LIF Spectroscopy Research Articles

Design and implementation of a new apparatus for astrochemistry: Kinetic measurements of the CH + OCS reaction and frequency comb spectroscopy in a cold uniform supersonic flow.

We present the development of a new astrochemical research tool, HILTRAC, the Highly Instrumented Low Temperature ReAction Chamber. The instrument is based on a pulsed form of the CRESU (Cinétique de Réaction en Écoulement Supersonique Uniforme, meaning reaction kinetics in a uniform supersonic flow) apparatus, with the aim of collecting kinetics and spectroscopic information on gas phase chemical reactions important in interstellar space or planetary atmospheres. We discuss the apparatus design and its flexibility, the implementation of pulsed laser photolysis followed by laser induced fluorescence, and the first implementation of direct infrared frequency comb spectroscopy (DFCS) coupled to the uniform supersonic flow. Achievable flow temperatures range from 32(3) to 111(9) K, characterizing a total of five Laval nozzles for use with N2 and Ar buffer gases by impact pressure measurements. These results were further validated using LIF and direct frequency comb spectroscopy measurements of the CH radical and OCS, respectively. Spectroscopic constants and linelists for OCS are reported for the 1001 band near 2890-2940cm-1 for both OC32S and OC34S, measured using DFCS. Additional peaks in the spectrum are tentatively assigned to the OCS-Ar complex. The first reaction rate coefficients for the CH + OCS reaction measured between 32(3) and 58(5) K are reported. The reaction rate coefficient at 32(3) K was measured to be 3.9(4) × 10-10cm3molecule-1s-1 and the reaction was found to exhibit no observable temperature dependence over this low temperature range.

Quantitative estimation of ·OH-radical density from fluorescence decay behavior near the plasma-liquid interface by incident microscopic LIF spectroscopy

The formation and transportation of short-lived species on/within the plasma-liquid interfacial layer plays a crucial role in various applications because of their high chemical reactivity. However, the experimental detection and quantification of these short-lived species, such as ˙OH radicals, at the gas–liquid interface still pose formidable challenges. This study confronts this challenge by employing incident microscopic laser-induced fluorescence (mLIF) method to capture the OH-LIF signals on the interfacial layer at different time moments of the post-discharge phase under high spatial resolution. The temporal evolution of ˙OH density is subsequently quantified by fitting the OH-LIF decay behavior to a reaction-dissolution model. Results reveal that increasing the pulse width serves better to enhance ˙OH generation on liquid surface, reaching a density of 1.25 × 1016 cm−3. Furthermore, the cathode-solution interface demonstrates significantly enhanced ˙OH production compared to the anode-solution interface. These results underscore the efficacy of incident mLIF in quantitatively probing short-lived ˙OH-radical production at the interfacial layer in pulsed-driven plasma-solution interactions, with potential applicability to other reactive species.

High-Power Laser Deposition of Chitosan Polymers: Medical and Environmental Applications.

High-power laser irradiation interaction with natural polymers in biocomposites and Laser-Induced Chitin Deacetylation (LICD) was studied in this work, in order to produce thin films consisting of chitosan composite. The new method can lead to a cutting-edge technology, as a response to the concern regarding the accumulation of “natural biological waste” and its use. The process consists of high-power laser irradiation applied on oyster shells as the target and deposition of the ablated material on different substrates. The obtained thin films we analyzed by FTIR, UV-VIS and LIF spectroscopy, as well as SEM-EDS and AFM. All the results indicated that chitin was extracted from the shell composite material and converted to chitosan by deacetylation. It was, thus, evidenced that chemical transformation in the chitin polymer side-chain occurs during laser irradiation of the oyster shell and in the resulted plasma plume of ablation. The numerical simulation in COMSOL performed for this study anticipates and confirms the experimental results of chitin deacetylation, also providing information about the conditions required for the physico-chemical processes involved. The high sorption properties of the thin films obtained by a LICD procedure is evidenced in the study. This quality suggests that they should be used in transdermal patch construction due to the known hemostatic and antibacterial effects of chitosan. The resulting composite materials, consisting of the chitosan thin films deposited on hemp fabric, are also suitable for micro-filters in water decontamination or in other filtering processes.

RF-CARS Combined with LIF Spectroscopy for Prediction and Assessment of Mine Water Inflow

RF-CARS Combined with LIF Spectroscopy for Prediction and Assessment of Mine Water Inflow

CEEMD: A New Method to Identify Mine Water Inrush Based on the Signal Processing and Laser-Induced Fluorescence

The rapid and accurate identification of water source types in mine water inrush has been achieved by combining laser-induced fluorescence technology (LIF) with artificial intelligence algorithms. However, these algorithms solely rely on data and image processing analysis to identify different kinds of water samples. To address this issue, we analyzed the fluorescence spectrum and the types of mine water inrush sources from the signal point of view. Firstly, a LIF water inrush spectral analysis system was built to collect spectral data and exhibit fluorescence spectra. Different methods of spectral signal decomposition and reconstruction were compared. The complementary ensemble empirical mode decomposition (CEEMD) algorithm with a better signal evaluation index was selected to preprocess raw spectral signals. Then, the multi-class support vector machine of the cuckoo search optimization (CS-MSVM) model was implemented to the reconstructed spectral signals in different stages. The classification accuracy of the reconstructed signals in the fifth stage was 100%. Compared with raw spectra, other signal processing methods, and other different classifiers, the proposed method has the highest classification accuracy. Finally, the reliability of the algorithm was validated by using the LIF spectral signals of different edible oils and the classification accuracy was 100%. The experimental results show that the CEEMD signal processing method combined with LIF spectroscopy is effective for the accurate identification of mine water inrush source, and it also provides a theoretical basis for the spectral analysis technology that can be used for the identification of other substances.

Consistent Franck–Condon modeling of geometry changes for the S0→S1(ππ*) excitation in anthranilic acid: LIF spectroscopy aided by CC2 or TDDFT vibrations

Experimentally-based evaluation of the changes of equilibrium geometry for the S0→S1(ππ*) excitation in anthranilic acid via fitting of Franck–Condon factors is tested for reliability. The modeling is based on the experimental band intensities in the LIF spectrum that are transformed into geometry changes with the aid of the vibrational modes computed using both the CC2 method (the perturbative approximation to CCSD coupled-cluster) and TDDFT(B3LYP). This modeling is a challenging task not only for quantitative spectroscopy, but also for the quantum chemistry calculations, since the adequate reproduction of vibrational modes for the excited state requires a balanced treatment of the π-electronic conjugation and dynamic electron correlation. The most reliable approach (LIF+CC2 Franck–Condon fitting) predicts a dramatic shortening of the O···H distance by 31 ± 1.5 pm, from 1.91 Å in the ground state to 1.60 Å in the excited state. The changes in bond alternation in the H-chelate ring (around 5 pm according to the LIF+CC2 fit) and the shortening of the O···H bond are typically 1 pm larger than modeled with the LIF+TDDFT fit. Changes of valence angles of magnitude around 5° are larger by 0.5°-1.0° according to LIF+CC2 FC fit than the LIF+DFT fit. Consistency of the obtained results shows that the Franck-Condon fitting provides a reliable, experimentally-based approach to evaluation of the excitation-related geometry changes. It has been achieved owing to the quantitatively reliable spectroscopic results and vibrational analysis computed using the quantum chemistry methods that are able to provide correct description of the excited-state vibrational modes involving the intramolecular hydrogen bond.

Observation and rotational analysis of the (0,0) [formula omitted]2Π − [formula omitted]2Σ+ transition in LaNH molecule and detection of [formula omitted]Δr state

The (0,0) band of the C∼2Πr − X̃2Σ+ system of LaNH was studied by LIF spectroscopy in a free-jet apparatus. The subbands, C∼2Π3/2 − X̃2Σ+ and C∼2Π1/2 − X̃2Σ+ were rotationally analyzed. Local perturbations were observed in f-parity levels of both spin components of the C∼ state which suggests presence of two 2Σ+/− perturber states. Dispersed fluorescence (DF) from the C∼2Π state suggests vibronic coupling in the C∼ state to a nearby 2Σ+ state. A low-lying Ã′2Δr electronic state was identified in the DF spectra with the Ω = 5/2 and 3/2 components lying respectively at 8353 and 7648 cm−1.

Experimental investigation of the hyperfine spectra of Pr I-lines: discovery of new fine structure energy levels of Pr I using LIF spectroscopy with medium angular momentum quantum number between 7/2 and 13/2

We present 39 even and 60 odd parity newly discovered fine structure levels of Pr I with angular momentum quantum numbers J = 7 / 2, 9/2, 11/2 and 13/2. Spectral lines in the wavelength range of 4200 A to 7500 A were investigated experimentally using laser-induced fluorescence spectroscopy or optogalvanic spectroscopy. Free Pr atoms were produced in a hollow cathode discharge. A high resolution Fourier transform spectrum of Pr was used to extract excitation wavelengths. From an analysis of the recorded hyperfine patterns, together with excitation and fluorescence wavelengths, we were able to find the unknown levels involved in the formation of the investigated lines. More than 500 spectral lines could be classified by the new levels.

LIF spectroscopy of NbN in free-jet: new bands in the 19,000–21,000 cm−1 region

ABSTRACTThe laser-induced fluorescence spectrum of NbN in the range 19,000–21,000 cm−1 has been studied in a free-jet apparatus. The rotationally resolved excitation spectrum has been recorded, dispersed fluorescence has been obtained and the radiative lifetimes of the upper electronic states have been measured. In addition to the previously reported sub-bands of 3Π–X3Δ transition, two new intense bands with R heads near 19,724.2 and 19,865.5 cm−1 have been observed and assigned as 0-0 bands of the 3Π1–X3Δ2 and –X3Δ1 sub-bands, respectively, of a new 3Π–X3Δ transition. These sub-bands position, respectively, 69 and 91 cm−1 to the blue side of the previously reported sub-bands. Seven more bands originating from the v″ = 1 level of the ground state were also identified and rotationally analysed.

Three new electronic transitions of CoS probed by LIF and DF spectroscopy

The laser-induced fluorescence excitation spectrum of jet-cooled CoS molecules has been recorded in the energy range of 20 100–22 600cm−1. Twenty-one bands have been assigned as three transition progressions: [21.58] 4Φ9/2(υ′=0–2) – A4Φ9/2(υ″=0–3), [21.65] 4Δ7/2(υ′=0–1) – A4Φ9/2(υ″=0–2), and [21.73] 4Φ9/2(υ′=0–2) – A4Φ9/2(υ″=0–4). Spectroscopic constants for the three newly identified electronically excited states and the A state have been determined for the first time. The dispersed fluorescence spectra related to most of these bands have been investigated, vibrationally excited levels of the ground and the A state have been observed. In addition, the lifetimes for almost all the observed bands have also been measured.

LIF spectroscopy of OH radicals in a micro-flow DC discharge in Ar and He with a liquid electrode

The laser-induced fluorescence spectroscopy on a micro-flow discharge with water electrode is carried out in order to investigate OH radicals. The branches P(2)(6), P(1)(4) and P(2)(3) of X(2) II, nu '' = 0-A(2) Sigma, nu' = 1 transition are used. Laser-induced fluorescence is used in order to estimate the density of OH radicals and density of water vapor in a core of the plasma. Sputtering yield of H(2)O from the liquid electrode is calculated based on experimental data. It is revealed that plasma core consists of 8-10% of water in both Ar and He discharges. The density of OH radicals in the micro-flow He plasma is higher than in the glow discharge with liquid electrode and in Ar micro-flow discharge due to constriction of the positive column and different mechanism of the OH radical production.

Pulsed laser photolysis vacuum UV laser-induced fluorescence kinetic study of the reactions of Cl( 2P 3/2) atoms with ethyl formate, n-propyl formate, and n-butyl formate

Cl( 2P 3/2) atoms were produced by photolysis of Cl 2 at 351 nm in the presence of alkyl formates and monitored by LIF spectroscopy at 134.72 nm. Rate coefficients of k(Cl + C 2H 5OC(O)H) = (9.5 ± 0.3)×10 −12, k(Cl + n-C 3H 7OC(O)H) = (4.5 ± 0.3) × 10 −11 and k(Cl + n-C 4H 9OC(O)H) = (1.2 ± 0.1) × 10 −10 cm 3 molecule −1 s −1 were determined at 295 ± 2 K in 6–7 Torr of Ar diluent. These values are 15–30% lower than reported in a previous pulsed laser photolysis resonance fluorescence study. The discrepancy may reflect complications arising from the fact that the time scales for chlorine atom loss and regeneration were not sufficiently decoupled in the previous study.

Plume investigations of the mechanisms of SiO laser ablation at 266 nm

The ablation mechanism of SiO at the laser wavelength of 266 nm has been investigated by characterizing the composition and dynamics of neutral and charged particles produced in the ablation. The neutral and ionized composition of the plume and the dynamics of neutral SiO were investigated by time-of-flight mass spectrometry. The velocity distribution of neutral SiO molecules shows contributions of slow and fast components. The velocity distributions of charged species in the plume were investigated by a Langmuir probe technique, obtaining that the distributions shift towards higher velocities with increasing distance from the target surface. The fastest component of the velocity distribution of neutral SiO overlaps the slowest part of the velocity distribution of charged species. The average rotational energy of SiO molecules, estimated by LIF spectroscopy does not allow to draw clear conclusions about the participation of silicon oxide ion clusters as the precursors of fast SiO molecules in the plume.

Pulsed Laser Photolysis Vacuum UV Laser-Induced Fluorescence Kinetic Study of the Gas-Phase Reactions of Cl(2P3/2) Atoms with C3−C6 Ketones

The gas-phase reactions of Cl atoms with acetone, butanone, 2-pentanone, 3-pentanone, 2-hexanone, 3-hexanone, and cyclopentanone at 295 +/- 2 K were studied using pulsed laser photolysis vacuum UV laser-induced fluorescence (PLP-LIF) techniques. Cl(2P(3/2)) atoms were produced by photolysis of Cl2 at 351 nm and monitored by LIF spectroscopy at 134.72 nm (3p(5) 2P(3/2)-3p(4)4s 2P(3/2) transition). Rate coefficients for reactions of Cl atoms with acetone, butanone, 2-pentanone, 3-pentanone, 2-hexanone, 3-hexanone, and cyclopentanone are (2.30 +/- 0.12) x 10(-12), (4.08 +/- 0.21) x 10(-11), (1.23 +/- 0.13) x 10(-10), (8.87 +/- 0.92) x 10(-11), (2.08 +/- 0.32) x 10(-10), (1.43 +/- 0.19) x 10(-10) and (1.16 +/- 0.12) x 10(-10) cm3 molecule(-1) s(-1), respectively. The results for acetone and butanone are consistent with previous studies. The results for 2-pentanone, 3-pentanone, 2-hexanone, and 3-hexanone are approximately a factor of 2-3 higher than those from previous absolute rate studies. Likely explanations for these discrepancies are discussed. Tropospheric lifetimes of ketones with respect to reaction with Cl atoms are estimated and discussed.

MEKC: An update focusing on practical aspects

This paper reviews recent methodological and instrumental advances in MEKC. Improvements in sensitivity arising from the use of on-line sample concentration (sweeping, stacking, and combination of both protocols) and derivatization (in-capillary reactions and coupling with flow-injection systems) and improvements in resolution obtained by changing the composition of the BGE (e.g., with organic modifiers, ionic liquids, nonionic and zwitterionic surfactants, mixed micelles, and vesicles) or using coated capillaries are discussed in detail. In addition, MS and LIF spectroscopy are examined in relation to their advantages and restrictions as applied to MEKC analysis. Some thoughts on potential future directions are also expressed.

Image analysis and laser induced fluorescence combined to determine biological growth on silicone rubber insulators

High-voltage outdoor insulators made from silicone rubber are sometimes reported to be colonised by microorganisms. When the hydrophobic polymeric surface is covered by a hydrophilic biofilm, the electrical properties of the insulator are altered. In this work, mixed biofilms, similar to those formed on the surfaces of polymeric insulators in the field, were successfully grown on five types of silicone rubber substrates in the laboratory, using specially designed microenvironment chambers. Photography and digital image analysis were utilized to estimate the areas covered by the growth. It was found that direct UV-light exposure hindered growth of the biofilms. Further, growth was also hindered on samples where zinc borate had been added as flame retardant. In contrast, addition of ATH did not influence the growth. In parallel, LIF spectroscopy was explored as a tool for detection of biofilms on silicon rubber samples. Experiments revealed that even weak traces of growth, not visible to the naked eye, could be detected. Finally, it is believed that LIF spectroscopy in combination with image analysis can be used for field diagnostics of biological growth on insulators in service.

Inelastic state-to-state scattering of OH (Π3∕22,J=3∕2,f) by HCl

Parity resolved state-to-state cross sections for inelastic scattering of OH (X2Pi) by HCl were measured in a crossed molecular beam experiment at the collision energy of 920 cm(-1). The OH (X2Pi) radicals were prepared in a single quantum state, Omega=3/2, J=3/2, MJ=3/2, f, by means of electrostatic state selection in a hexapole field. The rotational distribution of the scattered OH radicals by HCl was probed by saturated LIF spectroscopy of the 0-0 band of the A 2Sigma+ - X 2Pi transition. Relative state-to-state cross sections were measured for rotational excitations up to J=9/2 within the Omega=3/2 spin-orbit manifold and up to J=7/2 within the Omega=1/2 spin-orbit manifold. A propensity for spin-orbit conserving transitions was found, but no propensity for excitation into a particular Lambda-doublet component of the same rotational state was evident. The data are presented and discussed in comparison with results previously obtained for collisions of OH with CO (Ecoll=450 cm(-1)) and N2 (Ecoll=410 cm(-1)) and with new data we have measured for the OH+CO system at a comparable collision energy (Ecoll=985 cm(-1)). This comparison suggests that the potential energy surface (PES) governing the interaction between OH and HCl is more anisotropic than the PES's governing the intermolecular interaction of OH with CO and N2.

Bio-compatibility of ion beam-modified and RGD-grafted polyethylene

Polyethylene (PE) was implanted with 15 keV Ar + and Kr + ions to the fluences from 3 × 10 12–1 × 10 15 cm −2 and subsequently grafted with amino acid sequence Arg–Gly–Asp (RGD), i.e. a minimum adhesion motif recognized by integrin receptors on cells. The structural changes of PE were studied using goniometric technique, UV–VIS, LIF spectroscopy and by measuring specimen electrical resistance. The adhesion and proliferation of mouse embryonic fibroblasts 3T3 on the modified PE were studied under in vitro conditions. Addition of RGD sequence onto double bonds created by the ion irradiation on polymeric chain was observed. The adhesion and proliferation of the 3T3 cells is increased by ion implantation and additionally also by RGD grafting.

Predissociation of Excited Acetylene in the ÃAu State around the Adiabatic Dissociation Threshold as Studied by LIF and H-Atom Action Spectroscopy

The LIF and H-atom action spectra of the A−X transition of acetylene in a supersonic jet were observed in the excitation-energy range of 47 000−50 600 cm-1, where 60 vibrational states were identified in the A state through rotational analyses of respective bands. Most of these states originate from anharmonic couplings of the Franck−Condon-allowed 2m3n states with the 4i6j states where i + j = even. This fact is consistent with the determined rotational constants of respective states whose values are mostly between those of the 2m3n(m ≤ 1, n ≤ 4) and the 41 or 61 state. The line intensities of the H-atom action spectra increase at the higher excitation energies, indicating more efficient predissociation. The lifetimes of respective excited states were evaluated from the observed spectral line widths. In a higher excitation-energy region, the lifetime is shortened from 100 ps at 47 000 cm-1 to 25 ps at 50 600 cm-1, which exceeds the adiabatic dissociation threshold of the A state by 933 cm-1 and is the w...

IR laser-induced thermolysis of (chloromethyl)silane: complex reaction involving H2Si:, H2C: and HClSi: transients and yielding nanostructured Si/C/H phases

Multi-pulse and single-pulse infrared laser induced thermolysis of gaseous (chloromethyl)silane, H3SiCH2Cl occurs via 1,1-HCl and H2C: elimination and dehydrogenation and yields nano-structured Si/C/H phases containing most of the Si and C atoms of the precursor. The identification of final volatile products and observation of H2Si:, H2C: and HClSi: transients by LIF spectroscopy suggest that intermediate silene isomers decompose into silylene and carbene. The deposited films are composed of SiC and polycarbosilane and their H content differs depending on the mode of the IR thermolysis.