H. M. Adams

The multiphoton absorption and decomposition of fluoroform‐d: Laser isotope separation of deuterium

Multiphoton absorption (MPA) studies of fluoroform‐d, a molecule of interest for potential laser based hydrogen isotope separation processes, are reported for CDF3 pressures 0.2–1.3 kPa, and for a variety of 10 μm CO2 laser lines with pulse widths of 2 or 6 ns and fluences within the range 10−3–70 J/cm2. Unlike SF6, no red shift of the MPA spectrum relative to the small signal spectrum was observed at high fluence. Selective multiphoton decomposition (MPD) experiments using the 10R(26) line, 6 ns pulse to excite the CDF3 component in natural‐abundance CHF3 (∼ 150 ppm D/H) at a pressure of 13.3 kPa resulted in the recovery of water enriched up to 30% in deuterium—a measured isotope enrichment of ⩾2000 fold. This demonstrates that a product, highly enriched in deuterium, can be recovered from the selective MPD of fluoroform.

Short-pulse CO(2) laser for photochemical studies.

A line-tunable CO(2) laser system is described producing repeatable pulses with selectable widths from 2 to 60 nsec. High energy contrast ratio (minimum of 10) is achieved in both the P and R branches of the 9- and 10-microm bands making this system a valuable source for photochemical studies.

CO2 laser‐induced multiphoton absorption of fluoroform‐d: The effects of collisionsa)

Studies of the multiphoton absorption of the 10 μm R(26) CO2 laser line by fluoroform‐d have been extended to laser pulse widths (Δτ) of 60 ns over the range of pressures P=0.33 to 2.00 kPa. Comparison with earlier studies with Δτ=2 and 6 ns shows that for all fluences Φ the cross section σ=σ(Φ, PΔτ), which means that σ scales with the number of collisions during the pulse. Log–log plots of σ(Φ) vs Φ (P, Δτ fixed) show a bend at a fluence Φc. For Φ<Φc collisions appear mainly to induce rotational relaxation to fill the hole ‘‘burned’’ by the laser in the ground state rotational distribution. For Φ≳Φc the role of collisions is more complex and likely involves intramolecular relaxation processes.

Intensity dependence of CO2-laser-induced multiphoton absorption and decomposition of monomethylamine

Abstract The infrared multiphoton absorption (MPA) and decomposition (MPD) of monomethylamine have been studied using temporally smooth CO 2 -laser pulses of 6,9 and 40 ns fwhm. Both MPA and MPD depend on gas pressure (0.267–1.33 kPa) at each pulse width; but results for different pulse widths did not simply scale with collision number. At each pressure, MPA and MPD depend on laser-pulse intensity as well as fluence confirming the suggestion of previous workers.

Microcomputer photoacoustic data-acquisition system for multiphoton absorption

A simple and inexpensive microcomputer data‐acquisition system is described for the investigation of the absorption of infrared photons using a photoacoustic detector. The system produces a graphic display of the results during an experiment and permits the operator to correct procedural errors.

Surface profiling of lithium with a laser-desorption mass-spectrometer microprobe

A laser-desorption mass-spectrometer microprobe has been developed to profile Li distributions on the crevice surfaces of Cr-plated rolled-joint hubs. A single laser pulse is used to desorb and ionize the surface species followed by detection of Li(+) in a time-of-flight mass spectrometer. Images of the surface Li distribution are obtained with a resolution of <10 microm. These images are directly compared with Li images from the more conventional secondary ion mass spectrometry technique and evaluated with respect to surface topographical features measured by secondary electron microscopy and atomic force microscopy. The laser-desorption images are shown to provide the same qualitative information as that available from secondary ion mass spectrometry.