Glenn A. McRae

The high-resolution infrared spectrum of iodine monochloride

Abstract The high-resolution infrared spectrum of iodine monochloride has been observed in absorption by Fourier transform spectroscopy. About 750 rovibrational transitions for the two isotopomers I 35 Cl and I 37 Cl have been assigned. The new infrared data were combined with millimeter-wave transition frequencies from the literature to yield precise Dunham coefficients, Y ij , for the X 1 Σ + electronic ground state of ICl. In addition, mass-reduced Dunyam constants, U ij , have been derived.

Decomposition of highly vibrationally excited CDCl3

Decomposition of highly vibrationally excited CDCl3 was studied in the time domain by measuring laser‐induced fluorescence from one of the decomposition products CCl2 or by observing luminescence from CCl2 radical fragments produced in the A(1B1) state following IR excitation. It is shown that highly vibrationally excited CDCl3 can be made via two different routes: i/mple optical absorption of an incident 13CO2 laser pulse or through collision‐moderated energy pooling coupled with photon absorption. Higher fluence measurements are consistent with the former and support previous claims that the infrared multiphoton decomposition probability for CDCl3 is pressure independent. At a lower fluence the vibrational up‐pumping mechanism apparently relies heavily upon collisions, which supports other claims that the decomposition probability is pressure dependent. The results of the present work reconcile these previous disparate claims. Furthermore, there is an indication that the vibrational energy transferred ...

Determination of hydrogen and deuterium in Zr-2.5Nb by laser ablation

Abstract Laser ablation is investigated as a microsampling technique for determining the content and spatial distribution of hydrogen and deuterium in zirconium alloys. Zr-2.5wt%Nb (Zr-2.5Nb) material is ablated under vacuum with the 1.06 μm output of a Nd:YAG laser. Elemental H and D in the ablation plume are detected in a time-of-flight mass spectrometer (TOF-MS) following photo-ionization via the 1s–2s two-photon resonance near 243 nm. The laser/surface interaction is shown to be characterized accurately by a simple thermal model and the subsequent ablation is consistent with volume evaporation from the melted alloy. Elemental compositions in the ablation plume are found to represent those in the alloy. The analytical capabilities of laser ablation sampling are studied and discussed using various Zr-2.5Nb samples with known deuterium concentration gradients and bulk deuterium content.

Determination of the 1s–2s two-photon excitation cross-section in atomic hydrogen

Abstract Hydrogen atoms are ablated from zirconium alloys into the gas phase by a pulsed Nd:YAG laser and photo-ionized with three photons at 243 nm via the two-photon 1s 2 S 1/2 –2s 2 S 1/2 resonant transition. A determination of the effective 1s–2s two-photon excitation cross-section is necessary to quantify the hydrogen atom density in the ablation plume. A measurement of the ion signal vs. photo-ionization beam energy is fitted to an expression derived from the rate equations. The temporal and spatial properties of the photo-ionization laser beam, transit of the H atoms through the beam, and detector geometry are taken into account. The effective two-photon cross-section for this experimental configuration, derived with the rate equation formalism, is 3.3±0.8×10 −28 cm 4 W −1 . This compares well with the ab initio prediction of 5±1×10 −28 cm 4 W −1 under these experimental conditions.

Laser ablation with resonance ionization for determination of hydrogen in zirconium

Corrosion and hydrogen ingress in zirconium alloys can lead to hydride blister formation at localized areas and possible delayed hydride cracking. Laser ablation is being investigated in our laboratory as a method to determine the content with the 1.06 μm or 355 nm output of a Nd:YAG laser. The elemental H and D in the ablation plume are detected in a time‐of‐flight mass spectrometer following photo‐ionization via the two‐photon resonance near 243 nm. The ablation is accurately described by a simple laser‐heating model for fluences below 3 J/cm2 at beam center. Ablation rates were found to range from a few to hundreds of A per shot, varying exponentially with fluence. Laser ablation depth profiling in thin oxide films has yielded qualitative information about the H distribution. Various surface techniques such as Nuclear Reaction Analysis (NRA) and laser profilometry are used to support these conclusions.

Profiling of Hydrogen in Zirconium Surfaces by Laser Ablation with Resonance Ionization

Elemental distributions in the bulk and metal oxide surface layers of zirconium alloys play key roles in the fracture toughness of the alloys. In particular, localized hydrogen build-up leads to hydride formation and delayed hydride cracking. Parts per million levels of H in Zr have been detected using the 1.06 μm or 355 nm output of a Nd:YAG laser for ablation followed by 2+1 resonance ionization detection of H and D. Analysis of the ablation plume has shown that it consists predominately of atomic species in thermal equilibrium between 2000 and 3600°C. Ablation of thin foils has shown that the ablation rate is on the order of mono-layers per shot and increases exponentially with increasing fluence. Laser ablation depth profiling results of H distributions in an anodically grown oxide film compare qualitatively with nuclear-reaction-analysis profiling of the same sample.