Fourier transform IR measurements of Langmuir–Blodgett monolayers have been made with both grazing incidence reflection and transmission techniques. The reflection arrangement at incident angles from 85° to 88° has the electric field component perpendicular to the substrate surface while the standard transmission arrangement has the electric field component in the plane of the film. These techniques were used to explore the anisotropic arrangement of cadmium arachidate molecules perpendicular and parallel to the monolayer plane. The implication of these results for characterizing the orientational anisotropy of chemical groups in thin polymer films is also discussed. In addition, the question of uniaxial and biaxial orientation in the monolayer plane was addressed because of the importance of intermolecular packing on both the extent and rate of polymerization in unsaturated fatty acid monolayer components which form synthetic membranes.

It is reported that thin films of polyimide are efficiently etched in air at pulsed excimer laser wavelengths of 248, 308, and 351 nm. Etch rate versus incident fluence data are found to obey a Beer–Lambert etching relation. Sharp laser fluence thresholds for significant etching are found to correlate with the wavelength-dependent absorption coefficient. The absorbed energy density required to initiate significant etching is found, within experimental error, to be independent of the wavelengths examined. It is felt that this information demonstrates the predominantly thermal nature of the laser etching mechanism. Additionally, infrared spectroscopy and coupled gas chromatography/mass spectroscopy were used to identify several gases evolved during pulsed laser etching of polyimide in both air and vacuum.

Iodine, bromine, and chlorine have been determined by means of neutron activation analysis in a series of aerosols and rain‐water samples collected in Hawaii. Five‐milliliter samples of rain water are used in the analytical procedure, and no chemical treatment is required before pile irradiation. Freedom from errors due to contamination and species‐specific chemical steps is thus assured. The ratio I/Cl in the aerosols and rain water is more than 100 times greater than published values for sea water, but the ratio Br/Cl is the same as that for sea water within a factor of 2. The seven samples of rain water, collected in October and November 1961, and the eight samples of aerosols, collected from a light aircraft in May 1962, show (1) that I/Cl is greater in rain by a factor of 3, (2) that Br/Cl is greater in rain by a factor of 2, and (3) that I/Br is greater in rain by a factor of 1.5.

The nature of uv ablation of organic polymers is discussed in terms of a pseudo-zeroth-order rate law of the form dx/dt = k0e−(Eact/kT), where Eact is assumed to be the strength of the weakest bonds in the polymer and T is the local temperature increase from the incident laser pulse. Equations derived from previous models that assumed nonthermal photodecomposition were duplicated from this photothermal model. Even for the simple case of single-photon absorption, nonideal behavior is affected by radiationless decay, pulse length, and thermal diffusion. These effects were probed. Results indicated that thermal diffusion may have a significant effect on the threshold fluence and to some degree on the shape of the etch depth versus fluence curve. Absorption dynamics (saturation and radiationless decay) appear to be the dominant factor in determining the functional dependence of etch depth on fluence. As a result of competition between absorption saturation and radiationless decay, the penetration depth is intensity dependent. High fluence as well as short temporal pulses (subnanosecond) penetrate more deeply into the polymer than predicted by simple Beer’s law absorption. The apparent existence of an optimum pulse length, for a given absorbing system, is another result of the absorption dynamics.

The effect of pulse repetition rate on polymer ablation was studied experimentally and theoretically for polyimide and 8230 photoresist, a polymethylmethacrylate (PMMA)-based polymer. Both the experimental data and the theoretical model showed a distinct tendency for increased repetition rate to decrease the ablation threshold, without substantially altering the absorption coefficient. This was attributed to heating of the sample sequentially by the laser pulses and the magnitude of the effect is proportional to the square of the absorption coefficient. Polyimide, with an absorption coefficient of , is expected to exhibit the repetition rate effect in the range of tens to hundreds of kilohertz; hence the effect has not heretofore been observed. The PMMA-based photoresist, on the other hand, exhibits the effect at a much lower repetition rate, owing to the smaller effective absorption coefficient.