Jet-cooled diode laser spectra of CF3Br in the 9.2 microm region and rovibrational analysis of symmetric CF3 stretching mode

Pulsed slit-jet high resolution (up to 0.0009 cm(-1) FWHM) infrared diode laser spectra of CF(3)Br, with natural isotopic abundance, were obtained in the region around 9.2 microm at the rotational temperature of about 50 K. In addition, diode laser spectra at reduced temperature (200 K) were recorded. We present here the rovibrational analysis of the nu(1) fundamental in the range 1075-1090 cm(-1). The fine structure of many P(J) and R(J) clusters has been well resolved for the first time. The assignment of rovibrational transitions has been accomplished up to K = 27, J = 63 for CFBr and K = 33, J = 62 for CFBr. A total of 636 (CFBr) and 880 (CFBr) lines were used in the final fit and a very accurate set of molecular constants, including the quartic centrifugal distortion coefficients for the v(1) = 1 state of both the bromine isotopologues, was obtained. In addition, spectral features belonging to the nu(1) + nu(6)-nu(6) hot band were unambiguously identified and a set of spectroscopic parameters were determined.     

Infrared diode laser spectroscopy of the deltanu=2 band of AlF

A vibrational-rotational spectrum of the deltanu=2 transitions of a high-temperature molecule AlF was observed between 1,490 and 1,586 cm(-1) with a diode laser spectrometer. Measurements were made on the nu=3-1, 4-2, 5-3 and 8-6 bands at a temperature of 900 degrees C. Measured spectral lines were fitted to effective band constants nu(0), B(nu) and D(nu) for each band. Present measurements were made with only one Pb-salt laser diode. Physical significance of the effective band constants is discussed.     

Pressure-induced shift and broadening of acetylene lines in the region 6580-6600 cm-1

Highly accurate measurements of pressure shift and broadening parameters of acetylene absorption lines in the region 6580-6600 cm-1 have been performed by tunable diode laser spectroscopy (TDLS). For these purposes the three channel spectrometer with distributed-feedback diode laser, operated at 1.53 microm was used. The laser is generating pulses of 4-10 ms duration at a repetition frequency of 40 Hz. A temperature-stabilization system, using a thermoelectric cooling unit affords a temperature stability of the order of 10(-4)K in the temperature range from -15 to +50 degrees C. A three channels acquisition system ensured simultaneous real time recording of the sample gas absorption spectrum and of two spectral calibration signals (Fabry-Perot fringes and low-pressure reference lines). We have measured the pressure-induced self-shift and broadening coefficients for six lines of the R-branch in the nu1+nu3 rotation-vibration band of acetylene 12C2H2. The self-shift coefficients have been determined for these lines in the wide pressure region. A non-linear behavior of the pressure dependence of the shift was observed. The temperature exponent n of pressure-induced broadening and shift are reported.     

Mass spectrometry determination of the isotopic composition of uranium hexafluoride

An absolute method for the determination of isotopic composition of substances in multiple collector mass spectrometers was proposed. The detailed analysi of terms used in the method for the determination of the isotopic composition of uranium hexafluoride was given. Parabolic nature of occurring constant measurement error, obtained in theory, was proved by test data for ²³⁵U within a wide range of its concentrations. In order to use the method of measurements in practice, the registration of constant error, through linear discriminatory relations Δc _i (c _i ), preliminary determined using uranium hexafluoride with standard isotopic composition, was proposed. The advantages of the developed method in comparison with the traditional analysis procedures, applied at present, were considered.     

Two-channel opto-acoustic diode laser spectrometer and fine structure of methane absorption spectra in 6070-6180 cm-1 region

We describe the hardware and software of the high-sensitive two-channel opto-acoustic spectrometer with a near infrared diode laser. A semiconductor TEC-100 laser with outer resonator generates a continuous single-frequency radiation in the range of 6040-6300 cm-1 with spectral resolution better that 10 MHz. The newly designed model of photo-acoustic cells in the form of a ring type resonator was used in the spectrometer, and the system allows the measurement of a weak absorption coefficient equal to 1.4x10(-7) cm-1 Hz-1/2 with a laser radiation power of 0.003 W. The methane absorption spectra within a range of 6080-6180 cm-1 were measured with a spectral resolution of 10 MHz and the signal to noise ratio more than 10(3). Six hundred absorption lines were recorded, which is twice as many as in HITRAN-2004. The accurate measurements of the half-width and shift of methane unresolved triplet R3 of 2nu3 band permit us to determine values of the broadening and shift coefficients for CH4-air, CH4-N2, and CH4-SF6 mixtures.     

Infrared spectra of helium clusters seeded with nitrous oxide, 4HeN-N2O, with N=1-80

High resolution infrared spectra of HeN-N2O clusters are studied in the 2200 cm(-1) region of the N2O nu1 fundamental band. The clusters are produced in a pulsed supersonic jet expansion from a cooled nozzle source and probed using a tunable diode laser operating in a rapid-scan mode. Three isotopic forms are used (14N14N16O, 15N14N16O, and 15N15N16O) in order to support the spectral analyses. For clusters up to N approximately 24, the individual spectra are resolved, assigned, and analyzed together with complementary microwave data. Assignments for larger clusters are uncertain due to overlapping transitions, but an approximate analysis is still possible for N approximately 25-80. Compared to helium clusters containing the related CO2 or OCS molecules, the rotational dynamics of HeN-N2O clusters show similarities but also important differences. In particular, HeN-N2O has more irregular behavior in the range of N=6-17, indicating that conventional molecular structure plays a greater role. In general terms, these differences can be attributed to a greater degree of angular anisotropy in the He-N2O intermolecular potential.     

Infrared spectra of the OCS trimer

Infrared spectra of the barrel-shaped trimer (OCS)(3), previously known from its microwave spectrum, are reported for the first time. The observations are carried out in a supersonic slit-jet expansion of a He+OCS gas mixture which is probed with a tunable diode laser. Three rotationally resolved bands associated with the nu(1) fundamental vibration of OCS (2062.20 cm(-1)) are observed, at about 2047, 2053, and 2077 cm(-1). Small perturbations are noted in the 2077 cm(-1) band and may also be present in the 2053 cm(-1) band, which is weak and hence more difficult to analyze precisely. Employing a variety of evidence, we suggest a plausible assignment for the nature of the OCS vibrations in each of the three bands.     

Distribution coefficients for <Superscript>85</Superscript>Sr and <Superscript>137</Superscript>Cs in Japanese agricultural soils and their correlations with soil properties

The performance of several commercially available portable radiation spectrometers containing small NaI(Tl) scintillation detectors has been studied. These devices are used by field inspection personnel to detect and identify illicit radioactive materials. The detection and identification of enriched uranium is an important deterrent to undeclared nuclear proliferation and nuclear terrorism. This study was conducted using a variety of shielded and unshielded uranium sources in a simulated maritime environment. The results indicate adequate identification capability for various uranium enrichments using the manufacturer’s spectral analysis firmware. More sophisticated methods for analyzing the spectra can be applied to these short field measurements to determine the isotopic enrichment.     

Tunable single-photon ionization TOF mass spectrometry using laser-produced plasma as the table-top VUV light source

Here we report on a laser plasma-based tunable VUV photoionization time-of-flight (TOF) mass spectrometer conceived mainly to study complex gaseous mixtures. Ionizing photons at tunable vacuum UV (VUV) wavelengths are generated by a gas-target laser-produced plasma, spectrally dispersed in the range 100–160 nm and efficiently focused onto a sample molecular beam. As a test case, we studied the exhaust gas of a four-stroke moped, a typical example of a complex gaseous mixture. Due to the VUV “soft” ionization, the mass spectra are less congested and more easily interpretable. Substituted benzene derivatives are found to give the most intense signals. Several aliphatic hydrocarbons are also detected. The use of tunable VUV radiation allowed the investigation of the contribution of isomers in the mass spectrum from the onset and shape of the photoionization efficiency spectra. Semiquantitative analysis was performed using known literature data detailing the photoionization cross sections. Our findings suggest that using combined data on the mass/photoionization efficiency spectra may be very helpful for a comprehensive analysis of complex gaseous mixtures.     

Development of a stabilized low temperature infrared absorption cell for use in low temperature and collisional cooling experiments

We have constructed a stabilized low temperature infrared absorption cell cooled by an open cycle refrigerator, which can run with liquid nitrogen from 250 to 80K or with liquid helium from 80K to a few kelvin. Several CO infrared spectra were recorded at low temperature using a tunable diode laser spectrometer. These spectra were analyzed taking into account the detailed effects of collisions on the line profile when the pressure increases. We also recorded spectra at very low pressure to accurately model the diode laser emission. Spectra of the R(2) line in the fundamental band of 13CO cooled by collisions with helium buffer gas at 10.5K and at pressures near 1 Torr have been recorded. The He-pressure broadening parameter (gamma(0) = 0.3 cm(-1) atm(-1)) has been derived from the simultaneous analysis of four spectra at different pressures.     

Analysis of solid uranium samples using a small mass spectrometer

A mass spectrometer for isotopic analysis of solid uranium samples has been constructed and evaluated. This system employs the fluorinating agent chlorine trifluoride (ClF₃) to convert solid uranium samples into their volatile uranium hexafluorides (UF₆). The majority of unwanted gaseous byproducts and remaining ClF₃ are removed from the sample vessel by condensing the UF₆ and then pumping away the unwanted gases. The UF₆ gas is then introduced into a quadrupole mass spectrometer and ionized by electron impact ionization. The doubly charged bare metal uranium ion (U²⁺) is used to determine the U²³⁵/U²³⁸ isotopic ratio. Precision and accuracy for several isotopic standards were found to be better than 12%, without further calibration of the system. The analysis can be completed in 25 min from sample loading, to UF₆ reaction, to mass spectral analysis. The method is amenable to uranium solid matrices, and other actinides.     

Laser excited atomic fluorescence spectrometry — a review

This review focuses on the development of new instruments, and new applications of laser excited atomic fluorescence spectrometry, LEAFS, in recent years since the last published reviews. Such developments include solid-state tunable lasers, deep UV tunable lasers, the use of charge coupled detectors (CCDs), and the applications of LEAFS for trace metal determination in various samples. The advent of diode lasers with their now somewhat improved range of wavelengths and power output, provides opportunities for research and applications in LEAFS. The further development of the coupling of second and third harmonic crystals to pulsed diode lasers shows promise for compact and robust instrumentation. There have been no recent instrumental developments that might provide more isotopic selectivity beyond the elements like uranium where the spectral isotope splitting is greater than most elements, but laser diodes could provide this due to their potential to provide an output with very narrow spectral bandwidth. The advent of optical parametric oscillator-based lasers has enabled LEAFS to be much more practical then in the past when dye lasers were used. This should be the harbinger of more applications of LEAFS to complex real sample analyses that can not be done by other techniques for reasons of sensitivity or selectivity. Array detectors provide an additional degree of freedom by provision of more spectral information more rapidly, which should aid the study of complex samples that might produce complex background problems. The recent literature indicates that the sensitivity, selectivity and ease of method development of LEAFS is well-established, and that there are no substantial analytical disadvantages to the technique beyond the instrumental limitations associated with the single element at a time mode of operation and the complexity of the laser systems. Laser technology continues to develop rapidly, which heralds a bright future for LEAFS.     

Characterization of uranium particles produced by hydrolysis of UF6 using SEM and SIMS.

Environmental sampling (ES) is a powerful technique used by safeguards inspectors of the International Atomic Energy Agency and the European Safeguards Office for the detection of undeclared nuclear activities. Since its implementation in the 1990s, ES has proven to be very sensitive and effective. Considering the consequences, the measurements should be carried out under a quality management programme. At the Institute for Reference Materials and Measurements, a new production method is under development for the preparation of reference uranium particles from well-certified UF6, allowing uranium particles with certified isotopic abundances to be prepared that are representative of those found in uranium enrichment facilities. Using an aerosol deposition chamber designed and built for the purpose, particles are formed by the hydrolysis of UF6 and their morphology and (isotopic) composition measured using SEM-EDX and SIMS. The SEM measurements show that by varying the relative humidity of the air in the reaction chamber, the morphology of the particles can be changed. By making a distribution map of the chemical composition of the particles, the relationship between fluorine and uranium as main constituents of the particle could be established. The presence of fluorine is a valuable indicator for the occurrence of nondeclared enrichment activities.     

Diode laser spectroscopy of the ν8 band of the SF5Cl molecule

Diode laser spectra of SF(5)Cl have been recorded in the nu(8) band region at a temperature of ca. 240 K, a pressure of 0.25 mbar and an instrumental bandwidth of ca. 0.001 cm(-1). Four regions have been studied: a first one in the P-branch (906.849-907.687 cm(-1)), a second one in the Q-branch (910.407-910.944 cm(-1)), and two other ones in the R-branch (913.957-914.556 and 917.853-918.705 cm(-1) ). The whole nu(1)/nu(8) dyad of SF(5)35Cl has been previously recorded in the group of Professor H. Burger in Wuppertal, thanks to a Fourier transform infrared spectrometer. These data have thus been combined with our diode laser ones in the aim of refining the analysis. We used an effective Hamiltonian developed up to the fourth order and a set of programs called C(4nu)TDS. One thousand three hundred and forty-six transitions for nu(1), 495 (FTIR: 351; diode laser: 144) transitions for nu(8), and 406 ground state combination differences have been assigned and fitted. A global fit has been obtained with a rms of 0.00081 cm(-1) for the nu(1) band, 0.0012 cm(-1) for the FTIR data of the nu(8) band, 0.00055 cm(-1) for the diode laser data of this same band, and 0.00064 cm(-1) for the ground state. It appears that more data (for instance, using a supersonic jet) are still necessary to obtain a completely satisfactory analysis of the nu(8) region.     

Concentration measurements of ozone in the 1200-300ppbv range: an intercomparison between the BNM ultraviolet standard and infrared methods

Simultaneous ultraviolet (UV) and infrared (IR) measurements of ozone concentration in air in the 1200-300 ppbv range have been performed using the ultraviolet absorption in the Hartley band at 0.2537 microm and the infrared absorption of a doublet at 9.507 microm in the nu(3) vibration-rotation band. Infrared concentration measurements were achieved using the tunable diode laser spectrometer of LPMA in Paris with interferometric control of the emitted wavelength while the UV concentration measurements were performed with the 49PS Megatec ozone generator of the Bureau National de Metrologie (BNM). The simultaneous recording of spectra of a reference cell filled with pure distilled ozone and of a low concentration mixture inside a long absorbing path Herriott cell allows to carry out infrared concentration measurements with an accuracy of the same order as the ultraviolet ones and provides the instrumental parameters of the spectrometer corresponding to each concentration measurement, which reduces systematic errors. Within the respective absolute uncertainties proper to the two techniques, no systematic discrepancy was evidenced between the IR and the UV measurements. The ozone ultraviolet absorption coefficient value determined by Hearn (308.3 +/- 4 cm(-1)atm(-1)) and used by the BNM and the National Institute of Standards and Technology (NIST) is confirmed by the present work.     

Infrared laser spectrometer with balanced absorption for measurement of isotopic ratios of carbon gases

Measurement of the isotopic compositions of carbon dioxide and methane is a powerful tool for quantifying their atmospheric sources and sinks, which is especially important considering the dramatic increase in these greenhouse gases during the industrial era. Laser absorption spectroscopy is a technique which has demonstrated the high sensitivity needed for isotopic measurement. A significant problem in the spectroscopic measurement of isotopic abundances is the large difference in concentrations of the major and minor isotopic constituents. The measurement of two isotopic species using lines of similar strength but very unequal concentrations leads to low precision, with either the minor constituent having too small an absorption depth, or the major constituent having too great an absorption depth. If lines with unequal strength are chosen to compensate for the absorption depth imbalance, then precision tends to suffer due to the greater temperature sensitivity of the weaker line strength. We describe the development of a compact instrument for isotopic analysis CO2 and CH4 using tunable infrared laser absorption spectroscopy which combines novel optical design and signal processing methods to address this problem. The design compensates for the large difference in concentration between major and minor isotopes by measuring them with pathlengths which differ by a factor of 72 within the same multipass cell. We have demonstrated the basic optical design and signal processing by determining delta13C (CO2) isotopic ratios with precision as small as 0.2/1000 using a lead salt diode laser based spectroscopic instrument.     

FTIR identification of the nu4(sigmau) and nu6(piu) modes of linear GeC3Ge trapped in solid Ar

GeC 3Ge was previously (1) produced by the dual laser ablation of germanium and carbon rods, and the nu 3(sigma u) carbon-carbon stretching fundamental was assigned at 1920.7 cm (-1). This paper presents results from new experiments that have enhanced the production of the molecule via laser ablation of a single sintered germanium-carbon rod, thus enabling the identification of two additional infrared active vibrational fundamentals. Ge participates strongly in one of these, the nu 4(sigma u) mode, and the corresponding Ge isotopic shifts reported here are the first for a germanium-carbon species. GeC 3Ge was produced by trapping the products from the laser evaporation of the Ge-C rod, in solid Ar at approximately 10 K, and recording the FTIR (Fourier transform infrared) spectra. Comparison of (70,72,73,74,76)Ge and (13)C isotopic shift measurements with the predictions of density functional theory calculations (DFT) at the B3LYP/cc-pVDZ level confirms the identification of the nu 4(sigma u) stretching fundamental at 735.3 cm (-1) and the nu 6(pi u) bending fundamental at 580.1 cm (-1) for linear GeC 3Ge.     

Boron isotopic measurements from spectrally filtered non-gated molecular spectra induced by laser ablation

Spectral analysis of molecular emissions from laser-produced plasmas can augment laser-induced breakdown spectroscopy measurements, in which only atomic spectra are typically considered. Molecular isotopic shifts can be significantly greater than the respective atomic isotope shifts, enabling isotopic measurements with lower spectral resolution and in atmospheric pressure conditions. Successful isotopic measurements using molecular spectra have been made in the past by gating off the atomic emissions, or by the use of a femtosecond laser in conjunction with a non-gated detector. We report that it is possible to make accurate isotopic measurements by use of molecular emissions from non-gated spectral data even when nanosecond lasers are used. We demonstrate this capability by measuring the isotopic composition of boron-containing samples using 10-ns, 1064-nm pulses from an Nd:YAG laser and a non-gated detector. We investigate how the accuracy and precision of the multivariate calibration model used in the isotopic reconstruction is influenced by the spectral data analysis. The effect of the selection of the spectral region of interest for analysis and the optimization of a numerical spectral filter is studied. It is shown that the accuracy of isotopic reconstruction can be greatly improved by spectral filtering, and that it is relatively insensitive to laser pulse duration.     

UF6 plasma chemistry reconstitution experiments using high-temperature fluorine

Prior results indicate techniques have been developed for fluid mechanical confinement of high-temperature uranium hexafluoride (UF₆) plasma for long test times while simultaneously minimizing uranium compound deposition on the walls. Follow-on investigations were conducted to demonstrate a UF₆/argon injection, separation, and reconstitution system for use with rf-heated uranium plasma confinement experiments applicable to UF₆ plasma core reactors. A static fluorine batch-type regeneration test reactor and a flowing preheated fluorine/UF₆ regeneration system were developed for converting all the nonvolatile uranium compound exhaust products back to pure UF₆ using a single reactant. Pure fluorine preheat temperatures up to 1000 K resulted in on-line regeneration efficiencies up to about 90%; static batch-type experiments resulted in 100% regeneration efficiencies but required significantly longer residence times. A custom-built, ruggedized time-of-flight (T.O.F.) mass spectrometer, sampling, and data acquisition system permitted on-line quantitative measurements of the UF₆ concentrations down to 30 ppm at various sections of the exhaust system; this system proved operational after long-time exposure to corrosive UF₆ and other uranium halides.     

Inelastic processes induced by collisions in rotational levels of OCS perturbed by OCS,HE and AR

We present results of infrared linewidth measurements at room temperature for OCS diluted in Ar and He using a tunable diode laser in the 4.7 μm spectral region. Information on the intermolecular potential is obtained and compared with results of semiclassical calculations by Liu and Marcus and IOS calculations of S. Green.