Glenn A. Laguna

Real-time detection of methyl radicals by diode laser absorption at 608 cm−1☆

Abstract A time-resolved technique has been developed for the detection of CH3 radicals in the gas phase by diode laser absorption at 608 cm−1 on a rotation-vibration transition of the v2 mode of CH3. The usefulness of the technique as a probe of the reaction kinetics is demonstrated by the measurement of the recombination rate of CH3 radicals and the third-body reaction rate of CH3 with O2 at room temperature.

Infrared spectrum and potential constants of silicon tetrafluoride

Doppler‐limited tunable diode laser spectra of ν4 of 28SiF4 have been analyzed and the spectroscopic constants determined. In contrast to most earlier low‐resolution studies, the Coriolis constant ζ4, when combined with ζ3 as obtained from previous laser spectroscopy, yields a zeta sum that is within 5% of the expected harmonic value of 1/2. The band origins of 12 overtones and combinations have been obtained from Fourier‐transform spectra (0.04 cm−1 resolution), resulting in estimates of the anharmonicity constants and harmonic frequencies. From the Coriolis constants and the isotope shifts in ν3 we have redetermined the general quadratic force field of SiF4.

Direct absorption measurement of the spin—orbit splitting of the ground state in atomic fluorine

Abstract We have measured the three hyperfine components of the spin—orbit split (2P 3 2 → 2P 1 2 ) ground state in atomic fluorine by diode laser absorption spectroscopy. The measurement improves the accuracy of the two lines previously reported (404.175 and 403.969 cm−1), with the third line at 404.210 cm−1. This confirms the spacing of the hyperfine components measured by EPR, and establishes diode laser absorption as a viable technique for determining F-atom concentrations.

The 3v3 overtone band in UF6

Abstract We report the observation of the spectrum of the 3 v 3 Q branch in UF 6 at both low (1.4 cm −1 ) and high (0.004 cm −1 > resolution. The most prominent feature of the spectrum is the five-sub-bandheads between 1875.4 and 1875.6 cm −1 . The transition strength for 3 v 3 is Γ 0,3 = 3.8 × 10 −2 km mole −1 .

Reactions of uranium hexafluoride photolysis products

This paper confirms that the ultraviolet photolysis reactions of UF6 in the B band spectral region is simple bond cleavage to UF5 and F. The photolysis products may either recombine to UF6 or the UF5 may dimerize, and ultimately polymerize, to solid UF5 particles. We use four methods to set an upper limit for the rate constant for recombination of kr<2.0×10−12cm3 molecule−1 s−1. We measure the rate constant for UF5 dimerization to be kd=(1.0±0.2)×10−11 cm3 molecule−1 s−1. The principal method employed in these studies is the use of diode lasers to monitor, in real time, the changes in density of the species UF6 and UF5 after laser photolysis of the UF6 gas sample.

Source noise reduction in diode laser spectroscopy using the Faraday effect

Polarization rotation via the Faraday effect was demonstrated for the first time as a technique for reduction of source noise in tunable diode laser spectroscopy. The technique was fully characterized by experiments and computer modeling. A comparison to other noise reduction techniques reveals that polarization rotation is potentially the most sensitive.

The absorption spectrum of laser-produced UF5 molecules in the 350–700 nm region

Abstract UF 5 molecules are generated from the laser photolysis of UF 6 samples in an absorption cell and the low-resolution absorption features in the 350–700 nm region of the UF 6 photodissociation products have been characterized.

Reactions of methyl and ethyl radicals with uranium hexafluoride

We have measured the rates of reaction of both methyl and ethyl radicals with uranium hexafluoride (UF6) in the gas phase. The method we used was to photolyze samples of UF6 in the presence of either methane or ethane. The radicals produced by reaction of fluorine atoms with these species then react with either themselves or with UF6. We inferred the rate constants from ratios of the reaction products and the published rate constants for radical recombination. The diagnostic technique was gas chromatography. The resulting rate constants for reaction with UF6 were (1.6±0.8)×10−14 cm3 molecule−1 s−1 for methyl radicals and (4±2)×10−11 cm3 molecule−1 s−1 for ethyl radicals.

The homogeneous rate constant for the recombination of fluorine atoms with F2 as the third body

Abstract The rate constant for the homogeneous recombination of F-atoms with F2 as the third body was found to be (3.6 ± 1.4) × 1014 cm6/mol2s at 300 to 320 K. The corresponding rate constants with He and Ar as third bodies were also measured.

Absorption sensitivity enhancement in methyl fluoride at 1200cm −1 using Stark polarization rotation

Polarization rotation using a modulated electric field is demonstrated in methyl fluoride vapor as a technique to reduce source noise in diode-laser absorption spectroscopy. A comparison of this technique with amplitude modulation and Stark modulation is presented, showing that this technique decreases the effect of source noise and thus provides improved sensitivity. A discussion is presented of the magnitude of the polarization rotation for different J, K rotational transitions that occur in a symmetric top. The effect of the crossing angle of the polarization analyzer on the polarization rotation signal and the source-noise reduction is studied in order to obtain the operating conditions for maximum signal-to-noise ratio.