Laser-induced fluorescence spectra

There is little evidence for 1 1 compounds between elements in this group under normal conditions. The diatomic van der Waals molecules, CaMg, SrMg and SrCa, however, have been synthesized by codepositing the atoms from separate sources with argon or krypton into solid matrices at 12 K. These low-T species are identified from their laser-induced fluorescence spectra. The ground-state spectroscopic data for these alkaline-earth dimers form a sensible series between the parent molecules Mg2, Caj and Sr2. ... 

J.M. Andrews and S.H. Lieberman, Neural network approach to qualitative identifications of fuels from laser induced fluorescence spectra. Anal. Chim. Acta, 285 (1994) 237-246. 

Andrews J, Lieberman S. 1994. Neutral-network approach to qualitative identification of fuels and oils from laser-induced fluorescence-spectra. Analytica Chimica Acta 285(l-2) 237-246. 

Figure 1. Dye-laser-induced fluorescence spectra of SRC-1 in an n-heptane matrix at 15 K. In each case, a delay was imposed between the arrival of a laser pulse at the sample and measurement of the actual fluorescence note the difference between the 3-ns and 35-ns spectra at an excitation wavelength of 383.0 nm. Identified compounds BaP, benzo[a]pyrene Pe, perylene. U denotes a compound that cannot be identified because its spectrum is not included in our file of pure-compound...

Figure 10. Laser induced fluorescence spectra of Bal produced by (a) monomeric reaction Ba + CF3I or by (b) dimeric reaction Ba + (CF]I)2. In upper part of figure quantum numbers of vibrational states associated with observed transitions are inrticated.

Very recently Cullin et al. [89b, c] have re-investigated the laser-induced fluorescence spectra produced from phenyl azide and Porter s precursors. Analysis of the rich vibrational-rotational spectra produced in a jet expansion demonstrated that the carrier of the spectrum could not be triplet phenyl nitrene but was more likely cyanocyclopentadienyl radical. 

Fig. 11 Laser-induced fluorescence spectra recorded from Napl-doped PMMA samples (1.2 wt%) after their irradiation with a single pump pulse at 248 nm at laser fluences below a, and above b the corresponding ablation thresholds. For comparison purposes, the spectra have been scaled. The figure also illustrates the approximate deconvolution of the probe spectrum into the emission bands of the suggested species (the Nap2 spectrum is recorded in the photolysis of high-concentration NapI solution, while the NapH/PMMA spectrum is recorded from PMMA doped with 0.08 wt% NapH)...

Fig. 12 Laser-induced fluorescence spectra recorded from Napl-doped PMMA samples (1.2 wt%) after their irradiation with a single pump pulse a at 248 nm and b at 308 nm at laser fluences about 1.5 times the corresponding ablation thresholds...

Fig. 16 Laser-induced fluorescence spectra recorded from NapI/PMMA (0.4 wt%) irradiated with the indicated number of pulses (at 248 nm) at the two indicated fluences...

Figure 17. Laser excitation spectra (up arrows) and dispersed laser-induced fluorescence spectra (down arrows) of the B21.+-X2I.+ transition of SrOH. [Reprinted with permission from ref. 77. Copyright 1993 NRC Research Press.]...

The preparation and low-resolution spectra of a few calcium and strontium alkylamides were reported in 1987 [118]. By replacing NH3 with monoal-kylamines, NH2R [R = —CH3, —C2H5, —CH(CH3)2, and —C(CH3)3] in a Broida oven, the laser-induced fluorescence spectra of the A-X, B-X, and C X transitions (see for example, Fig. 29) were recorded. There was a strong similarity with the spectra of CaNH2 (Fig. 7) although the symmetry is lower than C2l, for the monoalkylamide derivatives. 

Figure 13. Laser-induced fluorescence spectra of the CF3O radical (a) laser excitation spectrum b) dispersed fluorescence spectrum.

Rotational analysis of laser-induced fluorescence spectra. 

To date, the laser-driven sources based on harmonic generation and frequency mixing have been used in a number of experiments to measure radiative lifetimes and to record absorption and laser-induced fluorescence spectra. While some of the anti-Stokes Raman sources have demonstrated high intensity and are being applied to specific problems of impurity detection in plasmas, their general utility in spectroscopy awaits the development of systems with broad tunability. Here, several typical spectroscopic applications of the above VUV and XUV sources are given to illustrate their usefulness. 

The selectively excited molecular levels emit fluorescence spectra that are much simpler than those emitted in gas discharges, where many upper levels are populated. These laser-induced fluorescence spectra are therefore more readily assignable and allow the determination of molecular constants for all levels in lower states into which fluorescence transitions terminate (Sect. 1.8). 

This was demonstrated by Schade [1482], who measured laser-induced fluorescence spectra of diesel oil and gasoline, excited by a nitrogen laser at X = 337.1 nm. Time-resolved spectroscopy exhibits two different lifetimes that are determined by measuring the intensity ratio of the LIF in two different time windows (Fig. 10.25). This time-resolved spectroscopy increases the detection sensitivity for field measurements. Mineral-oil pollutions of 0.5 mg/1 in water or 0.5 mg/kg in polluted soil can be detected [1482]. Using photoacoustic spectroscopy with a dye laser, concentrations down to 10 -10 mol/1 of transuranium elements could be detected in... 

M. Takayanagi, I. Hanazaki, Fluorescence dip and stimulated entission-pumping laser-induced-fluorescence spectra of van der Waals molecules. J. Opt. Soc. Am. B 7, 1878 (1990)... 

Rgure 2 Site-specific, laser-induced fluorescence spectra of pyrene, 4-melhylpyrene (4-MP), B[a]P, and B[fc]F present in a solvent-retained coal liquid (SRC-11) sample measured in a frozen n-octane solution at 15 K. The excitation wavelengths for the PAHs are given. (Reprinted with permission from Yang Y, O Silva AP, Fassel VA, and lies M (1980) Direct determination of poiy-nuclear aromatic hydrocarbons in coai iiquids and shaie oii by laser exited Shpol skii spectrometry, Analytical Chemistry 52 1350-1351 American Chemical Society.)... 

A rotational analysis of the overtone spectrum yielded vibrationally averaged rotational constants of 0.104 0.003 cm and 0.101 0.003 cm for OH-Ar in the Vqh=0 and vqh=2 levels, respectively. The rotational assignments and calculated line positions from the least squares fit are displayed above Fig. 6. The rotational constant for the vibrationless level of the ground state derived from the rotational analysis of the infrared spectrum is in agreement with the value independently obtained by rotational analysis of the features in the laser induced fluorescence spectra about OH A-X 0-0 and 1-0, Bq" = 0.104 0.003 cm". The rotational constant decreases by 0.003 0.003 cm" upon overtone excitation, equivalent to an increase of less than 0.1 A in the OH-Ar bondlength. 

Recently the compact time-resolved (TR) Raman, and fluorescence spectrometers suitable for planetary exploration under NASA s Mars Instrument Development Program have been developed (Sharma et al. 2012). The compact Raman and fluorescence spectrometers consist of custom miniature spectrographs based on volume holographic gratings, and custom miniature intensified CCD cameras. Using a small frequency-doubled Nd YAG pulsed laser (35 mJ/pulse, 20 Hz) and 50 mm camera lens, TR Raman and laser-induced fluorescence spectra of minerals from rare-earths and transition-metal ions in time domain and in the spectral range of 400-800 nm can be measured. 

In 1997, Clouthier et al. presented laser-induced fluorescence spectra of H2C=Si produced by an electric discharge through dilute MeaSi-Ar mixtures . The rotational analysis yielded geometric parameters in good agreement with theoretical predictions (given in brackets) employing TZ(2df,2pd) basis sets and correlation corrections at the CISD level r(C-Si) = 1.706(5) [1.704] A, r(C-H) = 1.099(3) [1.083] A and... 

Fig. 10.51. Laser-induced fluorescence spectra for an experimental tumour (a human colon adenocarcinoma inoculated in rat muscle) and normal surrounding tissue. The rat had been injected with a dose of hematoporphyrin derivative about two days before the investigation. Two excitation wavelengths, 337 and 405 nm, are chosen to illustrate the influence of the wavelength choice [10.185]...

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