, indicating that strongly bound inner-sphere complexes are formed upon sorption to an ≡SiO– site. The coordination shell of the ion contains 6–7 waters of hydration, and it is predicted that surface silanol OH groups transfer from the quartz to the inner coordination shell of Eu(III). Molecular simulations predict less-strongly bound inner-sphere species in early lanthanides and more strongly bound species in late lanthanides, following trends in the surface charge density of the 4f ions. Hydroxyl ligands that derive from the surface silanol groups are consistently observed to bind in the inner coordination shell of surface-sorbed inner-sphere Ln(III) ions, provided that the ion is able to migrate within 2.0–3.0 Å of the plane formed by the silanol O atoms (∼3.5 Å from an individual ≡SiO– group). Sorption to a fully protonated quartz surface is not predicted to be favorable by any Ln(III), except perhaps Lu. The present work demonstrates a combined theoretical and experimental approach in the prediction of the fate of trivalent radioactive contaminants at temporary and permanent nuclear waste storage sites.

The nascent OH detection in photodissociation of 2-(bromomethyl)hexafluoro-2-propanol at 193 nm: Laser-induced fluorescence study

Photodissociation of 2-(bromomethyl)hexafluoro-2-propanol (BMHFP) and 3-bromo-1-propanol (BP), involving σ C – Br * ← n Br transition at 193 nm, has been investigated by measuring laser-induced fluorescence spectra of the expected OH product. The OH channel is a minor dissociation pathway with a quantum yield of 0.17 ± 0.05 in BMHFP, whereas it was not observed in BP. Partitioning of the available energy into translation, rotation, and vibration of the photoproducts has been measured by state selective detection of the nascent OH product in BMHFP. OH is produced mostly in the ground vibrational level ( v″ = 0), with a rotational distribution being characterized by a temperature of 465 ± 25 K. But, a significant fraction of the available energy of 30.2 kcal mol −1 is partitioned into translation of OH (14.6 kcal mol −1). The OH( v″ = 0, J″) populations in the spin-orbit states as well as in the Λ-doublet states are statistical. A plausible mechanism of OH formation on excitation of BMHFP at 193 nm is suggested, with the primary reaction channel being elimination of Br atom by direct C–Br bond dissociation from a repulsive surface. The Br radical is detected using (2 + 1) resonance-enhanced multiphoton ionization (REMPI) at ∼234 nm. It is produced in both the ground ( 2P 3/2) and the excited ( 2P 1/2) spin-orbit states with the relative quantum yield of the latter to be 0.36. The co-fragment of Br undergoes secondary C–O bond dissociation to produce OH and F 3C–C( CH 2)–CF 3, with the reaction having a barrier located in the exit channel. In this two-step three-body dissociation process, a major fraction of the available energy is released into translation (〈 f T〉 ∼ 0.75), resulting from an impulsive C–Br bond dissociation in the primary step and presence of an exit barrier in the secondary process. Experimental results combined with theoretical calculations provide a clear picture of the dynamics of OH formation from BMHFP at 193 nm. In addition, the energetics of another channel, competing with OH, have been calculated from the primary product F 3C–C(CH 2)(OH)–CF 3. In contrast to BMHFP, the OH product could not be observed from the photolysis of 3-bromo-1-propanol (another saturated halogenated propanol) at 193 nm under the detection limit of the present experimental condition, although it has a higher absorption cross-section at 193 nm.

Comprehensive Studies on an Overall Proton Transfer Cycle of the ortho-Green Fluorescent Protein Chromophore

Initiated by excited-state intramolecular proton transfer (ESIPT) reaction, an overall reaction cycle of 4-(2-hydroxybenzylidene)-1,2-dimethyl-1H-imidazol-5(4H)-one (o-HBDI), an analogue of the core chromophore of the green fluorescent protein (GFP), has been investigated. In contrast to the native GFP core, 4-(4-hydroxybenzylidene)-1,2-dimethyl-1H-imidazol-5(4H)-one (p-HBDI), which requires hydrogen-bonding relay to accomplish proton transfer in vivo, o-HBDI possesses a seven-membered-ring intramolecular hydrogen bond and thus provides an ideal system for mimicking an intrinsic proton-transfer reaction. Upon excitation, ESIPT takes place in o-HBDI, resulting in a ∼600 nm proton-transfer tautomer emission. The o-HBDI tautomer emission, resolved by fluorescence upconversion, is comprised of an instantaneous rise to a few hundred femtosecond oscillation in the early relaxation stage. Frequency analysis derived from ultrashort pulse gives two low-frequency vibrations at 115 and 236 cm(-1), corresponding to skeletal deformation motions associated with the hydrogen bond. The results further conclude that ESIPT in o-HBDI is essentially triggered by low-frequency motions and may be barrierless along the reaction coordinate. Femtosecond UV/vis transient absorption spectra also provide supplementary evidence for the structural evolution during the reaction. In CH(3)CN, an instant rise of a 530 nm transient is resolved, which then undergoes 7.8 ps decay, accompanied by the growth of a rather long-lived 580 nm transient species. It is thus concluded that following ESIPT the cis-proton transfer isomer undergoes cis-trans-isomerization. The results of viscosity-dependent dynamics are in favor of the one-bond-flip mechanism, which is in contrast to the volume-conserving isomerization behavior for cis-stilbene and p-HBDI. Further confirmation is given by the picosecond-femtosecond transient IR absorption spectra, where several new and long-lived IR bands in the range of 1400-1500 cm(-1) are assigned to the phenyl in-plane breathing motions of the trans-proton transfer tautomer. Monitored by the nanosecond transient absorption, the 580 nm transient undergoes a ∼7.7 μs decay constant, accompanied by the growth of a new ∼500 nm band. The latter is assigned to a deprotonated tautomer species, which then undergoes the ground-state reverse proton recombination to the original o-HBDI in ∼50 μs, achieving an overall, reversible proton transfer cycle. This assignment is unambiguously supported by pump-probe laser induced fluorescence studies. On these standpoints, a comparison of photophysical properties among o-HBDI, p-HBDI, and wild-type GFP is discussed in detail.

Theoretical study of Al+–RG (RG=He–Rn)

We present the results of CCSD(T) calculations on the full set of Al(+)-RG complexes (RG = He-Rn). Potential energy curves are calculated pointwise, employing the full counterpoise correction and basis sets of quadruple-ζ and quintuple-ζ quality, and then extrapolated to the complete basis set limit. Each curve has been employed to calculate rovibrational energy levels, from which spectroscopic parameters have been derived. These are compared to the available experimental data, and it is seen that there is excellent agreement with the values obtained from both Rydberg state extrapolations and high-resolution laser-induced fluorescence studies. Finally, we have also used our potentials to calculate transport coefficients for Al(+) moving through a bath of RG.

ChemInform Abstract: Transient Absorption and Two-Step Laser-Induced Fluorescence Studies of the Intramolecular Excited-State Proton Transfer and Relaxation Process in 2-Naphthyl-3-hydroxychromones.

ChemInform Abstract: Transient Absorption and Two-Step Laser-Induced Fluorescence Studies of the Intramolecular Excited-State Proton Transfer and Relaxation Process in 2-Naphthyl-3-hydroxychromones.

B-X and C-X Band Systems of CuCl Revisited: Laser-induced Fluorescence Study in 465–490 nm

We have reinvestigated the B-X and C-X band systems of CuCl by recording the laser-induced fluorescence excitation spectra in 20400–21800 cm−1. The rotational analyses in Hund's case (a) revealed unambiguously a singlet-to-singlet transition nature. The radiative lifetimes were measured to be 4.670 and 4.667 μs, respectively, which are much longer than that expected for a pure singlet of CuCl. This implies that the fluorescence mechanism in the B or C band systems lies in the mixing of the singlets (1Π and 1σ+) and triplets (3Π0,1,2) and that the two excited states observed in our experiment might be the singlets that have been strongly “contaminated" by their triplet neighbors.

Laser-induced fluorescence and dispersed fluorescence studies of the donor–acceptor system 4-amino 3-methyl benzoic acid methyl ester and its solvated clusters: Evidence of excited-state charge-transfer reaction

Laser-induced fluorescence (LIF) excitation and dispersed fluorescence (DF) spectra of 4-amino 3-methyl benzoic acid methyl ester (AMBME) and its solvated clusters with solvents such as methanol, water and acetonitrile have been investigated in a supersonic expansion. Spectral signature supports the presence of two conformers in the cooled jet which is in line with theoretical calculations. In addition to structured local emission from the Franck Condon excited state, the molecule AMBME shows red-shifted broad emission from the state attributed to the close-lying charge transfer (CT) state, which is facilitated by exciting low-frequency modes. The molecule readily forms clusters with different solvents and the clusters’ electronic excitation bands appear in the low-energy side of the transition origin of the bare molecule. Excitation of the clusters leads to the appearance of red-shifted solvent-polarity dependent CT emission.

Does Maternal Treatment with Zidovudine Affect Changes in Mandibles of Newborns? Laser Induced Fluorescence Study

The influence of antiretroviral drug zidovudine treatment during pregnancy on mandible development in newborn rats was studied. The fluorescence of mandibles from 7-, 14- and 28-days old individuals was measured by means of fiber-optical fluorescence analyzer with 407 nm laser excitation. Obtained results revealed disturbing effect of maternal zidovudine administration on mandible fluorescence intensity which should decrease with bone development. Small changes in fluorescence of porphyrin forms are maintaining in the first month of newborns life while the changes observed in 440-585 nm range disappear.

A laser induced fluorescence study relating to physical properties of the iodine monoxide radical

The dispersed fluorescence spectra originating from the v' = 2 and v' = 0 levels of the A(2)Pi(3/2) state of iodine monoxide (IO) have been recorded for the first time after laser induced fluorescence (LIF) excitation in the A(2)Pi(3/2)<-- X(2)Pi(3/2) electronic transition. The results are used to obtain relative Franck-Condon factors for various v'-->v'' transitions in the A(2)Pi(3/2)--> X(2)Pi(3/2) system up to v'' = 12 and compared with theoretical predictions. A fluorescence quenching study of the A(2)Pi(3/2) state of IO has also been performed, revealing that collisional quenching and rotational energy transfer (RET) are rapid in the A(2)Pi(3/2) state of IO. The J'-dependence to fluorescence quenching of the A(2)Pi(3/2) (v' = 2) state of IO by N(2) suggests a collisional predissociation mechanism.

Direct Observation of the Gas Phase Reaction of the Cyclohexyl Radical with Dioxygen Using a Distonic Radical Ion Approach

Alkylperoxyl radicals are intermediates in the oxidation of hydrocarbons. The reactive nature of these intermediates, however, has made them elusive to direct observation and isolation. We have employed ion trap mass spectrometry to synthesize and characterize 4-carboxylatocyclohexyl radical anions (*C(6)H(10)-CO(2)(-)) and observe their reactivity in the presence of dioxygen. The resulting reaction is facile (k = 1.8 x 10(-10) cm(3) molecule(-1) s(-1) or 30% of calculated collision rate) and results in (i) the addition of O(2) to form stabilized 4-carboxylatocyclohexylperoxyl radical anions (*OO-C(6)H(10)-CO(2)(-)), providing the first direct observation of a cyclohexylperoxyl radical, and (ii) elimination of HO(2)* and HO* radicals consistent with recent laser-induced fluorescence studies of the reaction of neutral cyclohexyl radicals with O(2). Electronic structure calculations at the B3LYP/6-31+G(d) level of theory reveal viable pathways for the observed reactions showing that formation of the peroxyl radical is exothermic by 37 kcal mol(-1) with subsequent transition states as low as -6.6 kcal mol(-1) (formation of HO(2)*) and -9.1 kcal mol(-1) (formation of HO*) with respect to the entrance channel. The combined computational and experimental data suggest that the structures of the reaction products correspond to cyclohexenes and epoxides from HO(2)* and HO* loss, respectively, while alternative pathways leading to cyclohexanone or ring-opened isomers are not observed. Activation of the charged peroxyl radical *OO-C(6)H(10)-CO(2)(-) by collision induced dissociation also results in the loss of HO(2)* and HO* radicals confirming that these products are directly connected to the peroxyl radical intermediate.

Terahertz-Radiation-Enhanced Emission of Fluorescence from Gas Plasma

We report the study of femtosecond laser-induced air plasma fluorescence under the illumination of terahertz (THz) pulses. Semiclassical modeling and experimental verification indicate that time-resolved THz radiation-enhanced emission of fluorescence is dominated by the electron kinetics and the electron-impact excitation of gas molecules or ions. We demonstrate that the temporal waveform of the THz field could be retrieved from the transient enhanced fluorescence, making omnidirectional, coherent detection available for THz time-domain spectroscopy.

A time-resolved laser induced fluorescence study on the ion velocity distribution function in a Hall thruster after a fast current disruption

The temporal characteristics of the Xe+ ion axial velocity distribution function (VDF) were recorded in the course of low-frequency discharge current oscillations (∼14 kHz) of the 5 kW class PPS®X000 Hall thruster. The evolution in time of the ion axial velocity component is monitored by means of a laser induced fluorescence diagnostic tool with a time resolution of 100 ns. As the number of fluorescence photons is very low during such a short time period, a homemade pulse-counting lock-in system was used to perform real-time discrimination between background photons and fluorescence photons. The evolution in time of the ion VDF was observed at three locations along the thruster channel axis after a fast shutdown of the thruster power. The anode discharge current is switched off at 2 kHz during 5 μs without any synchronization with the current oscillation cycle. This approach allows to examine the temporal behavior of the ion VDF during decay and ignition of the discharge as well as during forced and natural plasma oscillations. Measurements show that the distribution function of the axial component of the Xe+ ion does change periodically in time with a frequency close to the current oscillation frequency in both forced and natural cases. The ion density and the mean velocity are found to oscillate, whereas the velocity dispersion stays constant, which indicates that ionization and acceleration layers have identical dynamics. Finally, variations over time in the electric field are for the first time experimentally evidenced in a crossed-field discharge.