Ar H2O Research Articles

Kinetic study of high-pressure Ar–H2O mixtures excited by relativistic electrons

Dissociation of the H2O molecule by collisions with metastable argon (3P2) was shown a few years ago to lead to the excitation of the first vibrational levels of A 2Σ+ excited state of OH. The present work consists of a detailed kinetic study of an e-beam excited Ar–H2O mixture to evaluate the potential interest of that reaction scheme for laser applications. In this study, we have mainly shown that OH* (A 2Σ+) is populated by an Ar++H2O pathway too and we give an estimate for the OH* (A 2Σ+) and OH (X 2Π) formation branching ratios. We have also estimated that Ar*2+H2O is a minor OH* pathway. These results and measurements of main reaction rates permitted us to give a kinetic model where the predicted time dependence of population are in good agreement with the experimental result. The feasibility of a radical laser based on the collisional dissociation scheme of molecules is discussed.

Structuring of bubble overlays by reactive sputter etching in an Ar–H2O atmosphere

The structuring of magnetic bubble propagation overlay patterns by sputter etching, using photoresist as a mask, becomes imperfect for high definition structures. In the past, reactive sputter etching in an O2 containing atmosphere has been introduced as an alternative, the mask material being a metal such as V, Ti, or Cu. The present paper describes how the etch rate ratio between NiFe and Ti can be considerably increased to at least 10 by replacing oxygen with water vapor. The masking Ti layer can than be extremely thin, which has a beneficial effect on the patterning accuracy.

Fluorescence and dissociative energy transfer in high pressure Ar–HCN mixtures excited by relativistic electrons

Studies of the radiation from Ar–HCN and Ar–H2O mixtures, excited by relativistic electrons from a Febetron 706 electron gun, are presented. The energy deposited by the electrons channels rapidly into the Ar* and Ar2* states; then by dissociative collisions with HCN it is transferred partly into the CN(B) state and partly into a reservoir state [most probably the CN(A) state] with near unit efficiency. Fluorescence emission from the electronic states A (2Πi) and B (2Σ+) of the CN radical, as well as the emission from the Ar2* excimer state, were measured for an Ar pressure range of 750–9000 torr [15–180 psi (absolute)], and an HCN pressure range of 0.2–13 torr. The quenching rates of Ar* metastable and the Ar2* excimer states, by collision with HCN molecules, were measured to be 6×10−10 and 1×10−9 cm3 sec−1, respectively. Our results suggest that population inversion can be achieved by collisional dissociation of simple molecules with excited rare gas atoms and excimers. Indeed the peak CN(B) population density was found to be 1.5×1015 cm−3, which corresponds to an optical gain for the B–X transition of 0.4 cm−1 if the ground state is empty. A computer kinetic model is presented that explains the time dependence and intensity of the CN(B) emission. In Ar–H2O mixtures the reaction rate for quenching of Ar2* excimer by H2O molecules is extremely high; however, the yield into the OH(A 2Σ+) is only 3%.

A potential hydroxyl ultraviolet laser

A strong emission band extending from 3060 to 3120 Å was observed following proton beam excitation of an Ar-H 2O mixture. This emission band was assigned to the transition of OH( A 2 Σ +) υ=0 → OH( X 2 Π) υ=0 . At high argon partial pressure (> 200 torr), the precursor of this emission band is believed to be the argon excimer Ar ★ 2(1 u). The fluorescence efficiency of Ar-H 2O is estimated to be a factor of 4 times that of Ar-N 2. Development of a highly efficient, tunable uv laser by e-beam pumping is promising.

Laser scattering measurements of droplet growth in binary mixtures. II. H2O and argon H2O and helium

Water droplet growth rates in a Wilson cloud chamber were measured in Ar–H2O and He–H2O media. These rates were determined in the size range 0.45–10.0 μm by detection of oscillations in the intensity of polarized light from a He–Ne laser source scattered at 30° by the droplet population. Pressure and initial temperature were measured in the chamber for use in the computation of three droplet growth theories for comparison to experiment. Experiments were conducted in supersaturations ranging from 1.04 to 3.45.

Absolute intensity measurements for the 2·7 μ band of water vapor in a shock tube

The apparent spectral absorption coefficients of the H 2O infrared bands in the vicinity of 2·7 μ were measured in a shock tube behind reflected shock waves in an Ar-H 2O mixture. By interrupting an infrared beam at a 60 kc rate and projecting this beam across the shock tube to a monochromator, it was possible to measure simultaneously both emission and absorption of H 2O at 1000°K. The spectral absorption coefficients obtained from emission measurements averaged 9·8 per cent higher than absorption coefficients obtained from absorption measurements, probably due to experimental errors (smaller than usually encountered in shock tube measurements). At 1933°K experimental difficulties precluded simultaneous measurement of infrared emission and absorption, so measurements were restricted to emission. The apparent absorption coefficients were integrated to give the integrated absorption coefficients for the collection of bands near 2·7 μ. Integrated absorption coefficients were 49·8 cm -2 atm -1, 54·7 cm -2 atm -1, and 31·6 cm -2 atm -1 for absorption at 1000°K, emission at 1000°K, and emission at 1933°K, respectively. The two values at 1000°K were in good agreement with those of Goldstein, who made no measurements above this temperature.