Addition Of Helium Research Articles

Effects of CO2, He, and N2 on the Lifetimes of the 00°1 and 10°0 CO2 Laser Levels and on Pulsed Gain at 10.6 μ

Relaxation times of the 00°1 and 10°0 CO2 vibrational levels and the afterglow gain at 10.6 μ were studied by a pulsed-gain technique, for pure CO2, CO2:He, and CO2:N2 gas mixtures in 22-mm- and 34-mm-bore nonflowing laser amplifiers. Measurements of the exponential rise, τr, and decay, γd, times of the afterglow gain pulse were made using a cw 10.6-μ CO2 laser as the amplifier input radiation source. Evidence is presented to support the interpretation of τr and τd as measures of the effective lifetimes of the 10°0 and 00°1 CO2 laser levels, respectively. For the case of a pure CO2 gas in the pressure range from 1 to 8 Torr, the measured τr and τd values vary from 50 to 250 μsec and 0.3 to 2.5 msec, respectively. Both 1/τ00°1 and 1/τ10°0 increase almost linearly with increasing CO2 pressure for P>4 Torr. Collision cross sections for volume quenching in pure CO2 are computed to be σ00°1=2.86×10−19 cm2 and σ10°0=1.62×10−18 cm2, assuming Tgas=300°K. Addition of helium to CO2 causes essentially no change in τ00°1 but results in a substantial decrease in τ10°0. The measured collision cross section for quenching of the 10°0 level population by He is (σ10°0)He=1.04×10−18 cm2, about two-thirds of that obtained for CO2−CO2 collisions. Nitrogen, on the other hand, causes an increase in both τ00°1 and τ10°0 by much as a factor of two at P>5 Torr. The peak values of amplifier gain in the afterglow, Gp, in general, are higher and depend more critically on tube bore than those obtained for cw discharges. The relative values of optimum Gp for CO2, CO2:He, and CO2:N2 are consistent with those obtained from cw gain measurements.

A spectroscopic study of low density cesium and cesium-helium discharges

Excitation temperatures and Saha temperatures are determined for an r.f. excited cesium discharge in the electron density range from 2·5x10 9−3 x 10 11/cm 3. The consequence of self-absorption of both resonance and nonresonance states in measuring temperatures is discussed. It is shown that cesium ion excitation is inversely related to ion density and that this excitation cannot be described by a “ temperature”. Addition of helium over the pressure range 0·1–10 torr has no effect on ionization or cesium excitation other than to allow observation of Cs spectra at a lower pressure than is possible in pure cesium. A discussion of the utility of these observations in describing the non-equilibrium state of the discharge is included.

Helium as a ground-water tracer

Laboratory and field experiments were conducted with helium as a ground-water tracer. Techniques were developed for the addition and extraction of helium from water. A mass spectrometer and a pressure-volume apparatus were used for helium measurements at concentrations in water ranging from 1.5 to 5.5×10−4 milligrams per liter. In the field investigation, flow was traced through a confined aquifer for a distance of 188 feet. Both laboratory and field experiments showed that helium traveled at a slightly lower velocity than chloride. The advantages of helium as a ground-water tracer are its safety, low cost, relative ease of analysis, low concentrations required, and chemical inertness. The disadvantages include the relatively large errors in analysis, difficulties of maintaining a constant recharge rate, time required to develop equilibrium conditions in unconfmed aquifers, and possible loss to the atmosphere in unconfined aquifers.

THE FLASH PHOTOLYSIS OF DIACETYLENE

A brief description is given of a "microsecond" flash photolysis apparatus in which a 40 µf. condenser charged to 8000 v. is discharged through a photolysis flash tube in ~20 microseconds. Absorption spectra of transient species are photographed with a second flash tube which provides a source of continuum by discharging a 2 µf. condenser charged to 10,000 v., in 3–5 microseconds. A circuit for controlling the time interval between the two flashes is given.Experiments on the flash photolysis of diacetylene are discussed. With diacetylene at 0.5 mm. Hg pressure several well-known band systems were photographed in absorption 20 microseconds after the beginning of the photolysis flash, viz., the C2 Swan bands, the C2 Phillips bands, the C2 Deslandres–d'Azambuja bands, the 4050 Å bands of C3, and the CH band at 3143 Å. The rotational temperature of these bands was ~3000°–5000° K. The C2 Swan bands were also recorded in emission after a single photolysis flash. When a considerable excess (100:1) of helium was added to the diacetylene, all the above band systems disappeared with the exception of the C3 bands.In the absence of helium it is probable that the reaction is mainly thermal and that the high temperature is produced by a thermal explosion of the diacetylene triggered by the photolysis flash. The thermal reaction is suppressed by the addition of excess helium and the photochemical reaction becomes dominant. Under these conditions it is interesting to note that C3, but no C2, is produced. It appears therefore that C3 is a product of the photochemical decomposition of diacetylene. Possible mechanisms are discussed.

Studies in energy transfer III. The effect of added gases on the decomposition of cyclo butane

The effect of the addition of hydrogen, helium, neon, argon, nitrogen, methane, water, benzotrifluoride, toluene and mesitylene on the first-order rate constant for the decomposition of cyclo butane at low pressures has been measured. The results are compared with those obtained for the same gases under similar conditions for the isomerization of cyclo propane.

Pressure-induced absorption II: The calculation of pressure-induced absorption in hydrogen-helium mixtures

The theory of pressure-induced absorption developed in a previous paper is extended to include an explanation of the phenomenon in mixtures. The enhancement of H 2 and D 2 infra-red absorption due to the addition of Helium is calculated for 300°K, and the results are compared with the available experimental measurements. The theory explains the fact that the ratio of intensities S : Q is less for H 2He than for pure H 2.

Clinical Experiences in The Prevention of Cyclopropane-Oxygen Explosions by the Addition of Helium.*

Clinical Experiences in The Prevention of Cyclopropane-Oxygen Explosions by the Addition of Helium.*

Absorption of Light in Gases

CONTINUING an earlier experiment1, we have measured the absorption of light by caesium vapour in the presence of helium. We find that the addition of helium greatly reduces the absorption by caesium, about 3 cm. of helium being sufficient to reduce it to half the value obtained for caesium in vacuum. Frank2 and Mrozowski3 have shown that the continuous molecular absorption of mercury, zinc and cadmium vapours is proportional to P, where P is the vapour pressure and is a constant (for one wave-length). For different wave-lengths, lies between 1 and 2. Thus the absorption increases less rapidly than the molecular concentration. Their results may perhaps be explained if there is a reduction of absorption, due to collisions between atoms and molecules in the vapour, similar to the effect we have found in caesium and helium.

On Abnormal Rotation of Molecules

Hypothetical statements, explaining the abnormal rotation of molecules observed in band spectra, are tested by the investigation of the OH bands. It is known that the OH radicals are excited in the electric discharge through water vapor by simultaneous dissociation of ${\mathrm{H}}_{2}$O and excitation of OH. As expected, strongly abnormal rotation is observed in the emission spectrum. On the other hand, the absorption spectrum of OH in the electric discharge showing normal rotation, confirms the assumption just mentioned regarding the excitation process. By addition of helium the rotation observed in emission is reduced to its normal value; no appreciable persistence of rotation in collisions is evident. In order to judge whether in a given source the temperature can be derived from the rotational structure of the band spectrum, tentative rules are deduced from a review of the known processes by which abnormal rotation may be produced or destroyed. The intensity distribution of the vibrational structure of a band spectrum indicates the temperature of the gas only in special cases.