Laser-induced Fluorescence Excitation Research Articles

Conformational preference of 2-(4-methoxyphenyl)ethanol studied by supersonic jet spectroscopy: Intramolecular OH/π interaction.

A π-type hydrogen bonding between the OH group and the π electron is a crucial factor for the conformational preference of the molecular structure with a flexible group. However, the information on the effect of the substituent on the OH/π interaction is insufficient. The laser-induced fluorescence (LIF) excitation, the dispersed fluorescence (DF), the IR-UV hole-burning, and the IR dip spectra of jet-cooled 2-(4-methoxyphenyl)ethanol were measured for the first time. Almost all bands observed in the spectral region of 35 550-36 500cm-1 in the LIF excitation spectrum were successfully assigned with the DF and the IR-UV hole-burning spectra coupled with the quantum chemical calculation at M06-2x/6-311G and MP2/6-311G levels. Five conformers were found in the LIF excitation spectrum. The most stable conformer was Ggπ, and the second most stable conformer was Ggπ' (the trans rotamer of the methoxy group for Ggπ). Ggπ and Ggπ' had the OH group directed toward the π electron system of the benzene ring. The OH stretching frequency of Ggπ/Ggπ' of MPE in the IR dip spectra was red-shifted against that of Ggπ of phenylethanol, indicating that the introduction of the methoxy group would enhance the intramolecular OH/π interaction. In addition, the torsional vibration between the benzene ring and the side chain (-CH2CH2OH) (mode 63) was observed in the DF spectra of the Ggπ-00 and Ggπ'-00 band excitation, but their intensities were rather different, resulting from the different orientation of the OH group for each conformer toward the π electron system. The methoxy group would increase the negative charge on the benzene ring and would enhance the intramolecular OH/π interaction through the electrostatic interaction.

Фототераностика тяжелых дисплазий и преинвазивного рака шейки матки

Due to the high prevalence of pre-cancerous cervical diseases and cervical cancer, the search, pathogenetic reasoning and evaluation of the efficacy of new approaches to the diagnosis and treatment of these pathologies, including those aimed at fertility preservation, are extremely relevant. Objective. To study the clinical efficacy and safety of phototheranostics as a method of diagnosis and treatment of severe dysplasia and pre-invasive cervical cancer. Patients and methods. An open-label, retrospective-prospective, randomized, comparative, clinical trial involving 94 reproductive-aged patients with morphologically confirmed severe cervical intraepithelial neoplasia (CIN) and pre-invasive cervical cancer was conducted. All patients were divided into two groups: group 1 (comparison) included 49 patients who underwent cervical conization with curettage of the remaining cervical canal; group 2 (study) included 45 patients who underwent phototheranostics: photodynamic therapy (PDT) with simultaneous laser-induced fluorescence excitation. Results. After the first course of phototheranostics, most women in the study group had normal cytological results, which were observed 6, 9, and 12 months after treatment. In these periods, all patients who underwent phototheranostics had a normal colposcopic picture, while in the comparison group, some patients showed signs of cervical lesions. Morphological confirmation of the complete therapeutic effect was considered to be elimination of human papillomavirus (HPV) and normalization of the proliferative activity of the epithelial layer (assessed by the levels of Ki-67 and phosphohistone markers) during phototheranostics. Conclusion. The study demonstrated the high clinical efficacy of phototheranostics in the treatment of CIN and pre-invasive cervical cancer: 85–88% of women achieved the desired therapeutic effect after the first session of phototheranostics, and after the second session, all patients in the study group had complete regression of cervical mucosal lesions. In the study group, higher pregnancy rates and favourable outcomes in patients planning pregnancy confirmed that the use of PDT contributes to fertility preservation in women treated for CIN and pre-invasive cervical cancer, which is associated with the preservation of anatomo-functional characteristics of the cervix when using phototheranostics. Key words: PDT, HPV, photodynamic therapy, fluorescence diagnosis, cervical dysplasia, photosensitizers, pre-invasive cervical cancer, phototheranostics, pregnancy after PDT

Multi-line OH-LIF for gas-phase temperature and concentration imaging in the SpraySyn burner

Gas-phase temperature and OH concentration images are measured in the SpraySyn nanoparticle-synthesis standard burner using multi-line OH laser-induced fluorescence (LIF) thermometry. In this burner, a spray flame fed by a combustible nanoparticle precursor solution is stabilized by a surrounding axisymmetric lean premixed laminar methane/oxygen pilot flame. For measuring OH rotational temperature, the laser is scanned across the 282.05–282.17 nm range and LIF excitation spectra are fitted for each image pixel by simulated spectra. Temperature maps are determined for the pilot flame and the ethanol spray flame with variable dispersion gas flow rates of oxygen used in the two-fluid nozzle. The addition of 2-EHA (2-ethylhexanoic acid) to the solution was found to increase the flame temperature. Laser attenuation across the flame was measured using simultaneous recordings of the fluorescence of uranine/water solution from two dye cuvettes illuminated with the laser sheet before and after the flame and the effect of attenuation was quantified. Absolute OH concentration distributions are determined by combining the LIF images, laser attenuation measurements, and derived temperature distributions. The temporal stability of the flame is investigated for various operating conditions by statistical evaluation of recorded instantaneous OH-LIF images.

Optical spectroscopy of CrO and electronic states of the Cr group metal monoxides

All of the experimentally known electronic states of the Cr group metal monoxides (CrO, MoO, and WO) have been presented in the paper. The optical spectra of the CrO molecule have been investigated in the gas phase through a combination of the laser-induced fluorescence (LIF) excitation and single-vibronic-level (SVL) emission spectroscopy in the supersonic expansion. The rotational constants of the vibronic electronic states, including X5Π−1 (v″ = 0–3), B5Π−1 (v′ = 0–10), and B5Π1 (v′ = 1, 5), and the vibrational constants of the spin–orbit components X5Π−1,0,1 have been obtained. The molecular constants of the MoO and WO molecules have been summarized by reviewing the previous spectroscopic studies, and a comprehensive energy level diagram of the Cr group metal monoxides has been constructed. By comparing the electronic configurations, bond lengths, and vibrational frequencies of all the transition metal monoxides in the ground electronic state, the significance of the relativistic effect in the bonding of the 5d transition metal monoxides has been discussed. The related spectroscopic data of the CrO molecule are available at https://doi.org/10.57760/sciencedb.j00113.00085.

Fine and hyperfine interactions of PbF studied by laser-induced fluorescence spectroscopy.

The fine and hyperfine interactions in PbF have been studied using the laser-induced fluorescence (LIF) spectroscopy method. Cold PbF molecular beam was produced by laser-ablating a Pb rod under jet-cooled conditions, followed by the reaction with SF6. The LIF excitation spectrum of the (0, 0) band in the B2Σ+-X2Π1/2 system of the 208PbF, 207PbF, and 206PbF isotopologues has been recorded with rotational, fine structure, and hyperfine-structure resolution. Transitions in the LIF spectrum were assigned and combined with the previous X2Π3/2-X2Π1/2 emission spectrum in the near-infrared region [Ziebarth et al., J. Mol. Spectrosc. 191, 108-116 (1998)] and the X2Π1/2 state pure rotational spectrum of PbF [Mawhorter et al., Phys. Rev. A 84, 022508 (2011)] in a global fit to derive the rotational, spin-orbit, spin-rotation, and hyperfine interaction parameters of the ground (X2Π1/2) and the excited (B2Σ+) electronic states. Molecular constants determined in the present work are compared with previously reported values. Particularly, the significance of the hyperfine parameters, A⊥ and A‖, of 207Pb is discussed.

Electronic structure of RuO

The laser-induced fluorescence excitation spectra and single-vibronic-level emission spectra of ruthenium monoxide (RuO) molecule have been investigated using laser ablation of a ruthenium target and reaction with a free jet expansion of oxygen. Sixteen excitation bands have been experimentally observed in the energy range of 13,800 – 19,250 cm–1 and grouped into transition systems from the ground X5Δ4 and X5Δ3 states to six excited electronic states. The molecular constants, including the spin-orbit splittings, the rotational constants and the vibrational frequencies, in the ground and excited electronic states were obtained through rotational analysis of the spectra. The electronic structure has been discussed based on high-level ab initio calculations.

Excitation dynamics in polyacene molecules on rare-gas clusters.

Laser-induced fluorescence spectra and excitation lifetimes of anthracene, tetracene, and pentacene molecules attached to the surface of solid argon clusters have been measured with respect to cluster size, density of molecules, and excitation density. Results are compared to previous studies on the same sample molecules attached to neon clusters. A contrasting lifetime behavior of anthracene on neon and argon clusters is discussed, and mechanisms are suggested to interpret the results. Although both neon and argon clusters are considered to be weakly interacting environments, we find that the excitation decay dynamics of the studied acenes depends significantly on the cluster material. Moreover, we find even qualitative differences regarding the dependence on the dopant density. Based on these observations, previous assignments of collective radiative and non-radiative decay mechanisms are discussed in the context of the new experimental findings.

Laser-induced-fluorescence imaging of a spin-polarized ultracold neutral plasma in a magnetic field

We report Doppler-sensitive laser-induced-fluorescence (LIF) imaging of an ultracold neutral plasma in a magnetic field. Local values of ion density, hydrodynamic fluid velocity, temperature, and spin polarization are obtained using a fluorescence model based on velocity-resolved rate equations (REs) including the transfer of ions between states due to laser coupling and spontaneous emission. The RE approach captures optical pumping of ions into states that are not driven by the LIF excitation laser, and this is validated with experimental data. Combined molecular-dynamics and quantum-trajectories simulations verify that velocity-changing collisions have a negligible impact on the state population evolution for typical experimental conditions. Relative intensities of Zeeman components of the LIF spectra provide clear evidence that the ions are electron-spin-polarized when created by photoionization of magnetically trapped $^{88}\mathrm{Sr}$ atoms. This probe opens many possibilities for studying thermal transport and the equilibration of neutral plasmas in overlapping regimes of strong coupling and magnetization.

Spectroscopic Study of the B 1Π State of NaH.

In this study, the B1Π excited state of NaH has been experimentally studied for the first time. Pulsed laser-induced fluorescence excitation spectroscopy was used to investigate the B1Π electronic state of NaH. A total of 48 ro-vibronic transitions were observed, including within the B–X (0–0) and B–X (0–1) transition bands. Only one B-state vibrational level was identified, and a series of PQR lines, with eight e-parity and eight f-parity sublevels (v′ = 0, J′ = 1–8), were assigned. The level assignment was supported by a comparison of the experimental line positions with the ab initio calculations, the dispersed laser-induced fluorescence spectrum of the NaH B1Π → X1∑+ emission, and the V-type optical–optical double resonance spectra. The Dunham-type coefficients, the mean internuclear distance, the harmonic vibrational frequency ω, and the dissociation energies D0 and De of the B1Π state were determined.

Fine and hyperfine interactions in 171YbOH and 173YbOH.

The odd isotopologues of ytterbium monohydroxide, 171,173YbOH, have been identified as promising molecules to measure parity (P) and time reversal (T) violating physics. Here, we characterize the Ã2Π1/2(0,0,0)-X̃2Σ+(0,0,0) band near 577nm for these odd isotopologues. Both laser-induced fluorescence excitation spectra of a supersonic molecular beam sample and absorption spectra of a cryogenic buffer-gas cooled sample were recorded. In addition, a novel spectroscopic technique based on laser-enhanced chemical reactions is demonstrated and used in absorption measurements. This technique is especially powerful for disentangling congested spectra. An effective Hamiltonian model is used to extract the fine and hyperfine parameters for the Ã2Π1/2(0,0,0) and X̃2Σ+(0,0,0) states. A comparison of the determined X̃2Σ+(0,0,0) hyperfine parameters with recently predicted values [Denis et al., J. Chem. Phys. 152, 084303 (2020); K. Gaul and R. Berger, Phys. Rev. A 101, 012508 (2020); and Liu et al., J. Chem. Phys. 154,064110 (2021)] is made. The measured hyperfine parameters provide experimental confirmation of the computational methods used to compute the P,T-violating coupling constants Wd and WM, which correlate P,T-violating physics to P,T-violating energy shifts in the molecule. The dependence of the fine and hyperfine parameters of the Ã2Π1/2(0,0,0) and X̃2Σ+(0,0,0) states for all isotopologues of YbOH are discussed, and a comparison to isoelectronic YbF is made.

Spin-orbit splittings in the low-lying states of MoO molecule

The laser-induced fluorescence (LIF) excitation spectra and single vibronic level (SVL) emission spectra of the jet-cooled molybdenum monoxide (MoO) molecule in the gas phase have been investigated in the range of 16,500–23,200 cm−1. Totally 11 rotationally resolved excitation spectra have been observed, and the rotational constants in 10 upper excited states and 4 lower spin-orbit components of the ground X5Π state have been obtained. In addition, 10 spin-orbit components in the ground X5Π state, the first and second excited states a3Σ− and b3∆, have been identified in the emission spectra. Ab initio calculations have been performed and used to identify the observed low-lying states.

Laser-induced fluorescence spectroscopy of uranium monofluoride

The laser-induced fluorescence excitation spectra of uranium monofluoride have been recorded in the range of 17000-19000 cm−1 using two-dimensional spectroscopy. High resolution dispersed fluorescence spectra and time-resolved fluorescence spectroscopy were also recorded. Three rotationally resolved bands were intensively analyzed, and all bands were found to be derived from the ground state X(1)4.5 with a rotational constant of 0.23421 cm−1. The low-lying electronic states were observed near 435 and 651 cm−1 in the dispersed fluorescence spectra, which were assigned as Ω′ = 3.5 and 2.5, respectively. The vibrational constants for the X(1)4.5 and X(1)3.5 states were calculated. The branching ratios of the dispersed fluorescence spectra for the [18.62]3.5, [17.72]4.5, and [17.65]4.5 states were reported. Radiative lifetime of 332(9) ns, 825(49) ns, and 433(15) ns for the [18.62]3.5, [17.72]4.5, and [17.65]4.5 states were obtained by fitting the time-resolved fluorescence spectroscopy, respectively. Transition dipole moments were performed using the branching ratios and the radiative lifetimes.

New aspect of photophysics of 7,7,8,8-tetracyanoquinodimethane and its solvated complexes: intra- vs. inter-molecular charge-transfer.

We performed laser-induced fluorescence (LIF) spectroscopy of 7,7,8,8-tetracyanoquinodimethane (TCNQ) and its solvated complexes with acetonitrile (ACN) and benzene (Bz), under the jet-cooled gas-phase condition. We also carried out fluorescence and its time profile measurements in TCNQ/Bz/hexane solution to compare with the gas-phase results. The LIF excitation spectrum of the S1 (ππ*)–S0 electronic transition of TCNQ monomer exhibited unusual vibronic structure with the maximum intensity at ∼3000 cm−1 above the band origin. In addition, the fluorescence lifetime is more than 100 times longer than that in hexane solution with most of the bands showing double exponential decay. The unusual feature of the vibronic bands is intrinsic and not due to the presence of other species, as confirmed by UV-UV hole-burning (HB) spectroscopy. These unusual features of S1 are thought to be due to the coupling with the S2 state, where S2 was revealed to have intramolecular charge-transfer (ICT) character. The S1–S0 transition of the TCNQ–ACN complex exhibited sharp vibronic bands which are red-shifted by 120 cm−1 from those of the monomer, indicating van der Waals (vdW) interaction between them; however, the fluorescence lifetime was drastically shortened. In contrast, the TCNQ–Bz complex gave a broad electronic spectrum. The study of the fluorescence and its time profile in TCNQ/Bz/hexane solution clearly shows the formation of the CT complex between TCNQ and Bz. Based on the experimental results and density functional theory (DFT) calculations, we propose that in the TCNQ monomer and TCNQ–ACN complex the S1 (ππ*) state is coupled to the intramolecular CT state, while the S1 state of TCNQ in the TCNQ–Bz complex is more strongly coupled to the intermolecular CT state.

The electronic structure of WS molecule below 21,500 cm−1

The low-lying electronic states of the tungsten monosulfide (WS) molecule have been investigated using laser-induced fluorescence excitation spectra and high-level ab initio calculations. 29 vibronic bands in total are experimentally observed in the range of 13,100 – 21,500 cm−1 and grouped into 8 electronic transition systems. The spectroscopic constants including the vibrational frequency, rotational constant and radiative lifetime in the low-lying excited electronic state are obtained by analysis of the rovibrational-resolved spectra. Seven lowest Ω sub-states that belong to the lowest three Λ-S states considering the spin-orbit effect, i.e. the ground state 3Σ−, first and second excited states 5Π and 3Φ, are identified through single-vibrational-level emission spectra. In addition, seven Ω = 1 excited sub-states in the visible energy range are identified, which are consecutively consistent with the ab initio calculation results of the sixth to twelfth Ω = 1 sub-states. The experimental and theoretical results on WS molecule may provide a benchmark to study the electronic structure of those molecules with strong spin-orbit coupling and electron-electron correlation.

Genetic Algorithm for quick finding of diatomic molecule potential parameters

ABSTRACT Application of Genetic Algorithm (GA) for determination of parameters of an analytical representation of diatomic molecule potential is presented. GA can be used for finding potential characteristics of an electronic energy state which can be described by an analytical function. GA was tested on two artificially generated datasets which base on potentials with known characteristics and two laser induced fluorescence excitation spectra recorded using transitions in CdKr and CdAr molecules. Tests on generated datasets showed that GA can properly reproduce parameters of the potentials. Tests on experimental spectra indicated that changing the potential model from a Morse, which is frequently used as a starting potential in the inverse perturbation approach method, to an expanded Morse oscillator leads to noticeable improvement of agreement between simulated and experimental data.

Probing the Endo/Exo Isomeric Variants of a Binary Complex of Cyclopropylamine with p-Fluorophenol by LIF Spectroscopy: A Comparative Study with Ammonia Complex.

Conformational isomers of an O-H···N hydrogen-bonded binary complex between para-fluorophenol (pFP) and a nonrigid primary amine base, cyclopropylamine (CPA), have been probed by means of laser-induced fluorescence (LIF) spectroscopy in a supersonic jet expansion. Two closely spaced electronic origin bands have been identified in the measured LIF excitation spectrum, and their assignments have been corroborated by making comparisons with the spectra of the parent pFP-NH3 complex recorded under the same expansion condition. The observation is consistent with the presence of endo and exo isomeric variants of the complex predicted by electronic structure theory methods, and the endo isomer is stabilized by ∼2 kcal/mol additionally owing to the formation of a C-H···O and a C-H···π type of weak hydrogen bonds between the two moieties. In the fluorescence excitation (FE) spectrum, the low-frequency bands for different intermolecular modes gain substantial intensity, and this spectral feature is in contrast to that of the pFP-NH3 complex. The Franck-Condon intensity of the bands has been simulated invoking Duschinsky rotation scheme, taking into consideration the ground- and excited-state geometries.

Branching Ratios, Radiative Lifetimes, and Transition Dipole Moments for YbOH.

Medium resolution (Δν̃ ∼ 3 GHz) laser-induced fluorescence (LIF) excitation spectra of a rotationally cold sample of YbOH in the 17300-17950 cm-1 range have been recorded using two-dimensional (excitation and dispersed fluorescence) spectroscopy. High resolution (Δλ ∼ 0.65 nm) dispersed laser-induced fluorescence (DLIF) spectra and radiative decay curves of numerous bands detected in the medium resolution LIF excitation spectra were recorded. The vibronic energy levels of the X̃2Σ+ state were predicted using a discrete variable representation approach and compared with observations. The radiative decay curves were analyzed to produce fluorescence lifetimes. DLIF spectra resulting from high resolution (Δν̃ < 10 MHz) LIF excitation of individual low-rotational lines in the Ã2Π1/2(0,0,0)-X̃2Σ+(0,0,0), Ã2Π1/2(1,0,0)-X̃2Σ+(0,0,0), and [17.73]Ω = 0.5(0,0,0)-X̃2Σ+(0,0,0) bands were also recorded. The DLIF spectra were analyzed to determine branching ratios which were combined with radiative lifetimes to obtain transition dipole moments. The implications for laser cooling and trapping of YbOH are discussed.

Spin-orbit splitting in the ground state of tungsten monosulfide

The laser-induced fluorescence (LIF) excitation spectra and single vibronic level (SVL) emission spectra of tungsten monosulfide (WS) molecule have been recorded in the range of 13,100–16,500 cm−1 using laser ablation/reaction free-jet expansion. 13 vibronic bands are observed and grouped into 3 electronic band systems including the [15.30]1–X0+, [15.10]1–X0+, and [a + 13.12]1–X1 transitions. The first two transition progressions are experimentally observed for the first time. When the previously observed electronic transition system [a + 12.92]1–X1 (Tsang et al., 2019) is also included, the four observed systems are assigned as the two spin-orbit components X0+ and X1 of the 3Σ− ground state to the two upper states [15.30]1 and [15.10]1. The spin-orbit splitting between the X0+ and X1 states is determined as 2λ = 2181.10(9) cm−1. The spin-orbit splitting in the ground electronic state and the primarily attributed Λ-S states in the excited states are discussed.

High-temperature continuous molecular beam source for aggressive elements: An example of zinc.

Expansion of Zn2 or ZnRg (Rg = rare gas atom) in a molecular supersonic beam constitutes a considerable technical challenge due to the high zinc melting point and high zinc reactivity with stainless steel at high temperatures. In order to overcome these difficulties and meet the requirements for spectroscopy of van der Waals molecules containing zinc, a high-temperature source-module of the supersonic molecular beam for aggressive elements was designed. The module was tested in the laser-induced fluorescence excitation spectroscopy experiment using the b30u +43P1←X10g +(41S0) bound ← bound transitions in Zn2. The new source-module can be used for other aggressive elements for which a laser-vaporization technique has been used to date.

Saturated laser-induced fluorescence in liquid kerosene seeded with a dye: influence of temperature and excitation intensity

Fluorescence-based techniques are commonly implemented to characterize droplet sprays in flows at temperature above 293 K. Nevertheless, in the case of gas turbine altitude relight, aeroengines are exposed to critical operating conditions where the liquid fuel temperature can reach values as low as − 40 °C. As a result, it is necessary to address the influence of this parameter on fluorescence intensity for temperatures below room values. In this paper, an innovative saturated laser-induced fluorescence (SLIF) excitation scheme is proposed to overcome the strong temperature dependence of fluorescence in liquid kerosene seeded with a dye. The findings of this work are based on gated sequential images recorded with an intensified camera during and after the laser pulse duration so as to sample the temporal evolution of the fluorescence emission. The results show that, for low laser excitation intensity, the fluorescence intensity remains proportional to the laser power. However, a non-linear response is observed in the case of high excitation intensity. This difference can be used to limit the fluorescence dependence on temperature by carefully selecting the temporal window where fluorescence is detected. Finally, although the method presented in this paper is applied to cold liquid kerosene, its range of application can be extended to other liquids and other temperature ranges.