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UV-assisted advanced oxidation processes (AOPs) are promising for the removal of microcystin-LR (MC-LR), one of cyanotoxins released during harmful algal blooms. Nevertheless, the efficiency and potential of the photo-Fenton-like process (UV-C/Fe(III)/H2O2) in treating MC-LR have not been explored in much detail. In this study, MC-LR degradation efficiencies of various UV-assisted AOPs were compared that they were higher in the order: UV-C/Fe(III)/H2O2 > UV-C/Fe(II)/H2O2 > UV-A/TiO2 > UV-C/H2O2 > UV-C > UV-A/Fe(II)/H2O2 > UV-A/H2O2 > UV-A. The concentrations of Fe(III) and H2O2 used in the photo-Fenton-like process were varied to evaluate their influences on MC-LR degradation in both deionized water and a water sample from Nak-Dong River, Daegu (South Korea). The highest removal efficiency (>80%) for MC-LR was achieved after 15 min by the photo-Fenton process at a low optimum Fenton reagent concentration (Fe = 0.5 mg L−1 and H2O2 = 1 mg L−1) in the river water. Twelve transformation products of MC-LR were identified with 1029.5, 1012.5, 1015.5, 1011.5, 965.6, 835.5, 815.4 and 783.4 m/z (two products) with the presence of four reaction sites: the conjugated diene bond of Adda, the methoxy group of Adda, the C C bond of Mdha, and the acid group of MeAsP. Theses alleviated the hepatotoxicity of MC-LR, as indicated by a protein phosphatase (PP) 2A assay. Considering the impacts of the chemistry for the treatment of river water, natural organic matter has a slightly higher impact on MC-LR degradation than the initial pH and alkalinity. The kMC-LR were maintained at 0.167–0.187 min−1 and t1/2 (min), obtained from the different river water samples, were all within 5 min in spite of the relatively high dissolved organic carbon concentrations.

The nonadiabatic coupling terms (NACTs, Fij’s) between triplet electronic states can be well approximated with a very simple equation suggested recently [J. Chem. Phys. 146, 064107 (2017)], using only adiabatic potential energies ( V i a and V j a ). Furthermore, the second-order differentiation can be evaluated accurately from the energy gaps, ( V i a - V j a ) , at just three consecutive geometries, even at a point exhibiting severe singularity in the behaviour of NACTs. The performance of this approximation method was investigated for the couplings between the 3 3 Π and 4 3 Π states of NaK, between the 1 3 B 3 u and 2 3 B 3 u states of N2, and between the 2 3 A ″ and 3 3 A ″ states of methylene (CH2).

Recent discoveries of alkali metal structures with novel properties at high pressures have stimulated considerable interest in binary mixtures of these metals under compression. This work reports a broad investigation of the physical and chemical behaviors of different Na–K stoichiometries by first-principles calculations and swarm-intelligence structure searching methodology. In addition to five structures previously proposed, seven new structures with stoichiometries of NaK, NaK2, and NaK3 were uncovered. New NaK2 compounds with Pm and Pnma structures are potential superconductors with Tc of 12.17 K at 250 GPa and 6.26 K at 400 GPa, respectively. The NaK and NaK3 compounds show intriguing decomposition–recombination behavior. The newly found Cmcm structure of NaK, Pm structure of NaK2, and Pmmm and Cmcm structures of NaK3 are electrides with strong interstitial electron localization. What's more, interesting reversible charge transfer between Na and K occurred as the pressure increased. Our discoveries prove that pressure is a powerful tool for creating new exotic materials in the binary alkali compounds.

Urban particles were investigated using a single particle aerosol mass spectrometer (SPAMS) in Chongqing during the summertime (from 07/05/2014 to 08/06/2014). Chemical composition, mixing state, and atmospheric behavior of urban particles were studied. The major particle types include ECOC (Elemental-Carbon-Organic-Carbon 20.6%), OC (20.1%), KSec (K-Secondary) (13.3%), BB (Biomass burning, 11.9%), NaK (sodium-potassium-rich, 7.3%), Al-rich (4.0%), Fe-rich (3.2%), Ca-rich (1.4%), Ca-EC (1.6%), and NaKPb (0.5%). EC, ECOC, OC, and Ca-EC were prevalent in the condensation mode ( Fe-rich > EC > Ca-EC > Ca-rich > KSec > OC > NaK > ECOC > Al-rich > BB. Increased number fraction of EC and KSec were correlated with the increase of odd oxygen (O x = O 3 + NO 2 ). EC, OC, and ECOC were enriched at higher relative humidity. The findings of this study on the mixing state, temporal variation, processing, and evolution of single particles provide new insight into the atmospheric behavior and impacts of urban particles.

One of the main challenges using biofuels, such as pellets or wood chips in domestic boilers, is the slagging and fouling risks associated to the process, which could damage the boiler and limit its efficiency. The prediction of sintering and slagging in biomass combustion is essential to establish biofuel quality standards, and minimize their harmful effects. In this work, we analysed the chemical composition of 40 woodchips samples from different genera and origins in order to predict slagging. We studied two indexes of deposition (%B and the NaK/B) in order to limit sintering of biomass ashes. In addition, a new threshold classification was proposed for ratio-slag viscosity index. These indexes were validated with two different tests: a qualitative test, and a quantitative test (Bioslag). Our results showed that the species chosen did not have an impact in slagging and sintering. However, biomass with high concentrations of SiO2 and tree bark showed high risk of slagging. On the other hand, high CaO concentrations showed a low slagging risk. The results obtained from the validation tests showed similar results to the ones obtained from the indexes. It can be concluded that the %B and NaK/B indexes show good potential and should be considered as tools for predicting slagging in woody and herbaceous biomass.

During the Engineering Validation and Engineering Design Activities (EVEDA) phase (2007-2014) of the International Fusion Materials Irradiation Facility (IFMIF), an advanced engineering design of the High Flux Test Module (HFTM) has been developed with the objective to facilitate the controlled irradiation of steel samples in the high flux area directly behind the IFMIF neutron source. The development process addressed included manufacturing techniques, CAD, neutronic, thermal-hydraulic and mechanical analyses complemented by a series of validation activities. Validation included manufacturing of 1:1 parts and mockups, test of prototypes in the FLEX and HELOKA-LP helium loops of KIT for verification of the thermal and mechanical properties, and irradiation of specimen filled capsule prototypes in the BR2 test reactor. The prototyping activities were backed by several R&D studies addressing focused issues like handling of liquid NaK (as filling medium) and insertion of Small Specimen Test Technique (SSTT) specimens into the irradiation capsules. This paper provides an up-todate design description of the HFTM irradiation device, and reports on the achieved performance criteria related to the requirements. Results of the validation activities are accounted for and the most important issues for further development are identified.

The double cation borohydrides NaK(BH 4 ) 2 has a total H 2 content of 8.8 wt.% and has suggested as a potential candidate for hydrogen storage applications. The four decomposition reaction paths associated with NaK(BH 4 ) 2 are predicted to reaction thermodynamics for hydrogen release within the temperature range of 21–126 °C. However, a critical drawback with first-principles is that the predicted reaction mechanism might not be the most stable reaction path. The aim of this study is to provide an answer to this problem by examining possible metastable paths for four reactant mixtures whose reaction mechanisms were previously predicted using first principles thermodynamics calculations.

The relative transition dipole moment function M(R) for the 4 3 R + ? a 3 R + electronic transition in the

Expressed protein ligation (EPL) is a semisynthetic technique for the chemoselective ligation of a synthetic peptide to a recombinant peptide that results in a native peptide bond at the ligation site. EPL therefore allows us to engineer proteins with chemically defined, site-specific modifications. While EPL has been used mainly in investigations of soluble proteins, in recent years it has been increasingly used in investigations of integral membrane proteins. These include studies on the KcsA K(+) channel, the non-selective cation channel NaK, and the porin OmpF. These studies are discussed in this review.

The Na + and K + channels are essential to neural signaling, but our current knowledge at the atomic level is mainly limited to the conducting mechanism of K + . Unlike a K + channel having four equivalent K + -binding sites in its selectivity filter, a NaK channel has a vestibule in the middle part of its selectivity filter, and can conduct both Na + and K + ions. However, the underlying mechanism for non-selective ion conduction in NaK remains elusive. Here we find four small grottos connecting with the vestibule of the NaK selectivity filter, which form a vestibule-grotto complex perpendicular to the filter pore with a few water molecules within it. It is shown that two or more of the water molecules coming to the vestibule to coordinate the cation are necessary for conducting both Na + and K + ions, while only one water molecule in the vestibule will obstruct ion permeation. Thus, the complex with the aid of interior water movement forms a dynamic hydration valve which is flexible in conveying different cations through the vestibule. Similar exquisite hydration valve mechanisms are expected to be utilized by other non-selective cation channels, and the results should shed new light on the importance of water in neural signaling.

A parameter-free analytical formula for dissociation energies of diatomic molecules is proposed by Fan and Sun (2009) [20] based on LeRoy and Bernstein's vibrational energy expression near dissociation limit. Using three highest vibrational energies which may be generated by the algebraic method (AM) presented in our previous study and by some other physical methods, the new formula is applied to study the molecular dissociation energies of 10 electronic states of KH, (7)LiD, (7)LiH, (6)LiH, NaK, NaLI and NaRb heteronuclear diatomic molecules which have regular (Morse-like) potentials in this work. The results show that the AM energies E(upsilon)(AM) and dissociation energies D(e)(AM) have excellent agreement with experimental values.

How K(+) channels are able to conduct certain cations yet not others remains an important but unresolved question. The recent elucidation of the structure of NaK, an ion channel that conducts both Na(+) and K(+) ions, offers an opportunity to test the various hypotheses that have been put forward to explain the selectivity of K(+) ion channels. We test the snug-fit, field-strength, and over-coordination hypotheses by comparing their predictions to the results of classical molecular dynamics simulations of the K(+) selective channel KcsA and the less selective channel NaK embedded in lipid bilayers. Our results are incompatible with the so-called strong variant of the snug-fit hypothesis but are consistent with the over-coordination hypothesis and neither confirm nor refute the field-strength hypothesis. We also find that the ions and waters in the NaK selectivity filter unexpectedly move to a new conformation in seven K(+) simulations: the two K(+) ions rapidly move from site S4 to S2 and from the cavity to S4. At the same time, the selectivity filter narrows around sites S1 and S2 and the carbonyl oxygen atoms rotate 20 degrees -40 degrees inwards toward the ion. These motions diminish the large structural differences between the crystallographic structures of the selectivity filters of NaK and KcsA and appear to allow the binding of ions to S2 of NaK at physiological temperature.

The total resistivity for the NaK, NaRb and NaCs alkali alloys was divided into partial resistivities and calculated by means of Zimans’s formula within a simplified and semi-empirical approach. It is shown that the height of the parabolic resistivity behavior versus concentration is related to the scattering potential whereas the position of the maximum depends on the structure of liquid. Further it appears clearly that the leading contribution is due to the sodium as a result of its muffin tin zero enhancement with respect to its value in the pure liquid phase.

The polarization labeling spectroscopy technique is used to study the 6 1 Π ←X 1 Σ + and 7 1 Π ←X 1 Σ + band systems of the NaK molecule located in the UV range. For both excited states accurate molecular constants are derived which describe the 6 1 Π state to 68% and the 7 1 Π state to 71% of their potential well depths. The parameters deduced from the experiment are compared with the recent theoretical calculations.

The 4 1 Σ + state of NaK molecule has been observed for the first time and studied by polarisation labelling spectroscopy technique. A total of 1567 rovibronic levels in this state were measured with an accuracy better than 0.1 cm −1 . The inverted perturbation approach method was used to construct the potential energy curve of the 4 1 Σ + state. The irregular shape of the potential confirms earlier theoretical predictions.

Polarization labelling spectroscopy is applied to study the previously unobserved 5 1 Σ + state of the NaK molecule. Molecular constants and a Rydberg–Klein–Rees (RKR) potential energy curve based on these constants are determined. The values of Te, ωe and Re are 23530.62(6) cm−1, 115.60(6) cm−1 and 4.307 A, respectively.

Recent experimental works have been devoted to the spectroscopy of highly excited states of NaK, confirming the accuracy of our previous calculations [S. Magnier and Ph. Millie, Phys. Rev. A: Gen. Phys. 54, 204 (1996)] of spectroscopic constants and potential curves. Among them, [E. Laub, I. Mazsa, S. C. Webb, J. La Civita, I. Prodan, Z. J. Zabbour, R. K. Namiotka, and J. Huennekens, J. Mol. Spectrosc. 193, 376 (1999)] have deduced from their measurements the variation of the transition dipole moment with the interatomic distance for the transition X(1)Sigma+ --> (3)(1)Pi. They have shown that a large discrepancy was observed with the previous ab initio calculations currently used as a guide for spectroscopic experiments. Upon request of several experimentalists, we have computed again potential curves for electronic states correlated up to Na(4p) + K(4s) as well as relevant permanent and transition dipole moments. We present extensive predictions for the electronic structure of NaK (potential energies, dipole moments) for which numerical data have been listed in a data base available as supplementary data. Copyright 2000 Academic Press.

The 41Π and 51Π states of the NaK molecule have been investigated experimentally by polarization labelling spectroscopy technique and theoretically within the framework of the ab initio pseudopotential method. A very good agreement has been obtained between the calculated potential curves and those determined from experimental observations.

We have proposed an error resilient video coding system, which dynamically replaces reference pictures in inter-frame coding according to the backward channel signaling. This system can prevent the temporal error propagation, because the encoder would not use the erred picture as the reference picture. This system has two modes, one is ACK mode and the other is NACK mode. ACK mode is effective in more erroneous condition, and NACK mode is effective in less erroneous condition. In this paper, we explain both modes and focus on the mode switching mechanism according to the error condition on the network so that the optimal performance can be achieved in any error conditions by the proposed system. We show the performance of our proposed system compared with the previous version of ITU-T H.263, which did not have a reference picture selection mode, by a computer simulation as well.

This article reports the observation of the molecular fluorescence circularity under irradiation with linearly polarised light. This alignment-orientation conversion phenomenon arises as a result of partial transformation from alignment of the ensemble of 1 P state molecular angular momenta into their orientation under the effect of non-linear dc Stark effect. Circularity rate up to 0.12 was observed in D 1 P! X 1 S fluorescence of 23 Na 39 K molecules in agreement with the theoretically predicted value.

A combined experimental and theoretical study of the vibrational wave packet dynamics for the NaK molecule in the A (1)Sigma(+) state is presented. The experiment utilises a 790 nm one-colour fem ...

The Haystack radar has been observing the orbital debris environment since October 1990. These measurements have provided orbital debris researchers with two important tools for characterizing the environment: 1) the ability to detect small size debris objects from previously unknown sources and 2) the ability to extend the size distribution from the catalog limit (≈10 cm) down to 0.5 cm. Haystack data has identified small debris from several breakups and anomalous events: the Pegasus upper stage, satellite 23106; Cosmos 1484, satellite 14207; COBE, satellite 20332; Meteor 2–16 rocket body, satellite 18313; and the leakage of NaK droplets from the RORSAT class satellites. The time history of detection rate, and the flux, altitude, inclination, and size distributions have shown that the environment is very dynamic and the data is extremely useful as a benchmark for orbital debris modeling.

In its current 1997 release version the MASTER space debris model considers orbital fragmentations to be the main source for the generation of space debris, while other sources are not taken into account. For this reason, the actual reference population is dominated by particles originating from 127 historical fragmentation events, mainly explosions. Since these explosion fragments can not account for aluminum oxide particles or paint materials identified in the course of the chemical analysis of impact crater residuals, MASTER currently is upgraded to cover additional source terms in its population generation module. Besides micro debris sources like surface degradation or impact ejecta, generation mechanisms for larger scale particles like NaK droplets will be considered in the next MASTER release. Additionally, orbital firings of Solid Rocket Motors (SRMs) as a contributor to both size regimes are planned to be included. To implement all these additional source terms, a variety of sub-models reflecting the generation processes had to be derived. In this context, the diversity of Al2O3 dust and slag objects exhausted from SRM burns in terms of basic generation characteristics as well as in orbital dynamics of the particle cloud has been reviewed and results documenting the influence of this source on the debris environment are presented.

Laser-induced fluorescence (LIF) optical spectra of the D1Pi-X1Sigma+ system of the NaK molecule have been reinvestigated. In this new analysis, quantum numbers have been assigned to 3000 selected fluorescence lines for a wide range of vibrational and rotational levels (J

We present new improved equations for three still widely used NaK, NaLi and SiO2 geothermometers (obtained by statistical treatment of the data and application of outlier detection and rejection as well as theory of error propagation) and compare them with those by Fournier and others. New equations are also developed for estimating errors associated with the use of these new geothermometric equations and comparing them with the performance of the original equations. The errors in the use of the new NaK equation for temperatures ranging from 80 to 350 °C vary from about 19 to 34%, which is lower than the corresponding errors (24–43%) for the original Fournier equation. Similarly, for temperatures ranging from about 50 to 320 °C, our new equation for NaLi geothermometer for Cl < 0.3 m shows errors of about 13–34% as compared to 15–39% for the original equation, and for Cl ≥ 0.3 m, from 10 to 44%, much lower than 26–106% estimated for the corresponding original equation. Finally, for temperatures ranging from 20 to 210 °C our results show that the total propagated errors of the new geothermometric equation for SiO2 < 295 ppm are about 1–9%, smaller than 3–12% for the original SiO2 geothermometer. We have proposed a linear equation for the temperature range of 210 to 310 °C (SiO2 ≥ 295 ppm), which shows considerably smaller total propagated errors (2–3%) than for the original equation (5–29%).

We report here the application of optical-radio frequency double resonance spectroscopy for individual rotational levels of the NaK D 1 Π state. Lambda doubling constant q values for five ν′, J ′ levels are obtained. These data are combined with measurements of dc e - f Stark-mixing-induced changes in optical spectra, and the electric dipole moment d p in the D 1 Π state is determined.

The real-time vibrational dynamics of NaK molecules excited to the electronic A1∑+ state has been studied isotipe-selectively by means of time-resolved three-photon ionization. For 23Na39K and 23Na41K vibrational periods of T A (23,39) ≊ 441 fs and T A (23,41) ≊446 fs are determined. A detailed Fourier analysis proofs a weak perturbation of the wave packet caused by spin-orbit coupling of A and b3ν states. Pronounced fractional revivals of the fundamental oscillation occur at T frev 1,2(23,39) ≊ 75 ps and T frev 1,2(23,41) ≊ 68 ps . Spectrograms of the real-time data nicely reveal a strong fractional revival at T frev 1,4 = 1 2 T frev 1,2 . Further revivals of weaker intensity at Tfrev1,6(23,39) ≈ 25 ps and Tfrev1,3(23,39) ≈ 50 ps are found for the lighter isotope.

This paper considers the following selective-repeat ARQ (automatic-repeat-request) policy which is mainly used in a data communication system: We transmit a block of data successively to a receiver. A negative (NAK) or positive (ACK) acknowledgement is returned from a receiver, depending on whether errors of data have occurred or not. When we have received NAK, we retransmit the erroneous block, otherwise we continue to send new blocks waiting for transmission. The expected numbers of ACK's and retransmitted blocks and the mean time until the first successive N + 1 NAK's are derived. Using these results, the optimal numbers N ∗ which minimize the mean time per successful blocks and the mean loss time in the mean time are discussed.

The approximate sum rule ≈ Σv2 (Ev1 - Ev2)n, where f, g are operators which couple the vibrational levels v1, v2 of two interacting electronic states and ΔU=U1—U2 is the difference of the corresponding internuclear potentials, is numerically tested for radiative lifetimes, electronic polarizabilities, fine-structure constants and Lande factors for the vibronic states of the NaK molecule. The approximation is demonstrated to have high accuracy and efficiency for non-diagonal systems, especially for those with significant continuum contributions. Simple ways of estimating the sum rule accuracy are given.

Tritium recovery by cold trapping in an intermediate NaK loop is considered for a self-cooled Pb-17Li blanket. The transient build-up of tritium inventory in the Pb-17Li and NaK loops is calculated for a test-plug to be used in NET. A steady-state tritium inventory of about two gramms is assessed for the blanket system including the cold traps. Hydrogen separation and release experiments in cold traps are going to start. Calculations of the temperature, velocity and concentration distributions in cold traps point to the influence of natural convection in mesh packed cold traps. First hydrogen release experiments were performed with hydride powder and hydride crystals. Different release mechanisms were observed during recovery from NaK which suggest that tritium recovery from drained cold traps should be preferred.

A stimulated red emission is studied by hybrid transitions involving the NaK heteronuclear molecule. The excitation channels in NaK and K are identified and the mechanisms of the stimulated emission are discussed.

Today a country's economic viability and its citizens’ job mobility require that its workforce have a strong micro- and nanotechnology education providing a skill set covering synthesis, fabrication, and characterization. An international model is offered for creating such a skilled workforce which is based on a resource sharing approach between research universities and technical colleges. For the good of a country and its citizens, workers must have the educational background that allows them to move from job to job as sectors wax and wane. This broad twenty-first century education that is proposed provides the infrastructure that is needed to accomplish this and to thereby give a country the intellectual capital to be a competitive force on the rapidly changing world manufacturing scene.

Five systems of the D 1Π-a3∑+ transition of NaK molecules, assigned as α, β,γ, δ and ϵ are observed with various single mode 4765 A argon ion laser line excitations Among them, only system α had been reported and analyzed previously. The headsof these systems are at 15978, 16610, 16857, 16914 and 16671 cm-1, respectively The estimated upper and lower vibrational levels for these systems are ν' = 12, 22, 31 ± 2, 35 ± 2 and 24 ± 2 of the D 1Π state and ν″ = 0, 5, 8 ± 1, 9 ± 1, and 6 ± 1 of the X1∑ state.

The lowest nine states of NaK have been calculated with large Cl using non-empirical pseudopotentials. A recently developed perturbation treatment of the core—valence polarization and correlation effects is applied. It greatly improves the calculated atomic energies of Na and K; and appears to be very important for energy curves of NaK, leading to an overall good agreement with the experimental results.

NaK, Na and Ca inject SCL election currents into crystals of poly-1,6-di(N-carbazolyl)-2,4-hexadiyne (DCH). An electron mobility (6 ± 2) × 10 3 cm 2 V −1 s − η in chain direction follows. Temperature-dependent injection from Mg yields −3.4 and −5.8 eV for electron affinity and ionization potential of DCH. Absence of injection into PTS is attributed to surface traps.

Potential energy curves of several low lying electronic states of NaK have been determined by the ab initio and pseudopotential methods. The results are in close agreement with published spectroscopic data. In particular, we identify the 3 Π perturbing states suggested from the studies of Loomis and Arvin and of Breford and Engelke.

We report the Gibbs free energy of formation of ThCl4 in (LiK)Cl and we make a comparison with similar data obtained in (NaK)Cl. The thermodynamic data have been obtained from e.m.f. measurements extrapolated down to infinite dilution. The standard potentials of the Th(IV-O) system at 400, 450 and 500°C are respectively equal to 2.52, 2.50 and 2.47 volts vs. Cl 2 2Cl − in the m.f. scale.

Intensity and lifetime measurements on the Ar + laser-induced fluorescence in the D 1 Π-X 1 Σ + system of NaK have been performed to evaluate the variation of the dipole transition moment R with internuclear separation r . It was found that the moment (in debye) can be expressed by the function R ( r ) = −6.0 + 2.3 r in the range 3.6 r

Semiempirical pseudopotentials including core-polarization account quantitatively for core-valence correlation and give accurate results even for relativistic molecules. We discuss the main spectroscopic constants for molecular ions of the type A′A + and AH + (A′, A: Li to Cs) and for the molecules LiH, NaK and LiF.

Microhardness studies were carried out on melt-grown (NaK)Cl crystals. The quenching strains and the difference in the ionic sizes of the cations constituting the mixed system introduced large numbers of defects, viz. dislocations, grain boundaries, etc. The etching experiments and supplementary X-ray studies clearly revealed that the Na + or K + ions are precipitated at the dislocation sites. These phase particles strongly interact with dislocations so as to obstruct the mobility of the latter contributing to the hardening mechanism. Results are compared with solution-grown two-phase mixed NaClKCl pure NaCl and pure KCl crystals.

The d 3 Π 1 ← X 1 Σ + band system of the NaK molecule is investigated by laser excitation spectroscopy in a supersonic nozzle beam. The D 1 Π- d 3 Π perturbation facilitates observation of the nominally spin-forbidden d - X transition. The absolute vibrational assignment for the d 3 Π 1 state is established by measurement of the isotopic shift of bands and the deperturbed molecular constants for this state are obtained. The value of the electronic perturbation parameter describing the spin-orbit D - d interaction is determined from the experiment.

By exciting NaK in a supersonic nozzle beam with the 4765 A argon-ion laser line, we have obtained a set of spectroscopic constants for the X 1 Σ + ground state. In addition, we find evidence for a D 1 Π a a 3 Σ + transition in the region between 6250 and 7100 A. By measuring these bound-continuum fluorescence features, we have determined for the first time spectroscopically the lowest triplet potential curve of an alkali dimer.

The C 1 Σ + -X 1 Σ + transition of NaK following excitation by the Kr + 5309 A laser line is observed. The molecular constants and the potential curve of the C 1 Σ + state are determined. It is shown that the C 1 Σ + state lies above the B 1 Π state. The mechanism responsible for Na and K D-line fluorescence is discussed.