Time-dependent Fluorescence Intensity Research Articles

Quantification of gastric tube perfusion following esophagectomy using fluorescence imaging with indocyanine green

IntroductionAnastomotic leakage (AL) remains a prevalent and life-threatening complication after esophagectomy. Gastric tube perfusion assessment using indocyanine green fluorescence imaging (ICG-FI) has been published in several studies and appears to be a promising tool to reduce AL rates by changing the surgical approach, namely by an intraoperative evaluation of the anastomosis localization.MethodsIn this study, gastric tube perfusion was quantified by using ICG-FI in 20 high-risk patients undergoing esophagectomy. From a time-dependent fluorescence intensity curve, the following three parameters were evaluated: slope of fluorescence intensity (SFI), background subtracted peak fluorescence intensity (BSFI), and time to slope (TTS).ResultsThe values between pyloric region and tip showed a similar downward trend and SFI and BSFI significantly correlated with the distance to the pyloric region. SFI and BSFI were significantly decreased at the tip of the gastric tube. The placement of anastomosis in an area with homogenous fluorescence pattern was correlated with no AL in 92.9% of cases. An inhomogeneous fluorescence pattern at anastomotic site was a risk factor for the occurrence of an AL (p < 0.05). Reduction of perfusion up to 32% using SFI and up to 23% using BSFI was not associated with AL.ConclusionICG-FI can be used to quantify the gastric tube perfusion by calculating SFI, BSFI, and TTS. The anastomosis should be created in areas with homogeneous fluorescence pattern. A reduction in blood flow of up to 32% can be accepted without causing an increased rate of insufficiency.

Spiropyran Photoisomerization Dynamics in Multiresponsive Hydrogels.

Light-responsive, spiropyran-functionalized hydrogels have been used to create reversibly photoactuated structures for applications ranging from microfluidics to nonlinear optics. Tailoring a spiropyran-functionalized hydrogel system for a particular application requires an understanding of how co-monomer composition affects the switching dynamics of the spiropyran chromophore. Such gels are frequently designed to be responsive to different stimuli such as light, temperature, and pH. The coupling of these influences can significantly alter spiropyran behavior in ways not currently well understood. To better understand the influence of responsive co-monomers on the spiropyran isomerization dynamics, we use UV-vis spectroscopy and time-dependent fluorescence intensity measurements to study spiropyran-modified hydrogels polymerized from four common hydrogel precursors of different pH and temperature responsivity: acrylamide, acrylic acid, N-isopropylacrylamide, and 2-(dimethylamino)ethyl methacrylate. In acidic and neutral gels, we observe unusual nonmonotonic, triexponential fluorescence dynamics under 405 nm irradiation that cannot be explicated by either the established spiropyran-merocyanine interconversion model or hydrolysis. To explain these results, we introduce an analytical model of spiropyran interconversions that includes H-aggregated merocyanine and its light-triggered disaggregation under 405 nm irradiation. This model provides an excellent fit to the observed fluorescence dynamics and elucidates exactly how creating an acidic internal gel environment promotes the fast and complete conversion of the hydrophilic merocyanine speciesto the hydrophobic spiropyran form, which is desired in most light-sensitive hydrogel actuators. This can be achieved by incorporating acrylic acid monomers and by minimizing the aggregate concentration. Beyond spiropyran-functionalized gel actuators, these conclusions are particularly critical for nonlinear optical computing applications.

A novel fluorescent cardiac imaging system for preclinical intraoperative angiography

BackgroundIntraoperative coronary angiography can tremendously reduce early coronary bypass graft failures. Fluorescent cardiac imaging provides an advanced method for intraoperative observation and real-time quantitation of blood flow with high resolution.MethodsWe devised a system comprised of an LED light source, special filters, lenses and a detector for preclinical coronary artery angiography. The optical setup was implemented by using two achromatic doublet lenses, two positive meniscus lenses, a band-pass filter, a pinhole and a CCD sensor. The setup was optimized by Zemax software. Optical design was further challenged to obtain more parallel light beams, less diffusion and higher resolutions to levels as small as arterioles. Ex vivo rat hearts were prepared and coronary arteries were retrogradely perfused by indocyanine green (ICG). Video angiography was employed to assess blood flow and plot time-dependent fluorescence intensity curve (TIC). Quantitation of blood flow was performed by calculating either the gradient of TIC or area under curve. The correlation between blood flow and each calculated parameters was assessed and used to evaluate the quality of flow.ResultsHigh-resolution images of flow in coronary arteries were obtained as precise as 62 µm vessel diameter, by our custom-made ICG angiography system. The gradient of TIC was 3.4–6.3 s−1, while the area under curve indicated 712–1282 s values which ultimately gained correlation coefficients of 0.9938 and 0.9951 with relative blood flow, respectively.ConclusionThe present ICG angiography system may facilitate evaluation of blood flow in animal studies of myocardial infarction and coronary artery grafts intraoperatively.

Optical and impedimetric study of genetically modified cells for diclofenac sensing

Abstract. Whole-cell biosensors, based on genetically modified yeast cells, were employed to detect anthropogenic micropollutants (e.g. drugs). Specific stimuli, e.g. traces of drugs, lead to the induction of fluorescence in the respective cells. Receptors of the cells detect specific signal molecules and induce the formation of fluorescent proteins. In this work, genetically modified cells of the yeast Saccharomyces cerevisiae BY4741 were confined in a four-chamber microfluidic cell, providing an optical monitoring of the cell behaviour and their supply with the nutrients. The measurements of the time-dependent fluorescence intensity were performed with different concentrations of the drug diclofenac, and the sensitivity of yeast cells to diclofenac was demonstrated. Cell viability was monitored by simultaneous impedance recording.

Sortase-Mediated Surface Functionalization of Stimuli-Responsive Microgels.

In this work we explored an enzyme-mediated method for selective and efficient decoration of aqueous microgels with biomolecules. Poly(N-vinylcaprolactam) (VCL) microgels with varied amounts of glycidyl methacrylate (GMA) as comonomer incorporated in the microgel shell were synthesized and characterized in regard to their size, swelling degree, and temperature-responsiveness in aqueous solutions. The surface of the PVCL/GMA microgel containing 5 mol % glycidyl methyacrylate was modified by grafting of a specific recognition peptide sequence (LPETG) for Sortase A from Staphylococcus aureus (Sa-SrtAΔ59). Sortase-mediated conjugation of the enhanced Green Fluorescent Protein (eGFP) carrying a N-terminal triglycine tag to LPETG-modified microgels was successfully performed. Conjugation of eGFP to the microgel surface was qualitatively proven by confocal microscopy and by fluorescence intensity measurements. The developed protocol enables a precise control of the amount of eGFP grafted to the microgel surface as evidenced by the linear increase of fluorescence intensity of modified microgel samples. The kinetic of the sortase-mediated coupling reaction was determined by time-dependent fluorescence intensity measurements. In summary, sortase-mediated coupling reactions are a simple and powerful technique for targeted surface functionalization of stimuli-responsive microgels with biomolecules.

Fluorescence Intermittency in Monolayer WSe2**Supported by the National Basic Research Program of China under Grant No 2013CB922304, and the National Natural Science Foundation of China under Grant Nos 11474275, 61674135 and 91536101.

Fluorescence intermittent dynamics of single quantum emitters in monolayer WSe2 are investigated via measuring spectrally resolved time traces and time-dependent fluorescence intensity trajectories. Analysis of fluorescence trajectories and spectral shifting reveal a correlation between the fluorescence intermittency and spectral diffusion. A model of an inverse power law can be used to understand the observed blinking dynamics.

Distinction of non-ischemia inducing versus ischemia inducing coronary stenosis by fluorescent cardiac imaging.

Intraoperative fluorescent cardiac imaging (FCI) can quantitatively assess myocardial perfusion abnormalities produced by graded flow-limiting coronary stenosis (FLS), but there are no data to distinguish FLS from non flow-limiting stenosis (NFLS) to determine their functional significance. The aim of the study was to evaluate whether non-ischemia inducing NFLS can be quantified and differentiated from FLS by FCI technology. Data are compared to gold standard fluorescent microspheres (FM). 11 domestic pigs of either sex underwent sternotomy. Left anterior descending coronary artery blood-flow was recorded by transit-time flow measurements. After baseline and Adenosine-induced hyperemia, two stenosis of low severity (50 and 90 % NFLS) were produced, followed by FLS (50 %) and total vessel occlusion. Time-dependent fluorescence intensity curves were recorded by FCI. Slope of fluorescence intensity (SFI) and background-subtracted peak fluorescence (BSFI) intensity were calculated and data compared to myocardial blood flow measurements using FM. All NFLS and FLS reduced myocardial perfusion as quantified by FCI showing decreased normalized BSFI and SFI (P < 0.001). Box-plot analysis showed significant difference between NFLS (50 and 90 %) and FLS (50 %) assessed by BSFI (P < 0.001) and SFI (P < 0.001). In each animal, a linear correlation between FM-derived myocardial blood flow and FCI-derived BSFI (r = 0.936, P < 0.001) or SFI (r = 0.942, P < 0.001) was observed during baseline, hyperemia, graded NFLS, and FLS. Both, BSFI (r = 0.789, P < 0.001) and SFI (r = 0.802, P < 0.001) significantly correlated with transit-time flow measurements. FCI quantitative technology is capable of distinguishing between non-ischemia inducing NFLS and ischemia inducing FLS showing a good correlation compared to fluorescent microspheres.

Theoretical Examination of Long-Range Energy Propagation in Nano-Engineered Light-Harvesting Antenna Arrays

Excitation energy transport in a biomimetic molecular nanoarray constructed from LH2 antenna complexes is investigated by a master equation approach including the effect of coherent hopping. Calculated stationary and transient fluorescence signals upon incidence of a diffraction-limited light pulse are compared with measurements. Energy transport was established from the influence of active energy-guiding layers on the observed fluorescence emission. Energy migration occurs as a result of efficient coupling between many hundreds of LH2 complexes. We obtain an analytical expression of stationary fluorescence distribution solving the master equations of the system. The time-dependent fluorescence intensity is derived using the same formalism. The numerical results show a reasonable consistency with the experimental result in the engineered nanoarray of LH2 complexes. In addition, our results show that quantum coherence mechanism is necessary to explain the long distance energy transport. These results demon...

A detailed approach to study the antibacterial mechanisms of nanostructure

To overcome the limitations of the conventional inhibition method for mechanism study, here we developed a combined CLSM technique as an alternative approach to evaluate and explain the antibacterial process of nanostructure at single cell level. Three different nanostructures (dumbbell-shaped ZnO, rod-shaped ZnO and ZnO/Ag composites) were examined here as a model system. Their antibacterial processes against Escherichia coli (E. coli) were quantitatively studied in detail. According to the obtained time-dependent mean fluorescence intensity (MFI) decay dynamics, an interesting two-step cellular disruption process was observed and discussed for the first time. The combined CLSM technique described here is superior to standard growth method for they can provide a more detailed and reliable description of cell–nanostructure interactions.

Sensitive and fast recognition of explosives using fluorescent polymer sensors and pattern recognition analysis

An optical sensor array consisting four fluorescent polymer thin films was investigated to recognize nitro containing explosive, TNT (2,4,6-trinitro toluene) and its simulants. The fluorescence quenching behaviour in presence of these analyte vapors was measured at peak emission of fluorescent materials upon excitation at 440 nm under ambient conditions. The time-dependence of fluorescence intensity for each polymer was obtained in presence of the analyte vapors. Feature patterns, like fluorescence quenching percentage at a certain time, were extracted from the time-dependent fluorescence intensity curve and were used as the input for pattern recognition tools. Even though the explosives were not distinguishable by principle component analysis (PCA) in 2 s, support vector machine (SVM) neural network showed 90% recognition rate. However, the recognition rate of SVM neural network was improved to 100% in 5 s whereas the fuzzy ARTMAP network had a perfect recognition rate in 6 s. Furthermore, the developed recognition system showed robustness to additive noise and can detect and discriminate between simulants and the explosive TNT within 10 s at sub parts per billion (ppb) level.

Sequential ordering among multicolor fluorophores for protein labeling facility via aggregation-elimination based β-lactam probes

Development of protein labeling techniques with small molecules is enthralling because this method brings promises for triumph over the limitations of fluorescent proteins in live cell imaging. This technology deals with the functionalization of proteins with small molecules and is anticipated to facilitate the expansion of various protein assay methods. A new straightforward aggregation and elimination-based technique for a protein labeling system has been developed with a versatile emissive range of fluorophores. These fluorophores have been applied to show their efficiency for protein labeling by exploiting the same basic principle. A genetically modified version of class A type β-lactamase has been used as the tag protein (BL-tag). The strength of the aggregation interaction between a fluorophore and a quencher plays a governing role in the elimination step of the quencher from the probes, which ultimately controls the swiftness of the protein labeling strategy. Modulation in the elimination process can be accomplished by the variation in the nature of the fluorophore. This diversity facilitates the study of the competitive binding order among the synthesized probes toward the BL-tag labeling method. An aggregation and elimination-based BL-tag technique has been explored to develop an order of color labeling from the equimolar mixture of the labeling probe in solutions. The qualitative and quantitative determination of ordering within the probes toward labeling studies has been executed through SDS-PAGE and time-dependent fluorescence intensity enhancement measurements, respectively. The desirable multiple-wavelength fluorescence labeling probes for the BL-tag technology have been developed and demonstrate broad applicability of this labeling technology to live cell imaging with coumarin and fluorescein derivatives by using confocal microscopy.

Study of the Effect of Ultraviolet Exposure on Bio-oil by Laser-Induced Fluorescence Spectroscopy

Laser-induced fluorescence was used to simulate and monitor the effect of ultraviolet (UV) exposure on the chemical stability of bio-oil. Bio-oil obtained from fast pyrolysis of biomass has potential for replacing fossil fuel in the future as liquid fuels. Pyrolysis-derived bio-oil contains up to 400 chemical compounds and tends to be very unstable, both physically and chemically. Bio-oil produced from four different sources (pine lumber, pine bark, oak bark, and oak wood) was used in this study. Synthetic bio-oil composed of 10 chemicals but having a similar weight percentage (wt %) of compound groups and having a similar spectroscopic property as bio-oil was prepared. Synthetic bio-oil simplifies the limitation in the study posed by complex chemical composition in bio-oil. It was concluded that phenols present in the bio-oil show chemical instability by giving time-dependent fluorescence intensity.

Conjugated Polyelectrolyte Based Fluorescence Turn-On Assay for Real-Time Monitoring of Protease Activity

A fluorescence "turn-on" assay for monitoring protease activity is developed on the basis of a water-soluble carboxylated polyfluorene derivative, PFP-CO₂Na, and its different fluorescence response toward cytochrome c (cyt c) and its fragments. PFP-CO₂Na is synthesized via Suzuki coupling polymerization between 2,7-dibromo-9,9-bis(3'-tert-butyl propanoate)fluorene and 1,4-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-benzene, followed by treatment with trifluoroacetic acid and Na₂CO₃. The fluorescence of PFP-CO₂Na can be significantly quenched by cyt c due to complexation-mediated electron transfer between the polymer and protein. Using the complex of PFP-CO₂Na/cyt c as a substrate, a real-time fluorescence turn-on assay for trypsin activity study has been developed. Addition of trypsin to the substrate solution induces gradual recovery of the fluorescence intensity for PFP-CO₂Na due to trypsin-catalyzed hydrolysis of cyt c, which dissociates the heme moiety from the polymer vicinity. The time-dependent fluorescence intensity increase of PFP-CO₂Na in the presence of trypsin allows us to derive the initial reaction rates and k(cat)/K(m) (5350 M⁻¹ s⁻¹) for trypsin-catalyzed hydrolysis. Addition of trypsin inhibitor efficiently inhibits trypsin-catalyzed hydrolysis reaction of cyt c, which leads to a decreased fluorescence turn-on response of PFP-CO₂Na.

Single-Cell Transfection by Electroporation Using an Electrolyte/Plasmid-Filled Capillary

Single-cell transfection of adherent cells has been accomplished using single-cell electroporation (SCEP) with a pulled capillary. HEPES-buffered physiological saline solution containing pEGFP plasmid at a low concentration (0.16 approximately 0.78 microg/microL) filled a 15 cm long capillary with a tip opening of 2 microm. The electric field is applied to individual cells by bringing the tip close to the cell and subsequently applying one or two brief electric pulses. Many individual cells can thus be transfected with a small volume of plasmid-containing solution (approximately 1 microL). The extent of electroporation is determined by measuring the percentage loss of freely diffusing thiols (chiefly reduced glutathione) that have been derivatized with the fluorogenic ThioGlo 1. A mass transport model is used to fit the time-dependent fluorescence intensity decay in the target cells. The fits, which are excellent, yield the electroporation-induced fluorescence loss at steady state and the mass transfer rate through the electroporated cell membrane. Steady-state fluorescence loss ranged approximately from 0 to about 80% (based on the fluorescence intensity before electroporation). For the cells having a loss of thiol-ThioGlo 1 fluorescence intensity greater than 10% and mass transfer rate greater than 0.03 s(-1), EGFP fluorescence is observed after 24 h. The EGFP fluorescence is increased at 48 h. With a loss smaller than 10% and a mass transfer rate smaller than 0.03 s(-1), no EGFP fluorescence is detected. Thus, transfection success is closely related to the small molecule mass transport dynamics as indicated by the loss of fluorescence from thiol-ThioGlo 1 conjugates. The EGFP expression is weaker than bulk lipid-mediated transfection, as indicated by the EGFP fluorescence intensities. However, the success with the single-cell approach is considerably greater than lipid-mediated transfection.

Conjugated Polyelectrolyte-Based Real-Time Fluorescence Assay for Alkaline Phosphatase with Pyrophosphate as Substrate

The fluorescence of the anionic, carboxylate-substituted poly(phenylene ethynylene) polymer PPECO2 is quenched very efficiently via the addition of 1 equiv of Cu(2+). Addition of pyrophosphate (PPi) into the weakly fluorescent solution of PPECO2 and Cu(2+) induces recovery of the polymer's fluorescence; the recovery occurs because PPi complexes with Cu(2+), effectively sequestering the ion so it cannot bind to the carboxylate groups of the polymer. A calibration curve was developed that relates the extent of fluorescence recovery to [PPi], making the PPECO2-Cu(2+) system a sensitive and selective turn-on sensor for PPi. Using the PPECO2-Cu(2+) system as the signal transducer, a real-time fluorescence turn-off assay for the enzyme alkaline phosphatase (ALP) using PPi as the substrate is developed. The assay operates with [PPi] in the micromolar range, and it offers a straightforward and rapid detection of ALP activity with the enzyme present in the nanomolar concentration range, operating either in an end point or real-time format. Kinetic and product inhibition parameters are derived by converting time-dependent fluorescence intensity into PPi (substrate) concentration, thus allowing calculation of the initial reaction rates (v(o)). Weak, nonspecific fluorescence responses are observed concomitant to addition of other proteins to the assay solution; however, the signal response to ALP is demonstrated to arise from the ALP catalyzed hydrolysis of PPi to phosphate (Pi).

Structural Kinetics of Cardiac Troponin C Mutants Linked to Familial Hypertrophic and Dilated Cardiomyopathy in Troponin Complexes

The key events in regulating cardiac muscle contraction involve Ca(2+) binding to and release from cTnC (troponin C) and structural changes in cTnC and other thin filament proteins triggered by Ca(2+) movement. Single mutations L29Q and G159D in human cTnC have been reported to associate with familial hypertrophic and dilated cardiomyopathy, respectively. We have examined the effects of these individual mutations on structural transitions in the regulatory N-domain of cTnC triggered by Ca(2+) binding and dissociation. This study was carried out with a double mutant or triple mutants of cTnC, reconstituted into troponin with tryptophanless cTnI and cTnT. The double mutant, cTnC(L12W/N51C) labeled with 1,5-IAEDANS at Cys-51, served as a control to monitor Ca(2+)-induced opening and closing of the N-domain by Förster resonance energy transfer (FRET). The triple mutants contained both L12W and N51C labeled with 1,5-IAEDANS, and either L29Q or G159D. Both mutations had minimal effects on the equilibrium distance between Trp-12 and Cys-51-AEDANS in the absence or presence of bound Ca(2+). L29Q had no effect on the closing rate of the N-domain triggered by release of Ca(2+), but reduced the Ca(2+)-induced opening rate. G159D reduced both the closing and opening rates. Previous results showed that the closing rate of cTnC N-domain triggered by Ca(2+) dissociation was substantially enhanced by PKA phosphorylation of cTnI. This rate enhancement was abolished by L29Q or G159D. These mutations alter the kinetics of structural transitions in the regulatory N-domain of cTnC that are involved in either activation (L29Q) or deactivation (G159D). Both mutations appear to be antagonistic toward phosphorylation signaling between cTnI and cTnC.

Evolutional Design of a Hyperactive Cysteine- and Methionine-free Mutant of Escherichia coli Dihydrofolate Reductase

We developed a strategy for finding out the adapted variants of enzymes, and we applied it to an enzyme, dihydrofolate reductase (DHFR), in terms of its catalytic activity so that we successfully obtained several hyperactive cysteine- and methionine-free variants of DHFR in which all five methionyl and two cysteinyl residues were replaced by other amino acid residues. Among them, a variant (M1A/M16N/M20L/M42Y/C85A/M92F/C152S), named as ANLYF, has an approximately seven times higher k(cat) value than wild type DHFR. Enzyme kinetics and crystal structures of the variant were investigated for elucidating the mechanism of the hyperactivity. Steady-state and transient binding kinetics of the variant indicated that the kinetic scheme of the catalytic cycle of ANLYF was essentially the same as that of wild type, showing that the hyperactivity was brought about by an increase of the dissociation rate constants of tetrahydrofolate from the enzyme-NADPH-tetrahydrofolate ternary complex. The crystal structure of the variant, solved and refined to an R factor of 0.205 at 1.9-angstroms resolution, indicated that an increased structural flexibility of the variant and an increased size of the N-(p-aminobenzoyl)-L-glutamate binding cleft induced the increase of the dissociation constant. This was consistent with a large compressibility (volume fluctuation) of the variant. A comparison of folding kinetics between wild type and the variant showed that the folding of these two enzymes was similar to each other, suggesting that the activity enhancement of the enzyme can be attained without drastic changes of the folding mechanism.

Real-time Enzyme Dynamics Illustrated with Fluorescence Spectroscopy of p-Hydroxybenzoate Hydroxylase

We have used the flavoenzyme p-hydroxybenzoate hydroxylase (PHBH) to illustrate that a strongly fluorescent donor label can communicate with the flavin via single-pair Förster resonance energy transfer (spFRET). The accessible Cys-116 of PHBH was labeled with two different fluorescent maleimides with full preservation of enzymatic activity. One of these labels shows overlap between its fluorescence spectrum and the absorption spectrum of the FAD prosthetic group in the oxidized state, while the other fluorescent probe does not have this spectral overlap. The spectral overlap strongly diminished when the flavin becomes reduced during catalysis. The donor fluorescence properties can then be used as a sensitive antenna for the flavin redox state. Time-resolved fluorescence experiments on ensembles of labeled PHBH molecules were carried out in the absence and presence of enzymatic turnover. Distinct changes in fluorescence decays of spFRET-active PHBH can be observed when the enzyme is performing catalysis using both substrates p-hydroxybenzoate and NADPH. Single-molecule fluorescence correlation spectroscopy on spFRET-active PHBH showed the presence of a relaxation process (relaxation time of 23 micros) that is related to catalysis. In addition, in both labeled PHBH preparations the number of enzyme molecules reversibly increased during enzymatic turnover indicating that the dimer-monomer equilibrium is affected.

Measurements and calculations of metastable level lifetimes inFeX,FeXI,FeXII,FeXIII,andFeXIV

Lifetimes of metastable levels in the ground term of Fe ions within the ${3s}^{2}{3p}^{k},k=1\char21{}5,$ isoelectronic sequences have been measured. These measurements were performed utilizing ions that were selected by mass to charge ratio while transported from an electron cyclotron resonance ion source to a Kingdon ion trap, where they were captured and then confined for periods of up to 2.1 s. During this storage period, selected emission wavelengths of transitions from metastable levels in the visible or near-ultraviolet spectral regions were isolated using interference filters, and the time-dependent fluorescence intensities were measured using a photomultiplier tube. Measurement precisions on the order of 2% were achieved in favorable cases. The measured lifetimes are $\ensuremath{\tau}(\mathrm{Fe}X,{3s}^{2}{p}^{5}{}^{2}{P}_{1/2})=13.64\ifmmode\pm\else\textpm\fi{}0.25\mathrm{ms},$ $\ensuremath{\tau}(\mathrm{Fe}\mathrm{XI},{3s}^{2}{3p}^{4}{}^{1}{D}_{2})=9.86\ifmmode\pm\else\textpm\fi{}0.22\mathrm{ms},$ $\ensuremath{\tau}(\mathrm{Fe}\mathrm{XII}{,3s}^{2}{3p}^{3}{}^{2}{P}_{3/2})=1.85\ifmmode\pm\else\textpm\fi{}0.24\mathrm{ms},$ $\ensuremath{\tau}(\mathrm{Fe}\mathrm{XII},{3s}^{2}{3p}^{3}{}^{2}{P}_{1/2})=4.38\ifmmode\pm\else\textpm\fi{}0.42\mathrm{ms},$ $\ensuremath{\tau}(\mathrm{Fe}\mathrm{XII},{3s}^{2}{3p}^{3}{}^{2}{D}_{3/2})=20.35\ifmmode\pm\else\textpm\fi{}1.24\mathrm{ms},$ $\ensuremath{\tau}(\mathrm{Fe}\mathrm{XIII},{3s}^{2}{3p}^{2}{}^{1}{D}_{2})=6.93\ifmmode\pm\else\textpm\fi{}0.18\mathrm{ms},$ and $\ensuremath{\tau}(\mathrm{Fe}\mathrm{XIV},{3s}^{2}3p{}^{2}{P}_{3/2})=17.52\ifmmode\pm\else\textpm\fi{}0.29\mathrm{ms}.$ These results are compared with existing and with new theoretical calculations, which have estimated uncertainties on the order of $10\char21{}25%.$

Collisional quenching of the H(n = 3) atomsby molecular hydrogen: cross section measurements

The H(3l) + H2 collision has been investigated in thevelocity range of 2-7 km s-1, at room temperature,through time-dependent fluorescence intensity measurementsafter pulsed excitation, at different pressures; thel-mixing cross sections and the cross sections for non-radiativequenching processes have been determined.