High-resolution Laser-induced Fluorescence Research Articles

Extending the Large Molecule Limit: The Role of Fermi Resonance in Developing a Quantum Functional Group.

Polyatomic molecules equipped with optical cycling centers (OCCs), enabling continuous photon scattering during optical excitation, are exciting candidates for advancing quantum information science. However, as these molecules grow in size and complexity, the interplay of complex vibronic couplings on optical cycling becomes a critical but relatively unexplored consideration. Here, we present an extensive exploration of Fermi resonances in large-scale OCC-containing molecules using high-resolution dispersed laser-induced fluorescence and excitation spectroscopy. These resonances manifest as vibrational coupling leading to intensity borrowing by combination bands near optically active harmonic bands, which require additional repumping lasers for effective optical cycling. To mitigate these effects, we explore altering the vibrational energy level spacing through substitutions on the phenyl ring or changes in the OCC itself. While the complete elimination of vibrational coupling in complex molecules remains challenging, our findings highlight significant mitigation possibilities, opening new avenues for optimizing optical cycling in large polyatomic molecules.

High-resolution laser spectroscopy of the [formula omitted][formula omitted] transition in YbOD

Ytterbium monohydroxide (YbOH) and its isotopologues are good candidate molecules for use in the search for physics beyond the standard model. We present a rotational analysis of the Ã2Π1/2−X̃2Σ+ transition in 174YbOD, the deuterated analogue of 174YbOH, based on high-resolution laser-induced fluorescence spectra. The band origin T0= 17993.81014(33) cm−1 was shifted to the red of the 174YbOH origin (T0= 17998.5875(2) cm−1). The ground state rotational parameter is B = 0.2205648(72) cm−1, which compares favourably to the value of 0.2203 cm−1 estimated by isotopically scaling the 174YbOH value of B = 0.245116257(1) cm−1.

Regional Models for Sentinel-2/MSI Imagery of Chlorophyll a and TSS, Obtained for Oligotrophic Issyk-Kul Lake Using High-Resolution LIF LiDAR Data

The development of regional satellite bio-optical models for natural waters with high temporal and spatial variability, such as inland seas, reservoirs, and coastal ocean waters, requires the implementation of an intermediate measuring link in the chain, “water sampling—bio-optical models”, and this link must have certain intermediate characteristics. The most crucial of them are the high-precision measurements of the main water quality parameters, such as the concentration of chlorophyll a (Chl a), colored dissolved organic matter (CDOM), and total suspended sediments (TSS) in the upper water layer, together with a high operational rate and the ability to cover a large water area in a short time, which corresponds to a satellite overpass. A possible solution is to utilize laser-induced fluorescence (LIF) of water constituents measured by a marine LiDAR in situ with a high sampling rate from a high-speed vessel. This allows obtaining a large ground-truth dataset of the main water quality parameters simultaneously with the satellite overpass within the time interval determined by NASA protocols. This method was successfully applied to the oligotrophic Issyk-Kul Lake in Kyrgyzstan, where we obtained more than 4000 and 1000 matchups for the Chl a and TSS, respectively. New preliminary regional bio-optical models were developed on the basis of a one-day survey and tested for archive Sentinel-2A data for 2022. This approach can be applied for regular monitoring and further correction in accordance with seasonal variability. The obtained results, together with previously published similar studies for eutrophic coastal and productive inland waters, emphasize the applicability of the presented method for the development or adjustment of regional bio-optical models for water bodies of a wide trophic range.

Quantitative laser diagnostics on trimethylindium pyrolysis and photolysis for functional nanoparticle growth

We report on an optical investigation of the pyrolysis and photolysis of trimethylindium (TMIn) as a typical metalorganic precursor for functional nanowire growth, aiming at an in-depth understanding of the governing chemistry and optimization of aerosol-based (aerotaxy) and epitaxial growth processes. A flow reactor with special consideration given to optical access was built to provide the chemical environment for in situ optical measurements on the pyrolysis and photolysis of TMIn. By probing a resonant transition of the indium atom, high-resolution laser absorption and laser-induced fluorescence spectroscopy were applied to obtain the atomic indium concentration at different chosen conditions in a spatially and temporally resolved manner. The results indicate that quantitative measurements of indium atoms under growth conditions are feasible. A 213 nm pulsed laser was employed to induce photolytic dissociation of TMIn vapor under chosen conditions. The photolytic dissociation of TMIn vapor with an ultraviolet laser turns out to be a promising method in generating substantial chemical effects, indicated by the generation of visible clouds of indium particles, and high concentrations of indium atoms far beyond the pyrolytically generated amount.

High-resolution laser-induced fluorescence spectroscopy of 28Si16O+ and 29Si16O+ in a cryogenic buffer-gas cell

The electronic, laser-induced fluorescence spectrum of the B2Σ+←X2Σ+ transition in 28Si16O+ and 29Si16O+ has been recorded in a cryogenic buffer gas cell at ≈100 K. Molecular constants are extracted for both 28Si16O+ and 29Si16O+, including the Fermi contact hyperfine constant for both the B and X states of 29Si16O+, and used in a discussion of the suitability of SiO+ in future quantum information experiments.

LNAPL saturation derived from laser induced fluorescence method

Light non-aqueous-phase liquid (LNAPL) spills are a widespread source of contamination in shallow aquifers. Owing to their human health risks, remediation actions should be undertaken to recover the contaminants from the subsurface. However, traditional investigation techniques do not assess the actual volume of residual hydrocarbon in the pore space, hindering the effectiveness of remediation predictions. The emergence of the high-resolution laser-induced fluorescence (LIF) technique has allowed the extent of NAPL migration and distribution to be determined in the field. Despite the good potential of LIF, this technique has not yet been used to quantify the volume or saturation of NAPL in porous media. By conducting medium-scale spill experiments, efforts have been undertaken to identify the empirical fluorescence signal relationship between LIF and LNAPL saturation. The comparison of both parameters indicates that LIF can predict the LNAPL saturation following an exponential function. However, owing to the high variability of the composition of LNAPL and the weathering stage, empirical coefficients to predict the saturation of LNAPL by fluorescence intensity are site-dependent. The measurement of saturation by LIF opens the possibility of more precise LNAPL volume estimation, including complex NAPL distribution scenarios.

Hyperfine analysis of the (2, 0) [18.3]3-X3Δ3 transition of cobalt monoboride

High-resolution laser-induced fluorescence spectra of the (2, 0) [18.3]3-X3Δ3 transition of cobalt monoboride (CoB) have been recorded. We report updated rotational parameters for both the [18.3]3 (v′ = 2) and X3Δ3 (v″ = 0) states of Co11B, as well as newly determined hyperfine interaction parameters. The observed hyperfine splitting is mainly due to the nuclear spin of 59Co (I = 7/2, μ/μN = 4.627); the 11B (I = 3/2, μ/μN = 2.689) interaction only results in broadening of the individual hyperfine transitions. The magnetic hyperfine constants help confirm the ground state electronic configuration, (8σ)2(3π)4(1δ)3(9σ)1, and provide more insight into the configurational mixing in the excited state.

Single-mode scannable nanosecond Ti:sapphire laser for high-resolution two-photon absorption laser-induced fluorescence (TALIF)

A pulsed Ti:sapphire laser has been developed so as to operate over a wide range of frequencies, even far from the optimum wavelength (790 nm), as a narrow-band light source for TALIF experiments on O, Cl, N and H. The coupling of the optical cavity, both to its injection seeder and to the laser output beam, relies on a reflecting plate, which makes it fundamentally easier to control the coupling coefficient over a wider spectral range than with an ordinary transmission coupler. Two intra-cavity prisms are used to bring the green pumping light longitudinally coincident with the cavity axis, inside the Ti:sapphire crystal. Seeding by a CW Ti:sapphire laser has made it possible to obtain single-mode emission over the whole range of tunability, thanks to the spectral selection of the prisms and to a specifically developed digital/analog controller. Experiments carried out with the system on oxygen atoms inside an oxygen plasma show that the experimental bandwidth is limited essentially by the collisional dephasing rate and the finite pulse duration.

Asymmetry of velocity distribution function and inhomogeneity-induced flow associated with neutral depletion structure in an ECR plasma

A neutral depletion structure with strong inhomogeneity in the radial direction has been observed in an electron cyclotron resonance plasma. We have measured the velocity distribution function of neutrals with a high resolution laser-induced fluorescence system and examined the relationship between asymmetry of distribution function and flow induced by inhomogeneity. It has been revealed that the third order moment of distribution function, that is, skewness, is proportional to the inhomogeneity-induced flow, and a simple relation between the skewness and the normalized flow velocity has been obtained and confirmed in the experiment.

Characterization of the [18.42]0+ – X1Σ+ (0, 0) band of tantalum nitride, TaN

High resolution laser-induced fluorescence (LIF) spectra of the [18.42]0+ − X1Σ+ (0,0) band of tantalum nitride, TaN, near 543nm, have been recorded and analyzed field-free and in the presence of a static electric field. The nuclear electric quadrupole hyperfine structure due to 181Ta(I=7/2) was resolved and analysis of the field-free spectrum yielded nuclear electric quadrupole coupling constants, eQq0, of −0.24025(75)cm−1 and −0.05755(76)cm−1 for the X1Σ+ and [18.42]0+ states, respectively. The Stark tuning of the R(0) and P(1) lines was analyzed to determine the magnitude of the molecular frame electric dipole moments, |μ→el|, of 3.33(4)D and 4.48(3)D for the X1Σ+ and [18.42]0+ states, respectively. The |μ→el| and eQq0 values are discussed in terms of predicted molecular orbitals for the X1Σ+ and [18.42]0+ states.

Laser spectroscopy of the Ã(2)Σ(+)-X̃(2)Πi band system of l-SiC3H.

The Ã(2)Σ(+)-X̃(2)Πi band system of l-SiC3H in the region 14,700-16,300 cm(-1) was re-investigated by laser induced fluorescence (LIF) and fluorescence depletion spectroscopy. Rotational analyses were made for three intense bands 0(0)(0), 4(0)(1), and 6(0)(1)7(0)(1) by observing high-resolution LIF excitation spectra. The determined rotational constants demonstrate that SiC3H is linear in the à state, as is the case in the X̃ state, and the observed band types are consistent with the vibrational assignments. The ν3(″) (C1-C2 stretch) level was identified in a newly observed dispersed fluorescence spectrum from the zero-vibrational level of the à state.

Gas temperature measurements in oxygen plasmas by high-resolution Two-Photon Absorption Laser-induced Fluorescence

One of the most important, and difficult to measure, parameters of laboratory discharges in molecular gases is the gas translational temperature. We propose a novel technique to measure directly, with excellent spatial and temporal resolution, the velocity distribution of ground-state atoms (oxygen atoms in this case) in plasmas from the Doppler broadening of their laser excitation spectra. The method is based on the well-known Two-Photon Laser-induced Fluorescence (TALIF) technique, but uses a specially-built pulsed tunable ultraviolet laser with very narrow bandwidth which allows the Doppler profiles to be measured with high precision. This laser consists of a pulsed Nd:YAG-pumped Ti:Sapphire ring cavity which is injection-seeded by a single-mode cw Ti:sapphire laser. The single-mode infrared output pulses are frequency quadrupled by two non-linear crystals to reach the necessary UV wavelength (226 nm, 0.2 mJ) for TALIF excitation. This technique should be applicable to a wide range of discharges, ranging from low-pressure RF plasmas for surface processing to atmospheric pressure plasmas. Results of preliminary tests on low-pressure O2 DC discharges are presented.

Hyperfine Interactions and Electric Dipole Moments in the [16.0]1.5(v = 6), [16.0]3.5(v = 7), and X2Δ5/2 States of Iridium Monosilicide, IrSi

The (6,0)[16.0]1.5-X(2)Δ(5/2) and (7,0)[16.0]3.5-X(2)Δ(5/2) bands of IrSi have been recorded using high-resolution laser-induced fluorescence spectroscopy. The field-free spectra of the (191)IrSi and (193)IrSi isotopologues were modeled to generate a set of fine, magnetic hyperfine, and nuclear quadrupole hyperfine parameters for the X(2)Δ(5/2)(v = 0), [16.0]1.5(v = 6), and [16.0]3.5 (v = 7) states. The observed optical Stark shifts for the (193)IrSi and (191)IrSi isotopologues were analyzed to produce the permanent electric dipole moments, μ(el), of -0.414(6) D and 0.782(6) D for the X(2)Δ(5/2) and [16.0]1.5 (v = 6) states, respectively. Properties of the X(2)Δ(5/2) state computed using relativistic coupled-cluster methods clearly indicate that electron correlation plays an essential role. Specifically, inclusion of correlation changes the sign of the dipole moment and is essential for achieving good accuracy for the nuclear quadrupole coupling parameter eQq0.

The molecular frame electric dipole moment and hyperfine interactions in hafnium fluoride, HfF

The (1,0) [17.9]2.5-X(2)Δ(3∕2) band of hafnium monofluoride (HfF) has been recorded using high-resolution laser-induced fluorescence spectroscopy both field-free and in the presence of a static electric field. The field-free spectra of (177)HfF, (179)HfF, and (180)HfF were modeled to generate a set of fine and hyperfine parameter for the X(2)Δ(3∕2)(v = 0) and [17.9]2.5 (v = 1) states. The observed optical Stark shifts for the (180)HfF isotopologue were analyzed to produce the molecular frame electric dipole moments of 1.66(1) D and 0.419(7) D for the X(2)Δ(3∕2) and [17.9]2.5 state, respectively. Both the generalized effective core potential and all-electron four component approaches were used in ab initio calculations to predict the properties of ground state HfF including equilibrium distance, dipole moments, quadrupole coupling, and magnetic hyperfine constants.

A combined crossed-beam and theoretical study of the reaction dynamics of O(3P) + C2H3 → C2H2 + OH: Analysis of the nascent OH products with the preferential population of the Π(A′) component

The gas-phase reaction dynamics of ground-state atomic oxygen [O((3)P) from the photo-dissociation of NO(2)] with vinyl radicals [C(2)H(3) from the supersonic flash pyrolysis of vinyl iodide, C(2)H(3)I] has been investigated using a combination of high-resolution laser-induced fluorescence spectroscopy in a crossed-beam configuration and ab initio calculations. Unlike the previous gas-phase bulk kinetic experiments by Baulch et al. [J. Phys. Chem. Ref. Data 34, 757 (2005)], a new exothermic channel of O((3)P) + C(2)H(3) → C(2)H(2) + OH (X (2)Π: υ" = 0) has been identified for the first time, and the population analysis shows bimodal nascent rotational distributions of OH products with low- and high-N" components with a ratio of 2.4:1. No spin-orbit propensities were observed, and the averaged ratios of Π(A('))∕Π(A") were determined to be 1.66 ± 0.27. On the basis of computations at the CBS-QB3 theory level and comparison with prior theory, the microscopic mechanisms responsible for the nascent populations can be understood in terms of two competing dynamical pathways: a direct abstraction process in the low-N" regime as the major pathway and an addition-complex forming process in the high-N" regime as the minor pathway. Particularly, during the bond cleavage process of the weakly bound van der Waals complex C(2)H(2)-OH, the characteristic pathway from the low dihedral-angle geometry was consistent with the observed preferential population of the Π(A') component in the nascent OH products. A molecular-level discussion of the reactivity, mechanism, and dynamical features of the title reaction are presented together with a comparison to gas-phase oxidation reactions of a series of prototypical hydrocarbon radicals.

Analysis of Nascent Rotational Energy Distributions and Reaction Mechanisms of the Gas-Phase Radical-Radical Reaction O(3P)+(CH3)2CH→C3H6+OH

This paper reports on the gas-phase radical-radical dynamics of the reaction of ground-state atomic oxygen [O((3)P), from the photodissociation of NO(2)] with secondary isopropyl radicals [(CH(3))(2)CH, from the supersonic flash pyrolysis of isopropyl bromide]. The major reaction channel, O((3)P)+(CH(3))(2)CH→C(3)H(6) (propene)+OH, is examined by high-resolution laser-induced fluorescence spectroscopy in crossed-beam configuration. Population analysis shows bimodal nascent rotational distributions of OH (X(2)Π) products with low- and high-N'' components in a ratio of 1.25:1. No significant spin-orbit or Λ-doublet propensities are exhibited in the ground vibrational state. Ab initio computations at the CBS-QB3 theory level and comparison with prior theory show that the statistical method is not suitable for describing the main reaction channel at the molecular level. Two competing mechanisms are predicted to exist on the lowest doublet potential-energy surface: direct abstraction, giving the dominant low-N'' components, and formation of short-lived addition complexes that result in hot rotational distributions, giving the high-N'' components. The observed competing mechanisms contrast with previous bulk kinetic experiments conducted in a fast-flow system with photoionization mass spectrometry, which suggested a single abstraction pathway. In addition, comparison of the reactions of O((3)P) with primary and tertiary hydrocarbon radicals allows molecular-level discussion of the reactivity and mechanism of the title reaction.

High-resolution turbulent scalar field measurements in an optically accessible internal combustion engine

High-resolution planar laser-induced fluorescence (PLIF) measurements were performed in an optically accessible internal combustion engine to investigate the evolution of the turbulent mixing process during the intake and compression strokes. The PLIF measurements were used to analyze the important turbulent length scales, scalar energy and dissipation spectra, and mean scalar gradients. The fluorescence images had sufficient spatial resolution and integrity to resolve all of the fine-scale features of the flow, allowing for direct determination of the Batchelor length scale. The integral and Taylor scales were also determined from two-point spatial correlations of the fluctuating scalar field using an appropriately defined mean scalar value. The general morphology of the scalar field and the measured integral, Taylor and Batchelor length scales were found to be largely independent of engine speed and intake pressure, but increased as the engine cycle progressed through the intake and compression strokes. The measured Batchelor scales ranged from 22 to 54 μm; the integral scales ranged from 1.8 to 3.5 mm; and the Taylor microscales ranged from 0.6 to 1.2 mm. The Taylor and integral scale values were comparable to values reported in the literature from in-cylinder velocity measurements. The mean scalar gradient, a measure of the fine-scale mixing rate, monotonically decreased as the engine cycle advanced. High-resolution measurements of this type are important in the development and validation of future engine combustion models used in computer simulations.

Molecular-beam optical Stark and Zeeman study of theA2Π--X2Σ+(0,0) band system of BaF

The $A{ }^{2}\ensuremath{\Pi}\ensuremath{-}X{ }^{2}{\ensuremath{\Sigma}}^{+}$ (0,0) band system of barium monofluoride (BaF) has been recorded using high-resolution laser-induced fluorescence spectroscopy both field-free and in the presence of static magnetic and electric fields. The field-free spectra for the $^{135}\mathrm{Ba}$F, $^{137}\mathrm{Ba}$F, and $^{138}\mathrm{Ba}$F isotopologues were modeled to generate an improved set of spectroscopic constants for the $A{ }^{2}$\ensuremath{\Pi}($\ensuremath{\upsilon}$ $=$ 0) and $X{ }^{2}$\ensuremath{\Sigma}${}^{+}$($\ensuremath{\upsilon}$ $=$ 0) states. The observed optical Stark shifts for the $^{138}\mathrm{Ba}$F isotopologue were analyzed to produce the permanent electric dipole moments of 1.50(2) and 1.31(2) D for the $A{ }^{2}$\ensuremath{\Pi}${}_{1/2}$($\ensuremath{\upsilon}$ $=$ 0) and $A{ }^{2}$\ensuremath{\Pi}${}_{3/2}$ ($\ensuremath{\upsilon}$ $=$ 0) states, respectively. The observed optical Zeeman shifts for the $^{138}\mathrm{Ba}$F isotopologue were analyzed to produce a set of magnetic $g$ factors for the $A{ }^{2}$\ensuremath{\Pi}($\ensuremath{\upsilon}$ $=$ 0) and $X{ }^{2}$\ensuremath{\Sigma}${}^{+}$($\ensuremath{\upsilon}$ $=$ 0) states.

Subgrid scale scalar variance in high-Schmidt-number turbulence

The subgrid scale (SGS) variance for a high-Schmidt-number passive scalar of Sc >> 1 is measured using a high-resolution planar laser-induced fluorescence technique in a grid-generated turbulent liquid flow, and the values of the model coefficients in the scale-similarity model and the scalar-gradient model used for estimating the SGS scalar variance are experimentally evaluated. The results show that for both models, the measured values are much larger than the well-known values obtained in the previous studies done for non-high-Sc scalars of Sc ≅ 1. Similarly, the measured value of the model coefficient in the scalar-gradient model tends to be larger than the value estimated by the dynamic procedure. The increases in the measured values of the model coefficients for the high-Sc scalar can be explained by the presence of the viscous-convective range showing a nearly (−1)-slope in the high-wavenumber range of the power spectrum of concentration fluctuation. © 2011 American Institute of Chemical Engineers AIChE J, 2012

A gas-phase crossed-beam study of OH produced in the radical–radical reaction of O(3P) with iso-propyl radical (CH3)2CH

The gas-phase radical-radical reaction dynamics of ground-state atomic oxygen [O((3)P)] with iso-propyl radicals, (CH(3))(2)CH, were investigated by applying a combination of high-resolution laser-induced fluorescence spectroscopy in a crossed-beam configuration and ab initio calculations. The nascent distributions of OH (X(2)Π: υ'' = 0) from the major reaction channel O((3)P) + (CH(3))(2)CH → C(3)H(6) (propene) + OH showed substantial internal excitations with a bimodal feature of low- and high-N'' components with neither spin-orbit nor Λ-doublet propensities. Unlike previous kinetic results, proposed to proceed only through the direct H-atom abstraction process, on the basis of the population analysis and comparison with the statistical theory, the title reaction can be described in terms of two competing mechanisms at the molecular level: direct abstraction process and indirect short-lived addition-complex-forming process with a ratio of 1.25 : 1.